2521 L?.2 -//'' R35 190/1 BOUGHT WITH THE INCOME FROM THE SAGE EN'DOWMENT FUND THE GIFT OF 1891 ^M0M. ■ ^.|ITi|.i6 '!_ __ Cornell University Library QE 262.L22R35 1907 The geology of the Land's End district. 3 1924 004 ■sss'eas The original of this bool< is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004558635 MEMOmS OF THE GEOLOGICAL SURVEY. ENGLAND AND WALES. EXPLANATION OP SHEETS 351 and 358, THE GEOLOGY OF THE LAND'S END DISTRIOT. BY CLEMENT RETD, F.R.S,and J. S, FLETT, M.A, D.Sc. WITH CONTifelBUTION^ BT B. S. N. WILKINSON, B, E. L, DIXON, ^.So,, and W. POLLARD, M.\y, D.Sp. MINING APPENDIX BY D. A. MacALISTER, A.R.S;M. PITBUSHKD BV OBDSB 01 THE I.OBDS COMMISSIONESS OF ira MAJESTY'S TBEiaURf. LONDON: PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE BY WYMAN & SONS, LIMITED, FETTER LANE, B.C. And to be purchased, from E. STANFORD, 12, 13 and 14, Long Acbe, London ; JOHN MENZIES & Co., Rose Steket, Edinbuegh ; HODGES, FIGGIS & Co., Grafton Street, Dublin. From any Agent lot the sal6 of Ordnance Survey Maps ; pi- thu-ough any Bookseller from the Ordnance Survey Office, Southampton. ; Price 3s. 6d. LIST OF MAPS, SECTIONS, AND MEMOIRS OF THE GEOLOGICAL SURVEY OF ENGLAND AND WAL^S, AND MUSEUM OF PRACTICAL GEOLOGY. J. J. U. Tealk, M.A., D.Sc, F.K.S., Director of the Geological Slirvey and Museum, Jermyn Street, London, a.W The Maps and Memoirs are now issued hy the Ordnance Survey, l^liey can be obtained from Agents or direct front the Ordnance Surrey Office, Southampton. Museum Catalogues, GuldfiB, &e., are sold at the Museum, 28, Jermyo Street, London. A Complete List ol the Publications can be obtained from the Ordtiance Surrey Office, Southampton. Price id. INDEX HAF (25 miles to t%d iHeh). { Map of the British Islands. Price— Coloured) ii. ; Uncolonred, Is. QENEBAL UAF (one inch to 4 miles). BNGLAND AND VTALES.-^heet l(TltW); 2 (j^^orthamberland, cSie.|! Sttndejc of Colours) ; 4 (J. at Man); E (Lake , District); 6 (B. Yorkshire) ; 7 (North Wales); 8 (Central England)! SOSastem Counties); 10 (South Wales qid N 1. Deron) ; 11 (W. of England and S.E. Wales); 12 (London Basin and Weald); 13 (Cornvrall, &e.); 14 (South Coast Torquay to I. of Wight) ; 15 (S. Coast, Havant to Hastings). Sheet 1, ft. ; sheets 2 to 15, 2«. 6d. each. Printed in eOourt, NEW SERIES.— Drift, Sheet 8 (Fhvraborough and Grimsby), 2», ; Sheet iZ (Peterborough, Norwich), 2s. M. \ UAFS (one-inch). Old SeHes. Nos. 1 to 110 in whole sheets and quarter-sheets, liand-coloured, in two editions. Solid and Drift— excent 92 98 NW., SW. 97 SB., 9S KW., SW., S.B., 101 S.B., which are pubHShSd Solid only. Prices, whole sheets, S«. 6d. ; quartet-sheets, lir. ed. to 88. Sheet 7, Drift, ISs. 6d. MAPS (one-inoh). New S6ii6k. I to 7s. These New Series maps are identical with the Quarter Sheets ot the Old Series. Nos 91 to 110 all of wbi(Ji are published with Drift, excepting Sheets 29, 38, 48, 49, 61, 61, 62, 89, and 70. neJ: ts, i. Price. Solid. Drift. s. d. B. d. LONDON in tour Sheets (Colour printed) each ... — ISLE OF MAN Sheets 36, 45, 46, 56, and 57 8 6 110. MACCLESPIKLD (Colour printed) .. — 123. STOKE -UPON -TRENT (Colour printed) .. .. 16 141. LOUGHBOROUGH (Colour printed) — 166. ATHERSTONB , ^. SO 156. LEICESTER (Drift; Colour printed) 3 187. HUNTINGDON — 20S. BEDFORD — 230. AMMANFORD (Colour printed) ..16 2S1. MBRTHYR TYDFIL (Colour printed) 1 6 232. ABERGAVENNY (Colour printed) .. -X « 246. WORMS HEAD (Colour pi Inted) .. 16 247. SWANSEA (Colour printed) .. .. 16 248. PONTYPRIDD (Colour printed) .. 16 249. NEWPORT (MOH.X (Colour printed) 261-2. ERIDGENIi (Colour printed) .. 16 263. CARDIFF and WOBLB, SOMER- SET (Colour printed) ,. ,, 16 NEWBURY (Colour printed) ., ,. — BEADING (Colour printed) .. > .. — DEVIZES (Colour printed) ., ,. ' — ANDOVER (Colour printed) .. „ — BASINGSTOKE (Colour printed) .. — SALISBURY (Colour printed) .. — WINCHESTER (Colour printed) .. — NEW ALRESFORD(ColoHr printed) — WELLINGTON and CHARD (Colour printed) _ .. , -. RINGWOOD (Colour printed) ,. — 267. 284. 300. 811. 814. Pri(!. 315. 316. 317. 325. 330. 331. Solid. 8 'd SOUTHAMPTON (Colour printed) .. — ' HAVAlifT .. _ chioSBSter .. .. .'. .'" _ EXETBJB , .. _ and 3*- SIDMOUTH AND LYME REG|8 (Colour printed) .. .. _ DORCHESTER (Colour printed) .. — BOUEN&MOtTH, WIM BORNE, (Drift, Gdlour printed) . . . . so Parts of 1X^W FOREST and part of ISLE pir WIGHT (Drift, Colour pnntid) >. .. ..- .. .. 3 ^°^3'^5^i'.^S.''°d P"' 0' ISLE OF WIGHT (Drift, Colour printed) .. S OF WIGHT in one Sheet (Colour •SB., to teift.' s. d. ISLE printed) 332. BOGNOR, Ac. tColour printed) 3SS. WORTHING, feOTTINGDEAN 334. NEWHAVElf.SlASTBOURNE (Colour printed) . t» 339. NEWTON ABBO* .. .. ~ 341. WEST FLEET (Colour printed) 342. PORTLAND, WSYMOUTH, LUL- WORTH (Colour printed) . . 848. SWANAGE,CORFfi CASTLE.. 346. NEWQUAY (Colour jttihted) .. ~ 349. PLYMOUTH and IVYBBIDGB 860. TORQUAY 361 & 368. LAND'S END DISTRICT 862. FALMOUTH and TRURO (Ooloui printed) 365. KINGSBRIDGB .. 366. START POINT ] " 867 <& 860. ISLES OF SCILLY printed) MAPS (siz-incli). I 6 I 1 1 t 1 6 3 1 6 1 6 1 2 6 1 6 1 6 (Colour — 16 The Coalfields and other mineral districts of the N.of England (the N. Staffordahira nnii H w.i.>.\ nk'i« .^ leioestershire and Derbyshire, *ri In part published on a scale S six InohM to a mife MS CoZrLd V„«'^^^ .ix-inoh mans, not intended for publitiatlon.^re deposited for reference in the GtoSitoWtore^'omc? Jemln^V^^S."/ London, and copies can be supplied at the cost ol drawing and colouring the same. """'"y "mce, jermyn Street, • HOBIZOHTAL SECTIONS. 1 to 140, 146 to 143, price 6<. eaqh. VEBTICAL SECTIONS, lto86,price3>. 6(i.eaoh. CO I -si ?!5 o MEMOIRS OF THE GEOLOGICAL SURVEY. ENGLAND AND WALES. EXPLANATION OF SHEETS 351 and 358. THE GEOLOGY OF THE LA^ND'S END DISTRICT. BY CLEMENT RETD, F.R.S.,and J. S FLETT, M.A., D.Sc. WITH CONTRIBUTIONS BT B. S. N. WILKINSON, E. B. L. DIXON, B.Sc, and W. POLLARD, M.A. D.So. MINING APPENDIX BY D. A. MacALISTER, A.R.S.M. PUBLISHED BY OBDBR OF THE LORDS COMMI^^SIONERS OF HIS MAJESTY'S TREASURY, LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, By WYMAN & SONS, Limited, Fetter Lane, E.G. And to be purchased from E. STANFORD, 12, 13, and 14, Long Acke, London ; JOHN MENZIES & Co., Rose Street, Edinburgh ; HODGES, FIGGIS & Co., Grafton Street, Dublin; From any Agenb for the sale of Ordnance Survey Maps ; or through any Bookseller fro;n the Ordnance Sarvey Office, Southampton. 1907. Price 3s. 6d. PREFACE. The geological map accompanying this memoir combines the land-areas represented by Sheets 351 and 358 of the new series one-inch map. The original survey of the district was made by Sir H. T. De la Beche, and the results were pub- lished in 1839 on the old series one-inch map, Sheet 33. In the earlier issues of this Sheet the slaty rocks (killas) were simply coloured Grauwauke; but in the later issues from about 1846 onwards the rocks in question were coloured Devonian.* Additional lodes were inserted by Sir W. W. Smyth on a revised edition of Sheet 33, which appeared in 1866. On comparing the old map with the map to which this memoir refers, it will be seen that one of the most important differences is the reference of the slaty rocks to the Lower Palaeozoic period and their subdivision into three groups, to which the terms Portscatbo, Falmouth and Mylor have been applied. No characteristic fossils have been found in these rocks, so that some doubt as to their age may still remain ; for the reasons that have led to the classification which has been adopted, the reader is referred to the memoii-s on Sheets 352 (Falmouth) and 353 (Mevagissey), and to a paper by Mr. Hill on ' The Older and Newer Paleeozoics of West Cornwall ' {Oeol Mag., 1906, p. 206). The literature of the district is very extepsive, especially in the departments of mining and mineralogy. In mining we are lai'gely indebted to Hen wood, De la Beche, W. W. Smyth, R. Hunt, Le Neve Foster, Mr. J. H. Collins, J. Arthur Phillips, and Prof. H. Louis. In mineralogy the list of writers is too numerous to quote. For more than 200 years the district has attracted the attention of collectors and mineralogists, and in every good collection of British minerals a large number of rare and beautiful specimens that have been obtained from it will be found. To Samuel Allport and J. A. Phillips we are indebted for important papers on the microscopic structure of certain rocks, and to Mr. J. H. Collins for similar papers on Tinstones and Capels. But little work has been done on the stratigraphy of the * On De la Beche's ' Index to the Colours and Sigqs Employed in the Geological Survey of Great Britain for South- Western England and South Wales' — undated, but issued in 1846 or earlier— the tablet for Devonian rooks is thus given : — Devonian Rocks (A provisional colour, as tliere is reason to consider that the rocks included under this head in Cornwall and Devon are equivalents of Carboniferous Limestone, Old Red Sandstone,, and Upper Silurian Rocks). 9464. 4&3&2-Wt. 218S8. 6/07. Wy*S. district in recent years, and the maps previously issued are all based more or less on the early work of the lloyal Geological Society of Cornwall and on that of De la Beche. Of the early geological maps, the one published in 1822 by Dr. John Forbes, the map of St. Just Parish issued in the same year by Joseph Carne, and the geological map of Cornwall of 1832 by Dr. H. S. Boase, are deserving of special mention. In 1881 Mr. J. H. Collins published a map of Central and West Cornwall, in which the slaty rocks of this district are repre- sented as being of Lower Silurian age. The present map is based on a resurvey on the six-inch scale, which was commenced by Mr. Wilkinson in 1899. Mr. E. Dixon and Mr. Reid are also responsible for certain areas ; and. since 1 901 the work has been carried out under the direction of Mr. Reid as District Geologist. The areas surveyed by the different officers are noted on the list of six- inch maps given on page viii. All- these maps are available for reference in the Geological Survey Library, and eight of them, including the principal mining areas, will be published. The geological portion of the memoir is the joint production of Mr. Reid and Dr. Flett, the former being mainly responsible for the stratigraphical part, and the latter for the descriptions of the rocks. The Appendix on Mining is the work of Mr. D. A. MacA lister. In it will be found accounts of the distribution of the principal mining areas, of the nature of the lodes and ore-bodies of the mines, and of the yield of the different districts and of the individual mines so far as this can be ascertained. J. J. H. Teall, Dif'ector. Geological Survey Office, 28, Jermyn Street, London. May nth, 1907. CONTENTS. Preface by the Directok... ... ... ... iii Chapter I. — Introduction — Area, Physical Features Table of Strata, Geological Structure, Literature ... 1 Chapter II. — Killas, or Slaty Rocks — Mylor Slates... ... ... ... ... 7 Falmouth Series ... ... ... 18 Portscatho Sandstone ... ... ... ... 18 Contact- Altered Killas ... ... ... 20 Chapter III.— Greenstone and Metamorphism by Greenstone... ... ... ... ... 31 Chapter IV. — Granite and Metamorphism bs Granite 40 Chapter V. — Elvans ... ... ... ... 61 Chapter VI. — Tertiary ... ... ... ... 68 Chapter VII, — Drift — Raised Beach ... ... ... ... 75 Head and Stream Tin ... ... ... 77 Alluvium and Submerged Forest ... ... 81 Dunes ... ... ... ... ••• 82 Loss of Laud ... ... ... ... 83 Chapter VIII — Economics — Ore-Deposits ... ■ ... ... ... ■•• 85 Building Materials ... ... ... ... 89 Road Metal ... ... ... ... ... 90 Ornamental Stones ... ... ... .-• 91 Water Supply ... ... ... ••• 91 Appendix I. — Mining ... ... ... ... 93 Appendix II. — Bibliography ... ... ... 143 Index ... ... ... ... -•■ »" 147 VI ILLUSTRATIONS. PAGE Fig. 1. — Map of South-Western Cornwall ... ... 2 Fig. 2. — Diagrammatic Section across the St. Ertk Valley ... ... 69 Fig. 3.— Section at St, Erth (Kendall and Bell) ... 72 Fig. 4. — Section of the Cliff at the western end of Prah Sands 80 Fig. 5.— Sketch map showing the distribution of the minerals ... ... ... ... ... 101 Fig. 6. — New Balleswidden Mine. Cross section ... 104 Fig. 7. — Ding Dong Mine. Longitudinal section of Good Fortune Lode 104 Fig. 8. — Ding Dong Mine.. Longitudinal section of Bussa Lode 105 Fig. 9. — Ding Dong Mine. Longitudinal section of -New Lo'de 105 Fig. 10. — Ding Dong Mine. Longitudinal section of Malkin and Greenpease Lodes ... ... 105 Fig. 11. — Ding Dong Mine. Longitudinal section of Ding Dong Lode 105 Fig. 12 — Georgia Tin Mines. Cross section 106 Fig. 13. — Levant Mine. Longitudinal section, showing levels and workings 108 Fig. 14. — Levant Mine. "Workings on Main (or North) Lode 109 Fig. 15. — Levant Mine. Diagrammatic Sketch showing . Distribution of Tin and Copper Ore ... 110 Fig. 16.— Levant Mine. Cross section at Skip Shaft... 110 Fig. 17. — Levant Mine. Section at Old Submarine Shaft 110 Fig. 18. — Levant Mine. Section at New Submarine Shaft 110 Fig. 19. — Levant Mine. Section north-west of New Submarine Shaft 110 F'ig. 20. — Mellanear Mine. Cross section 113 Fig. 21. — Morvah Consols. Cross section 114 Fig. 22. — Wheal Owles. Longitudinal section of Wheal Boys Guide Lode 114 Fig. 23. — Wheal Owles, Cargodna ... 115 Fig. 24. — ^Tregurtha Downs. Cross section 117 Fig. 25. — East Tregembo Mine. Cross section 119 Fig. 26^— Wheal Friendship. Cross section 119 Vll Fig. 27. — Great Wheal Fortune. Cross section ... ... 186 Fig. 28. — Great Western Mine. Longitudinal section of Kendall's Lode 120 Fig. 29. — Gwin find Singer Mine. Cross section ... 120 Fig. 30. — Wheal Hearle. Cross section 120 Fig. 31. — Sithney and Carnineal United Mine. Cross section ... ... ... ... ... 120 Fig. 32.— South Wheal Speed. Cross section 121 Fig. 33. — Tindene Mine. Longitudinal section of Caunter Lode 121 Fig. 34. — Treloweth Mine. Cross section 121 Fig. 35. — Worvas Downs Mine. Longitudinal section of Main Lode, showing intersections with Caunter Lodes 121 Plate I. — View of the south side of the Land's End. Frontis- piece. Plate II. — Crag below Crowns Mine, Botallack Head. Plate III. — Granite Veins in Killas, Perth ineor. Plate IV. — Raised Beach in Penlee Quarry, near ( t3 g Mousehole. ( «> -3 Plate V. — Photomicrographs. \ ^ > Plate VI. — Photomicrographs. VUl LIST OF SIX-INCH MAPS INCLUDED IN ONE-INCH SHEET 351 & 358. 6lA. Gurnard's Head, by B. S. N. Wilkinson. 61 S.W. Zennor, Wicca Pool, Trevalgan, by C. Beid and B. S. N. Wilkinson. 61 S.E. (& N.B.) St. Ives, Carbis Bay , by O. Eeid and B. S. N. Wilkinson. 62 N.W. Godrevy, by E. E. L. D ixon. 62 N.B. Navax Point, Red River, by E. E. L. Dixon. 62 S.W. Hayle, Angarraok, by C. Raid. 62 S.E. Gwithian, Gwinetir Road, by E. E. L. Dixon. 67 N.W. Pendeen, by B. S. N. Wilkinson. 67 N.E. Morvah, Porthmeor, by B. S. N. Wilkinson and C. Eeid. *67 S.W. Botalloek, Boscaswell, by B. S. N. Wilkinson and C. Reid. 67 S.B. Chiin Downs, Ding Dong, by B. S. N. Wilkinson. 68 N.W. Zennor, Towednack, Oastle-an-Dinas, by B. S. N. Wilkinson and 0. Reid. 68 N.E. Towednack, Uny Lelant, Canon's Town, by 0. Reid and B. S. N. Wilkinson. 68 S.W. Gulval, Madron, by B. S. N. Wilkinson and C. Reid. 68 S.B. Ludgvan, by B. S. N. Wilkinson and O. Reid. *69 N.W. Uny Lelant, Hayle, St. Erth, by C. Reid and B. E. L. Dixon. *69 N.E. Gwinear, by E. E, L. Dixon. *69 S.W. St. Hilary, St. Etth, W. Godolphin, by B. S. N. Wilkinson, 0. Reid, and B. E. L. Dixon. *69 S.E. Godolphin Hill, Leedstown, by B. S. N. Wilkinson and C. Reid. *73 N.W. St. Just, by B. S. N. Wilkinson and 0. Reid. 73 N.E. Sancreed, by B. S. N. Wilkinson. 73 S.W. Sennen Cove, by B. S. N. Wilkinson and C. Reid. 73 S.E. St. Burian, by B. S. N. Wilkinson. 73a & 78a. Longships, by C. Eeid. 74 N.W. Madron, Penzance, by 0. Reid and B. S. N. Wilkinson. 74 N.E. Marazion, St. Michael's Mount, by B. S. N. Wilkinson and C. Eeid. 74 S.W. Paul, Newlyn, Mousehole, by B. S. N. Wilkinson and C. Reid. *75 N.W. Perran Uthnoe, Germoe, by B. S. N. Wilkiuson. *75 N.B. Germoe, Godolphin, Ashton, by B. S. N. Wilkinson. 75 S.E. Trewavas Head, by B. S. N. Wilkinson. 75 S.W. Cudden Point, Prah Sands, by B. S. N. Wilkinson. 78 N.W. Land's End, Sennen, St. Leven, by B. S. N. Wilkinson. 78 N.E. {& S.E.) St. Burian, St. Loy, by B. S. N. Wilkinson. 78 S.W. St. Leveu, by B. S. N. Wilkinson. 79 S.W. Tater-du, Lamorna, by B. S. N. Wilkinson. * In hand for publication. THE GEOLOGY OF THE LAND'S END DISTEIGT. CHAPTEE I. INTRODUCTION. The region to be described in the following pages consists mainly of the Land's End District of Cornwall, two one-inch maps (351 and 358) having been combined so as to include the whole of this natural division in one sheet. The deep depression, in former times alternately river valley and strait, which connects St. Ives Bay on the north with Mount's Bay on the south, forms the eastern limit of the true Land's End District ; but the map extends somewhat furtherj and includes a smaller area east of this old. strait. An inset map has been added, to show the positioli of the very singular and isolated Wplf Rock, which forms a sort of satellite to the Land's End, though geologically very unlike anything else in England. The' area, amounting in all to about 135 square miles, is a somewhat thinly-populated one. It includes the towns of Penzance and Hayle, as well as the rising watering-places of Marazion, Newlyn, St. Ives, and Carbis Bay. There are also a few mining villages, such as St. Just and Halse Town ; but the rest of the district contains only a small population, devoted mainly to agriculture. The mild, moist climate of this part of England, and especi- ally the mild winter, renders it very suitable for market gardening and the growth of flowers, and these industries have greatly increased of late years, especially along the south coast.' It is, however, a long way from large towns or good markets, and sometimes the prices obtained ir London have been barely sufficient to pay the carriage. As the population in the west increases and communications improve, this busi- ness and fishing are likely to replace mining, and become the staple industries of this district.' A certain amount of quarry- ing is done, especially for the excellent road metal,- which is now being worked by improved methods ; but the absence of convenient ports makes it difficult to use the valuable siipplies of good building stone, and the granite is only quarried on a small scale. In its physical features the region is a striking one, tor on three sides it is surrounded by the sea and a rocky coast Up to a height of about 420 feet the contours are smooth and fl(wing, forming a plateau which rises gently to a marked 9561 2 GEOLOGY OF LANDS END. blufe, formerly a sea-cliff. Above the level of 420 or 430 feet the land becomes bolder and more hilly, and at various points rises above 700 feet, the highest elevation being Trendnne Hill, 805 feet above the sea. Two of these higher areas, representing ancient islands, are found, the one including about two-thirds of the Land's End granite, though nowhere agreeing with it in its boundaries, the other only takmg m the high ground of Godolphin and Tregonnmg Hills. Fig. l.—Map of South- Western Cornuall, on the (cale of 6 miles to the inch . (Reproduced by permission of the Geological Society.) Above 400 Feet. 200-400Feet. Below ZOO Feet. ^m WoltRodk The coast is mainly rocky, the land ending in bold cliffs wherever the granite or the highly metamorphosed surround- ing rocks are cut into (see Plate I.). These cliffs, however, are not so high as we should expect, nowhere exceeding 300 feet, though the land reaches much greater elevations a short distance away, and the massive granite might easily form cliffs of much greater height. If the Land's End country is viewed from a distance — say from a steamer a few miles out at sea — the outline is very singular. There is a bold mass of high ground, usually end- INTRODUCTION. 3 ing in a noticeable bluff, tte foot of wbich is about 420 feet above mean tide. This blufi is strongly marked where it faces the Atlantic, less marked towards the east. At the foot of the bluff commences the plateau, which slopes gradually downward towards the present sea-cliff; but nowhere has the modern sea-cliff cut back far enough to obliterate the. old shelf. The sea is gradually regaining lost ground, and the cliffs, as they are cut back, become higher and higher; but the ancient shore-line is still far from being reached. The shelf just described slopes downward pretty regulal-ly to about 300 feet; but then it curves over and descends more rapidly to about 200 feet before it ends in the vertical cliff. This curve is a feature not confined to the Land's End, but apparently characteristic of West Cornwall. Even the nearly vertical cliff shows in every bay a notch or shelf, a few feet above the sea-level, on which lests a narrow strip of raised beach. This Pleistocene raised-beach platform in wide sheltered bays may expand to a considerable width. The western part of Cornwall is too narrow and isolated for the existence of streams of any importance, and most of the drainage of the granite area is probably subterranean. The Hayle River is mainly important in having a small harbour at its mouth; but there is a bad bar, and the harbour is kept open with difficulty. The Red River, which rises near Cam- borne and enters our area near Gwithian, is principally notice- able for its red muddy water, flowing from the Camborne mines, and containing sufficient tin to be worth collecting, even near the mouth. The geological formations represented on the map are as follows : — Alluvium and Submerged ] Forest - - - - f- Recent and Neolithic. Blown Sand - - - J Valley Gravel and Head - 1 pi • ± Raised Beach - - " J St. Erth Beds - - - Older Pliocene. Portscatho Series - - ] Falmouth Series - - >■ Lower Palaeozoic. Mylor Series - - - J Phonolite - Greenstone - - - Quartz-porphyry - - - !• Igneous. Granite (fine-grained newer^ Granite (coarsely porphyritic) The geological structure of this part of Cornwall may be described briefly as exhibiting a much-folded complex of sedi- mentary and igneous rocks, into which have been intruded thick and extensive sheets or laccolites of granite. The granite probably forms the floor at no great depth over the whole of the region described in this Memoir, for isolated areas of altered slate are found dotted about far from any granite exposure. After the intrusion of the granite: 9564 ^ ^ 4 GEOLOGY OF LAND S END. numerous dykes of quartz-porphyry were injected into the surrounding sedimentary strata ; later on similar fissures were filled with liot liquids or gases, which brought up and deposited the metallic ores now found in the lodes. The intrusion of the granite, judging by the evidence obtained in Devonshire, took place in late Carboniferous times; but between that date and the Older Pliocene the geological history of the district is a blank, except for some slight indications of Eocene deposits, which will be deferred to later on. In Older Pliocene times West Cornwall had already taken very much its present shape; but the land was submerged about 4,20 feet, so that only a group of islands was above water. This was perhaps the period of the formation of the high-level littoral platform already referred to ; though, judg- ing from other districts, it is not improbable that the feature is much older, and was only cleaned up and accentuated in Pliocene times. The Newer Pliocene period probably saw the formation of the curious slope which everywhere connects the older platform with the modern cliffl; but the exact date and mode of origin of this feature are still uncertain, for we have no deposits which can be referred to this period. Later on, the Pleistocene period saw a fairly rapid cutting back of the cliffs, and removal, by floating ice, of much of the fallen material which accumulated at their foot; but the whole of this, and the later periods, have only sufficed partly to obliterate the older features, which still show out with surpris- ing distinctness in the hard rocks of this part of Cornwall. The Land's End district at the present day changes very slowly, for neither rivers nor sea, without the aid of frost and ice, can act with much rapidity on such rocks. Where not polluted by mine-waters the streams run clear or peaty, and the sea is of an exceptional purity and transparency. The geological literature relating to this part of Cornwall is so extensive — for it has been a mining district from time immemorial — that it would be impossible in a few pages to mention a tithe of the writers. Perhaps the most convenient course will be here to take De la Beche's ' Report on the Geo- logy of Cornwall, Devon, and West Somerset' (1839) as a starting point, and indicate what has been done since in elucidating the geology of this difficult region. About the same time that De la Beche's Report appeared, Sedgwick, Murchison, and Lonsdale founded the Devonian system, and on the one-inch Geological Survey map, issued in 1846, the ' grauwaeke ' of De la Beche's original map is coloured and classed as Devonian. As regards the particular area now under consideration, it did not yield fossils, and seems merely to have been included in the new system, to which the fossiliferous rocks around Plymouth were referred, for lack of evidence to the contrary; in fact, De la Beche, in 1846, speaks of this area as not having been connected satisfactorily with the fossiliferotis rocks of New- INTRODUCTION. 5 quay and Plymoutli. This state of afEairs has lasted prac- tically up to the commencement of the new survey, though Mr. Collins has Inferred the slates of the Land's End district to the Lower Silurian system, and has .so coloured them in the map issued in Brenton Symons' ' Geology of Cornwall ' (1884). In 1898 Mr. J. B. Hill* divided the killas of West Corn- wall into four series, Veryan Beds, Portscatho Slates, Varie- gated Slates (afterwards Falmouth Slates), and Mylor Series, and these Lower PalsBOzoic divisions will be found fully described in his paper on some Geological Structures in West Corn wall, t and in the Memoir on the Geology of Falmouth. J Three of these divisions extend into the area here dealt with. Th© reasons for classing these deposits as Lower Palaeozoic were given in Mr. Hill's later paper. § The great advance in the science of petrology has increased our knowledge of the igneous rocks and ore deposits; and a copious literature relating to this area has sprung up since De la Beche wrote. We now know far more as to th© mode of formation and intrusion of granite, the genesis of mineral veins, and the origin of china-clay; while the microscopic study of metamorphic rocks was a thing un- known in his day. As regards the peculiar, highly-altered greenstones of West Cornwall, J. A. Phillips has minutely studied and analysed them,^ though they are still but imperfectly understood. The Tertiary and later deposits have a literature of their own, wTiich will be more conveniently dealt with in the chapters in which they are described. Pliocene strata were unknown in Cornwall till recently, and no suggestion had been made as to the clos© proximity of Eocene deposits, - though the unfossiliferous sand at St. Agnes Beacon was believed ' to be the remnant of same supracretaceous deposit.' The old ' diluvial theory ' so overshadows and tinges all work on the drift deposits of that date, that th© early accounts of these must be entirely re-written. De la Beche's Report, and the works of older writers, contain excellent descriptions of drift- sections now hidden ; but there is nearly always a bias towards cataclysmic action and a non-recognition of the long periods towards which these drifts point, consequently it is often diffi- cult to distinguish in published accounts between the very different deposits vaguely classed as ' drift ' or ' diluvium.' Since De la Beche wrote not very much has been added to our knowledge in this particular area. Mr. W. A. E. Ussher has brought together the published records, and has added a few details, in his privately-printed ' Post- Tertiary Geology of Cornwall ' (1879). In this pamphlet he corrected the old misapprehension, and placed the submerged forests as newer than the raised beaches. * ' Summary of Progress for 1898.' Mem. Geol. Siirvi'y, p. 97. t Trans. Roy. Geol. Soc. Corn., vol. xii., 1891, p. 1. t Mem,. Geol, Survey, liOG. § ' On the Relation between the Older and Newer Palreozoies of West Cornwall.' Geol. Mag., 1906, p. 206. T" Qxcart, Jo%wn. Geol, 8oc„ vol, xxxii., 1876, p. 155. CHAPTEE II. KILLAS OE SLATY EOCKS. Except for a few square miles in the north-eastern part of the map the whole of the Palaeozoic rocks here described seem to belong to a single period, and to one persistent type of remarkably fine-grained sediment. No fossils have yet been found, and as far as this district is concerned there is no clear evidence as to which division of these highly-contorted strata is the older. But from evidence obtained elsewhere it seems probable that the Mylor slates form the base. These are followed by a narrow belt of fine-grained silty and sandy slates, which in this area are of little importance, though in the adjoining map to the east they spread out over a wide extent of country. These Falmouth beds seem to form a passage or transition between the Mylor slates and the Portscatho sand- stone.* The whole of the rocks here described have been placed provisionally in the Ordovician system, for in the neighbour- hood of Veryan and Grorran (Map 353) the highest division seems to be continuous upward with strata containing fossils of Llandeilo age. Even there, however, they do not pass directly into strata of known date, for the Veryan calcareous series comes in between, and it is quite possible that these lower divisions in West Cornwall may be of Cambrian age, or perhaps even earlier. They do not appear to have any connection with the Devonian rocks of East Cornwall and Devon. The question will be asked : What thickness of rocks is represented in the area? But this question cannot at present be answered, even approximately. It would seem at first sight as if we were dealing with sediments amounting to many thousands of feet; but a close study shows that this view is probably a mistaken one. Everywhere we find evidence of sharp zig-zag folding, and of packing of the rocks by over- thrusting; so that at last the constant recurrence of certain types of sediment, and the apparent persistence of greenstone sills over wide areas, makes one think that, after all, we are dealing with strata only amounting to a few hundred feet, instead of having a thickness of many thousand. One point must always be borne in mind in a district of contorted rocks such as this— that the appai?ent dip is in reality only the dip of the limbs of the folds, and that as these folds were formed by lateral pressure they tend to set at right angles to the bedding as seen on a large scale. Therefore, as was pointed out some years ago by our colleague, Mr. Barrow, for the High- land rocks, the higher the angle of apparent dip the lower is the real dip, and vice versd. The Land's End region happens to * See J. B, Hill, in ? Geology of Falmouth.' Mem, Geol, Swvey, 1906 Chap 3. ' MYLOR SLATES. 7 be almost entirely one of liigL. dips; but it seems in reality to be a region of strata lying nearly flat (on a large scale), except for a small area near Hayle, where the bedding appears low and the strata are in all probability highly inclined. This high inclination on the northern margin of what appears to be a wide, shallow anticline may account for the small out- crop of the Falmouth series; these strata, being upturned, have here necessarily a narrow outcrop. The original thinness of the strata here suggested of course does not imply that a mine sunk in the syncline would reach the bottom of them in less than a thousand feet; they are ptobably so packed and folded together that the same beds might be penetrated again and again to a depth of several thousand feet. Kothing suggests that above any part of the granite floor in this particular area we should find rocks older than the Mylor series. Mtlor Slates. Most of the area covered by sedimentary rocks is occupied by singularly fine-grained clay-slates, or phyllites, of very uniform character. These slates, once silty muds, are usually well-laminated, soft, dull-black or dark-grey in cross fracture, but more or less glossy on the cleavage-faces, from the presence of abundant small fiakes of white mica. In some parts, especi- ally near the Falmouth beds, they become decidedly banded, and contain silty layers ; but essentially they are fine-grained slaty mud-stones, in which all fossils have been obliterated. Calcareous bands are very rare in this area. The dark-grey phyllites have a very perfect cleavage, but do not yield good roofing slate, because they are frequently cfumpled and inter- sected by small fissures and quartz veins. Quartz, white mica, and chlorite are their essential constituents ; iron ores, mtile, pyrites, and occasionally felspal" are also present. Biotite appears only where contact alteration takes place, and tour- maline is practically confined to the neighbourhood of the granite and the veins. The clastic quartz grains and worn scales of original mica, though still traceable where the rocks are least sheared, have for the most part disappeared in the process of reconstruction. The microscopic sections of the more fine-grained beds very often show the cleavage crossed by a ■ strain-slip ' cleavage at high angles. Towards the metamorphic aureole, which extends over nearly half the outcrop, there is a gradual change as the granite is approached. First, we observe a slight undefinable difflerence, the slate becoming merely a little harder, somewhat lighter in colour, more glossy on the cleavage planes; but no other change is recognisable. This obscurely characterised outer zone is too indefinite to be mapped as part of the aureole ; but the field-geologist can recognise it, and its existence must not be ignored, for the tin-lodes pass through the inner aureole into this outer zone, though very few of them go beyond it. As we approach still nearer to the granite masses we find 8 GEOLOGY OF LAND S END. next a zone of harder, paler-coloured slates, often finely- mottled or rather stippled, and showing either small crossed needles, or more commonly scattered rhomboidal spots of indefinite mineralogical character, but usually of different colour from the matrix. This zone comes on quite gradually, spotted slates at first alternating with unspotted, according as slight variations in original chemical composition rendered the slates more or less sensitive to the action of heat. Several of these partially spotted areas have been mapped by Mr. Dixon in the country between Leedstown and Godrevy, and, though the boundaries are somewhat indefinite, these isolated areas are important as suggesting that beneath the region probably lies an undulating floor of granite, the influence of which has not everywhere reached as far up as the present surface. Could we," in any part of the Land's End district, measiire the total thickness of the aureole at right angles to the granite surface, we might tell approximately how high above the granite we are at any point within the aureole. Thus far, unfortunately, we have been unable to obtain a satisfactory measurement. The height of the cliff is nowhere sufficient to show between top and bottom a perceptible difference in the amount of metamorphism ; the spoil heaps of the mines which commence in the outer zonesj or in the unmetamorphosec? slate, seem never to indicate a greater metamotphism at the bottom of the mine than is shown at the slate near the surface, though, unfortunately, none of these mines is now being worked, and we cannot be certain as to the exact depths from which the material came. Calculations from the known width of the aureole of meta- morphism, as laid down on the map, suggest that the aureole surrounding the Land's End mass may be from 2,500 to 4,000 feet in thickness, measured at right angles to the surface of the granite. Whatever may be the imderground slope, the thickness of the aureole cannot exceed the minimum width of its proved outcrop, which is about 4,000 feet. With an out- crop of 4,000 feet and a dip of 45° (which seems to be a common amount in this district) the thickness of the auteole would be 2,800 feet. This question of the extent of the aureole and the probable depth of the granite floor is a very important one economically; it will again be referred to in the chapters on granite and mineral ores. Roiieh calcula-. tions suggest the presence of an undulating granite floor at 4,000 or 5,000 feet down, with i-ising domes and bosses of granite, some of which reach the present surface, while others only rise sufficiently hisrh to cause the overlying aureole to appear at the surface as inliers amid the surrounding unaltered slates. After this digression we will return to the description of the aureole itself. The spotted slates become more and more tough, split less readily alonff the planes of cleavage, and tend to chanare to a brownish-grey, from the quantity of brown mica developed in them; but they still retain their even lamination up to within a short distance of tlie granite. MYLOR SLATES. 9 Tourmaline, in veins of scliorl rock, becomes more abundant. Close to the granite, and within the zone into which granite veins extend, the slates become much twisted, gnarled and knotted, are often full of tourmaline, and the gaps between the twisted laminte have been filled up with streaks and lenticles of quartz, of schorl rock, or of chlorite. In this innermost zone there is a local development of cordierite, garnet, and other contact minerals. The Mylor slates are so mixed up with sills of greenstone, so cut by elvan dykes, and so altered by the granite intrusions, that it will be most convenient to describe the coast section continuously. Here it will suffice to suggest the general geological structure of this region, and indicate where some of the best sections of these slates may be foimd. In rocks so violently contorted, and of unknown original thickness, it is not easy to say wha!t is the geological structure, until a considerable area has been minutely examined. Even now that the adjoining districts have been completely mapped, the isolation of the Land's End district by sea on three sides makes one hesitate to speak with absolute confidence as to certain points. The Mylor slates, on first examination, give the impression of evenly-bedded shales of great thickness, dipping at high angles. Gradually it becomes evident that they are true slates, and that though the cleavage commonly coincides with the ' colour-stripe ' it does not always do so. Bedding is not usually conspicuous in these fine-grained sedi- ments; but where it is traceable one finds occasionally the noses of sharp folds, though generally this part of the fold seems to have been sheared away. The finding of such a structure immediately reduces the probable true thickness of the slates to a small fraction of the thickness as measured across the strike. It shows, also, that the high apparent dip must coincide with a low real dip, when the strata are looked at on a large scale. The absence of beds of markedly different character, of lines of nodules, or of bands of fossils, makes the next step difiicult, for there are no minor horizons in the Mylor slates which can be identified with the smallest degree of certainty. We have also in this area no bottom to the series from which we can measure. Perhaps, however, a suggestion as to the probable magnitude of this division is given by the behaviour of the included greonstone sills. Thick massive sheets of greenstone surround the main granite intrusion in such a way as to siiggest that they represent the same sill, repeated to some extent by folding and overthrusting, but in the main sufficiently thick and massive to have resisted folding. The big sheets near Penzance are clearly parts of one mass, only separated bv denudation ; they have a moderate south-easterly dip, or dip away from the granite at an angle somewhat lower than that of the granite surface beneath. Masses of greenstone at St. Ives, Zennor, St. Just, and round by Tater-du may well be parts of the same thick sill. If these be really parts of the same thick sill intruded along the bedding, the strata in this 10 GEOLOGY OF LAND's END. part of Cornwall raust have been very slightly inclined before the intrusion of the granite, and the total thickness of the Mylor slates above and below the greenstone is probably only a few hundred feet.* The area between Carbis Bay and Ludgvan, where no thick sills occur, probably forms part of an anticline, continued eastward through Hayle and Gwithian; the interpre- tation of the south-eastern part of the area is more difficult. It will be seen that the greenstone shown on the map forms two diverging belts, much broken, sheared and disturbed. The northern belt, mapped by Mr. Dixon, passes Ludgvan, St. Erth, and Gwinear, running north-eastward, in the general direction of the strike. The southern belt, mapped by Mr. Wilkinson, runs east-south- eastward, through Marazion and Perranuthnoe to Cudden Point, where it seems to pass out to sea. Along this belt the greenstone forms a series of disconnected masses, all apparently striking nearly at I'ight angles to the general trend of the belt. Notwithstanding the coincidence of this strike with the direction in the northern belt, the greenstone seems truly to mark the southern limit of an anticline. Along the north- eastern ma:rgin the axis of the folding coincides with the general strike ; the sill, therefore, is fairly continuous, though the tock itself is badly sheared and overthrust. Along the southern margin, on the other hand, folding has taken place nearly at right angles to the strike ; the outcrop of the green- stone seems to consist therefore of a number of small broken synclines and anticlines. If this interpretation be correct, the thick sill was intruded before the folding, approximately parallel to the lower surface of the Portscatho sandstones. Both these rocks, used as geological horizons, give the same results; they suggest a gentle syncline, with axis running from Gwithian perhaps to the Land's End; and a gentle anticline, commencing near Ludgvan, its axis running north of St, Hilary, to Binner Downs, where it passes outside the area here described. This anticline is continued, however, in the adjoining map (352), in which it is traceable as far east as Truro. COAST SECTION. "We will now return to the description of the coast section, commencing at the Hayle River, where the Portscatho sand- stone is last seen. Unfortunately, the passage beds are hidden under Lelant Towans, and we can fix exactly neither the top of the Mylor slates nor the outer limit of the aureole of meta- morphism. It is evident, from the occurrence of a small tin- lode at the Ferry, that we are near the aureole; but here neither the Portscatho sandstone nor the accompanying bands * Smaller sills of slightly different character occur ; but these are of less importance and will be referred to later on. MYLOB SLATES. 11 of slate sliow any sign of spotting. When, tte cliff again becomes visible, just east of Hawk's Point, we at once meet with slightly-banded contorted slates, much toughened by the development of brown mica, and showing rhomboidal spots. These rocks vary from greenish-grey to dark-grey at the foot of the cliff ; but the upper part, in fact everything more than a few feet above the sea-level, is changed to buff or brownish tints. The strike is east-north-east, and the dip of the apparent bedding very high. A tongue of greenstone, 8 feet thick, is seen at the base of the cliff about 200 yards west of the point; but it disappears in a few yards, though another mass is found in the (iunwyn Quarry just above. The Hawkes Point Mine, which lies a few yards further west, is on a small lode of copper pyrites. At Carrack (Gladden the trend of the coast changes, so that the approach to the granite becomes more rapid. The cliff shows knotted homfels, with wavy cleavage, which is nearly vertical. This hornfels is hard, tough, and dark-coloured in the lower part of the cliff ; but in the upper part, and in the excellent sections seen in the railway cutting above, its colour is buff or even whitish. The coast approaches most nearly to the margin of the granite a short distance west of the Car bis Valley, and here the puckering and knotting of the slates becomes very pro- nounced. The cliff, however, has not receded quite as far as the junction of the granite and slate, and several mine adits which must cut this junction are now closed, and no plans of them are obtainable. The Providence lode is apparently a fault of small mag- nitude; but the published descriptions do not enable us to ascertain even the direction of the downthrow. This mine descended about 500 feet below the sea-level, and cut the junc- tion of the granite and slate at several points; but though Henwood describes the junction at 58, 68, and 76 fathoms below the sea, he does not mention its position in the levels. No plan of this part of the mine being available, we are unable to calculate the underground slope of the granite surface, though a note by Captain Penberthy to the effect that granite appears in the engine shaft at 50 fathoms below the adit would suggest a slope of about 55°. The western side of Carbis Bay calls for no special remark, except that the slates are full of tourmaline, and are a good deal stained by copper, small lodes of which have been worked. A narrow band of much-sheared greenstone is seen at the foot of the cliff opposite Trelyon, and Porthminster Point consists of greenstone and slate, inextricably mixed. St. Ives Head shows excellent sections of alternating green- stone and thin bands of slate, the slate often showing signs of contact alteration for a few inches from the greenstone. In such cases, though the cliff may consist of piled-up masses, resulting from the packing and overthrusting of a single green- stone sill, yet the lines of shear do not coincide exactly with the junction of the greenstone and slate. There is a tendency 12 GEOLOGY OF LANDS END. for the tough baked margin of the slate to become welded to the igneous rock, so that during subsequent movement the contact rock was preserved in its original relation to the green- stone, while the unaltered sediments were torn into thin laminae. The later metamorphism, caused by the granite, was superimposed on all these structures, and is of a different character; it does not change the slate in this fashion, into a pale-green porcellaneous rock. For the next two miles, as far as Seven Years Cove, the cliffs consist mainly of much-overthrust masses of greenstone, often containing streaks of killas. When the killas reappears in mass it has become much altered by the granite, and granite veins soon begin to appear in the cliff-face. The sediments have beon baked into a tough brownish or purplish hornfels, which, though showing perfect lamination, breaks almost as readily across the layers as with them. The intrusive veins will be described in a later chapter; it will suffice here to say that the sediments are of the usual fine-grained type, and that as we are apparently travelling along the strike we would not expect any change. The sections are excellent; but much of this part of the coast, which was mapped by Mr. Wilkinson, is difficult of access. The structure of Gurnard's Head is very like that of St. Ives Head, though on a larger scale. Masses of greenstone and altered slate alternate and pitch towards the sea at high angles. One of the best sections in Cornwall, of the contact of the granite with the slate and greenstone into which it is intruded, will be found in Porthmeor Cove, a small cove about two miles west of Zennor. It will be described in more detail in Chapter IV. The baked and knotted slates here seen are of the ordinary fine-grained character; but at this place, close to the granite, in a particular band small perfect crystals of garnet have been developed. Gatoets are not often found in the Cornish slates ; though masses of garnet rock are not un- commonly associated with the altered greenstone. Between Porthmeor and Portheras Coves granite forms the cliff for about two miles. At the last-named cove killas is again to be seen, with granite veins penetrating it, though the junction of the main masses is much obscured by head and raised beach. The cliffs from Pendeen to Cape Cornwall show the finest sections of metamorphosed rock in Cornwall, and they range from 200 to 300 feet in height. Only at certain points is it practicable to descend to the water's edge, for the lower part of the cliff becomes very precipitous, though the upper part tends to merge into a steep, craggy slope. Although these cliffs are cut by numerous narrow clefts or gullies, most of which seem at one time to have given access to the beach, yet such 'zawns,' as they are locally called, are now but seldom available as paths to the shore. Nearly all the zawns are formed by the removal of the vein material of tin or copper lodes, which is softer, or father crumbles away more readily MY LOB SLATES. 13 than tke surrounding ' country rock.' The lodes have in most cases been driven into down to the sea-level, so that the bottom of the zawn, instead of forming a slope, now com- monly ends inland with a vertical wall, \mclimbable except with the aid of ropes or ladders. Formerly, there were numerous miners' paths leading down to the sea-level — mere ledges along the face of the cliff, connected often with those above and below by ladders — but now that the mines have nearly all ceased working the paths are crumbling away, leaving numerous gaps, and the ladders that remain are so rotten that the greatest care is needed in using them. This stretch of cliff, extending for 3^ miles, runs along the strike, and similar rocks appear again and again. In a general way, the sections may be described as showing a mass of fine- grained sediment, into which has been intruded a thick green- stone sill, both dipping towards the north-west at about the same angle as the underground surface of the granite, which here slopes in the same direction. The slate and greenstone have been sheared up together at their junction in such a way as to form a beautifully laminated rock, consisting of alternate streaks of each (see Plate II.) ; further, this already laminated material has been baked by the granite into a solid, extremely tough hornfels, usually having a conchoidal or splintery frac- ture quite independent of the old planes of cleavage. Some parts of this mixed rock would make a beautiful ornamental stone, with streaks of brown and sage-green, and lenticles or eyes of pale-green or greenish-white. Specimens of it have been placed in the Museum of Practical Geology. Though the lamination is so conspicuous, and the slate is in places greatly puckered and folded, the ' knotted ' structure is less noticeable than in most parts of the interior of the aureole. The difference is probably due to the circumstance that here the intrusion of the granite happens to have taken place parallel to the divisional planes in the sediment, and has therefore not made them gape. Where the intrusion is across these planes, by end-on pressure it has caused them to open, so that quartz knots could be deposited in the gaps. This seems to be the reason why the contact rock near Carbis Bay, for instance, is so much more knotted than that of Cape Cornwall. Perhaps the best spots at which to study these altered rocks are the crags above Botallack Head, and for half a mile on either side ; also in the small bay known as Priest's Cove, immediately south of Cape Cornwall, and at Kenidjack, where a very beautiful cordierite hornfels occurs at the shoot- inw ranges. These altered rocks will again be referred to (see pp"! 27, 28). South of Cape Cornwall the trend of the coast changes to nearly south, and from that cape to Sennen Cove only granite is seen. At Sennen Cove the boundary curves eastward again, and the foreshore shows an excellent junction of fine-grained much-baked slate with the granite, one large granite vein being traceable for about 200 yards into the hornfels. A small west-north-west fault and quartz vein seems partly to account 14 GEOLOGY OF LAND's END. for the position of this killas; for the fault runs along the channel which separates Cowloe from the mainland, and it may help to explain why the island is entirely slate, without granite veins. These slates will be more fully described at end of this chapter (see pp. 23-26). The Land's End is granite, as are the outlying rocks known as the Kettle's Bottom, Shark's Pin, and most of the Longships group; but through the courtesy of the Corporation of Trinity House we have received from their engineer, Mr. Thomas Matthews, a piece of the outermost rock, on which the lighthouse itself is built. The bleck is a brownish-grey, fine-grained, highly- crystalline hornf els, very like that close to the granite at Cape Cornwall ; it proves, therefore, that the actual junction of the granite and slate must run through these islets. This helps to complete the curved outline of the granitic intrusion. There seems to be a tendency, south of the Land's End, for the nearly horizontal divisional planes in the granite to dip south-westward, and the average orientation of the large felspar crystals is in the same direction. This dip suggested that the outer limit of the granite was not far away from these cliffs. The discovery that the submerged rock known as the Runnel Stone is granite, not slate, shows, however, that the limit must be fully a mile ofE shore. This discovery was made in a curious way. A ship ran on the rock ; but was got ofi and towed into Falmouth Harbour, where she was docked. Still sticking in the hole in her bottom was a piece of the rock on which she had struck, and this has now been given by Mr. Howard Fox to the Survey collection. Near the Runnel Stone the trend of the coast again changes, and the boundary of the granite must turn also, for at Tater- du a mass of greenstone clings to the seaward slope of the granite, though here little kilias is found. Another three miles of granite cliff brings us to Mousehole, where the boundary of the granite is again seen, and turns inland. Here, on the foreshore, we find excellent exposures of much altered slates, penetrated by numerous granite veins and by veins of schorl rock. The resemblance of the succession to that near Cape Cornwall is so striking that it is difficult to resist the conclusion that we are examining the same beds on the two sides of an anticline. We have next the granite in each district, fine-grained slates, followed by a thick green- stone sill, and then by slate again. In both cases the strata dip away from the granite, at an angle not differing greatly from that of the granite surface. But though the granite has been intruded into this anticlinal arch nearly along the bedding planes, its dome is steeper than the arch, so that near Tremethick and north of Ludgvan the greenstone rests directly on the granite, as it does at Tater-du. The slate below the greenstone sill, as already remarked, is well exposed on the foreshore south of Mousehole Hatbour; that above the sill can be examined at Penlee Point, and on various parts of the foreshore on each side. Perhaps the best place, for examining the relations of the various rocks is at MYLOB SLATES. lo Penlee Point, for liere an outlier of tke upper slate clings to the dip slope, whilst the large Penlee stone quarry has laid open its junction with the greenstone for about a hundred yards. The adjoining Penolver Quarry, on the other hand, cuts entirely through the sill, and has now reached down to the slate below. These sections are most important as throwing light on the relations of the rocks, for the greenstone bakes the slate above into a porcellaneous rock, extending for several inches from the jujiction; thus proving, unless the whole succession is overturned, that the greenstone is an intruded sill, not an interbedded lava flow. The slate below the greenstone, seen in Penolver Quarry, was also carefully examined, in the hope that it might yield evidence of baking on the lower side of the sill also; but unfortunately this junction, as is so often the case near Penzance, is sheared away into hornblende schist, while the corresponding outcrop at Mousehole is obscured under the sand of the harbour. Penolver Quarry is being worked on a large scale, and at any time it may expose an undisturbed junction of the greenstone with the slate below. The metamorphism caused by the greenstone will again be referred to in the next chapter, in which the greenstone itself will also be described. The foreshore at Newlyn exhibits ledges of hard, knotted, flaggy hornfels, apparently below the greenstone, for the greenstone itself strikes out to sea at Carrick Symons's, which forms the southern horn of the harbour. The strike must follow closely the curve taken by the granite border, for though Newlyn itself is built on altered slate, greenstone re- appears at the sea-level at Tolcarne, rising steadily inland, just as it does at Penlee Point. The apparent break in the con- tinuity at Newlyn, shown on the map, may perhaps be due to a disturbance, which shifts all the outcrops, including the franite, considerably to the west. No clear evidence of this isturbance can, however, be obtained, for the border of the granite between Newlyn and Nancothan is obscured. An excellent section of the altered and spotted slate will be found in the quarry close to the Congregational Chapel, at Newlyn. In this quarry occur some of the fine-grained dark- green bands, described by J. A. Phillips as greenstone of peculiar type; these will again be referred to in the next chapter. The slate itself calls for no comment, except that close search was made in this quarry for fossils, but no trace could be found. The road above Newlyn, known as Paul Hill, is another locality whei-e Phillips obtained those green bands in the slate. The Coombe, which extends from Newlyn to the granite, lays open the structure of the country in an exceptionally clear way. East of St. Peter's Church the base of the green- stone descends almost to the sea-level ; though homfelsed slate can be seen in the stream-bed and in a quarry immediately opposite the church. As we enter the ravine the greenstone rises gradually at an angle of about 5°, so that the sheet forms 16 GEOLOGY OF LAND'S END. bold scarps on either side, beneath which the slate has been quarried. The dip of the planes in the slate seems here to be in the same direction as that of the base of the sill, i.e. east-south-east, but at. a higher angle. Search was made for fossils, especially in the large quarry a quarter of a mile west of the church; but none could be found, though the lamination certainly coincides with the bedding, shown by slight changes of colour and texture. Apparently we are again dealing with cleavage planes coinciding with shal'p folding. The base of the greenstone is about 50 feet above this quarry ; but the junction is obscure, for the greenstone tends to slip down the steep slope, and large fallen blocks of it occur even in the bed of the stream. It will be unnecessary to describe in detail the inland exposures of the slate, for they are very uniform in character, except for the varying amount of metamorphism observable as we approach or recede from the granite. It will be noticed, however, that superficial exposures within the aureole show rock differing greatly from the grey slate seen in deep quarries or on the foreshore, for they show buff or reddish spotted slates, which are so porous as readily to adhere to the tongue. There has been much oxidation of the slate, and probably much removal of the soluble silica ; for the slates are not calcareous. The foreshore near Penzance is greatly confused, with constant alternations of slate, greenstone, and a sort of horn- blende slate formed by the shearing of the other rocks. The exposures exhibit however at several points contact alteration caused by the greenstone. For instance, the Battery Rocks show slate above and below the greenstone, which here seems to have a thickness of about 40 feet. Above it the killas is much baked for an inch or two, the junction below the sill appearing to be sheared away. Similar porcellaneous slate at the junction is well seen on the foreshore under the rail- way bridge at Chyandour. In both these exposures it will be observed that the altered slate lies upon the greenstone. The large quarry opposite Coombe Cottage, up the Chyan- dour Valley, exhibits a greenstone sill, apparently over 50 feet thick, resting on dai-k-blue, black, or white slates, cleaved, sheared, and showing contact alteration for perhaps two, inches from the greenstone. Thus, unless this thick sill is overturned at one or other of the places, we have evidence here of contact alteration below it, and at Penlee Point of similar alteration above it. Penlee, however, is part of a big sheet, which it seems difficult to overturn; the Chyandour l-ock may be overturned ; but, if so, it is only additional evidence that the greenstone is an intruded sill, for then all the altered contact rock around Penzance is above the igneous mass. The flat coast between Chyandour and St. Michael's Mount is covered by sand, the only exposures of rock being certain ledges, only visible at low water. These show much-sheared rock — either slate or greenish schist — with occasional masses of more solid greenstone, and some elvan dykes. The whole foreshore is too obscure and the rocks too altered by weathering MYLOR SLATES. 17 for much to be said atout tlie Idllas ; but somewhere between the Cressars and Long Rock apparently must lie the outer limit oi the metamorphic aureole. Eound St. Michael's Mount another aureole occurs; but, as we should expect with this small boss of granite, the aureole is much narrower, being less than a quarter of a mile in width. Though the inland sections need not be described in detail, it may be convenient to point out where the best can be seen. In the little valley north-east of Gulval three quarries exhibit different stages in the metamorphism, the highest quarry being very near to the margin of the granite. The valley at Ludg- van shows also the increasing tiardness and metamorphism, beginning at Crowlas with a road cutting which must be close to the outer limit of the aureole, for the spotting there needs careful looking for. The slate outside the aureole can be examined south-east of Crowlas, in a quarry at Eospeath, and in the spoil heaps of various mines. The valley at Canon's Town also shows a number of small exposures, extending from the outer limit of the aureole to within a few yards of the granite, the total width of the aureole being here about three- quarters of a mile. Inland, over the eastern part of our area, evidence of the occurrence of the Mylor slates is everywhere to be found in the fine-grained grey slates seen in the jnine-tips, and in numerous small quarries; but the unmetamorphosed rock is too tender to be of much value for building. In this region Mr. Dixon discovered certain isolated patches of slightly metamorphosed slate, which seem to suggest hidden bosses of granite where none is visible at the surface. The areas, which are very . uncertain, are shown on the map. We will now return to the coast, at the point where we left it. East of Marazion the sections become less obscure, the rocky foreshore showing constant alternations of slate and greenstone, the slate often being much puckered, silicified, and veined with quartz. Where unaltered, the slate is dark- grey, with silvery cleavage planes, and a dull, earthy, nearly black cross fracture. Between Marazion and Hoe Point the slates are of this character; but at the western end of Prah Sands they come within the influence of another mass of granite, that of Grodolphin and Trewavas Head. The spoil heaps of the Sydney Cove, the Sydney Grodolphin, and the Leeds and St. Aubyn Mines yield grey slates with numerous minute crossed needles of andalusite — it is noticeable that round this granite mass we find needles of this character in the slate ; at the outer limit of the aureole inside this zone come the ordinary rhomboidal spots. A short dis- tance west of these mines the slates seem to be unaltered. Just west of Trewavas Head a mass of much indurated flaggy hornfels rests on the granite, the junction dipping steeply seaward. On the east side of the granite mass the metamor- phic slate is particularly well shown, being abundantly pene- trated by granite veins taking the form of sills. This cliff and foreshore exhibit the gradual dying out of the aureole as it is c 9664 18 GEOLOGY, OF LANd's END. traced away from the granite. The innermost zone of the aureole shows considerably less metamorpkism than that round the Land's End mass ; but the outer zone extends a considerr able distance to the east, probably owing to the low dip of' the granite surface in. that direction. ]pALM0UTH Series. These strata consist mainly of slates and silty beds, com- monly mor© or less banded, and.iii colour, at any rate near the surface, tending to shades of buff and reddish-brown, or alternations of purplish and pale-green. It , is exceedingly difficult to draw any satisfactory line between these rocks and the sandstones and finer muds found respectively aboye and below, the line engraved on the, map being a mere approxima- tion. The Falmouth series in the clifE at the eastern edge of the map is described by Mr. Dixon as consisting of green and dark-grey banded slates, with a little sandstone, similar strata occurring -inland near Trevorian. The green bands iave a soapy feel. Navax Point, shows cliiEs of banded clear-green, dark, and purple, clay slate, with siliceous laminae. The nearer of the. isolated rocjvs off the Point, consists chiefly of clear-green clay fllate, with ; dark-green metamorphic spots; but the spotting is local and apparently confined to particular bands. Beyoiid Navax Point it has been found, impossible to trace the Falmouth series as a separate division, though the dark striped slates under Upton Towans may represent this horizon. The proximity of the metamorphic aureole renders colour tests of little value, and all we can say is that a certain thickness of passage beds seems to occur even west of the Hayle Eiver, though these cannot be mapped separately. PORTSCATHO SANDSTONE. The newest slaty strata seen at the surface within the limits of this map seem, as already mentioned, to be those which appear in the cliffs east of St, Ives Bay. They consist of thin- bedded, light-grey pyritous sandstones, sometimes fine-grained, sometimes gritty, alternating with glossy dfirk-grey or striped slates, often having a soapy feel. Where the pyrites hag decomposed these strata become lighter in colour and tend to pass into shades of buff and red. It will be most convenient to begin the descl'iption of these rocks with the cliff at the northreastern limit of our district. This area, as far as Godrevy, was surveyed by Mr. Ernest Dixon, from whose notes- the following account of the county westward to Godrevy is taken. The cliffs from Hudder Down to Navax Point are difficult to climb, the shore being only accessible with any ease at two PORTSCATHO SANDSTONE. 19 points, Deadman's Cove and Fishing Cove. Close to the edge of the map, near the point where the high road almost touches the cliff, will be found a quarry in buff sandstones, with thin clay-slate partings, more persistently dark and unweathered. The dip here is only 8°, and probably represents the pitch of the folds, not the true dip. The rocks shown in Deadman's Cove consist of dark slates, which being soft have allowed the cove to be excavated. On each side the slate is faulted, against sandstone, and sandstone also appears in the upper part of the island in the cove, separated from the black slate below by a fault of low hade. This stack shows in its upper part sand- stones with thin partings of carbonaceous slate. As we follow the cliff westward another quarry is met with just above Hell's Mouth. The sandstone is here fine to moderately coarse, and shows a variable south-easterly dip. The next accessible section, at Pishing Cove, is very similar to that at Deadman's Cove, slates forming the cove and sand- stones the horns. The eastern part of this cove (called Castle Giver Cove on the six-inch map) is interesting as showing cliffs consisting chiefly of soft grey slaty sandstones, with metamorphic spots, alternating with thin bands of dark clay-slate. The rocks in this neighbourhood seem to be just at the limit of the aureole of metamorphism^ so that bands of a specially sensitive character may show the spotting, while in the associated rocks the metamorphism is not recognisable. Sandstones like those of Castle Giver Cove will also be found in the quarries at the edge of the cliff immediately to the north- west; similar sections occur inland in the neighbourhood of the Red Eiver, near Menedarva and Nancemellin. From Navax Point to Godrevy Point the cliffs consist of slates; but the outlying island of Godrevy, and also the dangerous rocks known as the Stones, are sandstone, as are the Bessack and Ceres E-ocks further south. Still following the coast westward, we again find sandstone on the foreshore beneath Upton Towans. The strike is north- easterly, and though the small area of foreshore not hidden by beach consists of sandstone, the whole of the low cliff con- sists of black or greenish striped slate, with perhaps a little soft grit at the junction. This soft grit is of the character commonly called ' felspathic,' but seems rather to consist of minute fragments of slate, out of which all colouring matter has been leached. Perhaps the cliff-section under Upton Towans exposes the actual junction of the Portscatho sand- stone and the Falmouth series, though here, as everywhere, there is much crushing and brecciation. Between the section just described and Black Cliff about a mile and a half of coast is hidden by sand dunes ; but fo some extent the boundary of the sandstone can be followed in the spoil heaps of the pits near the old arsenic works. The most northerly of these pits shows sandstone and black slate; the next five show only black banded slate, while a seventh — an open pit somewhat more to the west and out of the line- exhibits soft greenish slate and sandy micaceous grit, sug- 956* ^ * 20 GEOLOGY OF LAND'S END. gestive of passage beds. This would agree with, the line drawn near Phillack and Copperhouse, where sandstones occupy the north side of the river and slates the south. The best section of the Portscatho sandstone within our area is seen in Black Cliff, where thin-bedded sandstone and grit alternate^ with sandy slate and black and striped slate, all apparently dipping at a moderate angle towards the south-east. In al] probability this dip is altogether deceptive, and only represents the pitch of a series of extremely sharp zig-zag folds; but only here and there can any clear trace of folding be seen. The whole cliff, with its apparently even-bedded sandstones and shales, looks, at a short distance, more like a Coal-measure section than a cliff of much contorted rocks. When the beds are closely examined they are seen to be greatly sheared and cleaved, the cleavage commonly coinciding approximately with the bedding, though it often dips at a somewhat different angle. Even the hard sandstones every- where show signs of movement, flow and strain, so that it is not surprising that all attempt to find fossils in them has thus far resulted in failure. Quarries in the Portscatho sandstone will be found on the north side of Hayle Harbour, and the same beds reappear as alternations of shaly sandstone and coarse grit in the low cliff on the west side of the river, beneath the sand hills of Lelant, as well as in the adjoining railway cutting. In the Lelant sections the cleavage seems to run nearly east and west, the strike of the folding is about north-east, and the true strike on a large scale is apparently north-westerly. The most westerly section is seen in a small pit on the western margin of the golf links, which shows soft ' f elspathic ' or rather slaty grit, the white fragments being merely small pebbles of de- colourised slate mixed with some quartz grains. The rocks under Lelant Towans are close to the aureole of metamor- phism; but they show no sign of alteration, though at the Ferry a small tin lode is to be seen, and tin lodes seldom run any great distance outside the aureole. Special Peattjres of the Contact- Altered Killas. The West of Cornwall has long been known as a typical region for phenomena of contact alteration. Thirty years ago Allport investigated the changes in the killas with the aid of the microscope,* and Dr. Teall has also given a general account of the different types of rock found in the aureoles. The changes produced depend principally on the nature of the rock affected and its proximity to the granite; the elvans have a similar effect, though far less marked; the green- stones, however, produce an entirely different kind of contact alteration in the killas. By means of its fluoric and boric emanations the granite has modified the chemical composition * Allpovt, S., ' On the Metamorphic Rocks surrounding the Land's End Mass of Granite.' Quart. Jmmi. Beol. Soc, vol. xxxii., 1876. p. 407 J T H Teall, ' British Petrography,' 1888, p. 373, et. seq. • • «. '-'.. CONTACT-ALTERED KILLAS. 21 of some of the tocks adjoining it. It lias also to some extent melted up and absorbed the fragments of killas enclosed in it, as is proved by their rounded shapes. But the junctions between the granite and the slate are usually perfectly sharp and well defined, as was noted by AUport, and there is no evidence of an extensive interfusion of the igneous and the sedimentary materials. The spotted slates which occupy the major part of the meta- morphio aureole present a considerable variety of characters both in the hand specimens and in the microscopic slides. These variations are in pa^t original, but are also in some measure due to different modes and stages of decomposition, and to distinguish between the primary and the secondary features of these rocks is a matter of considerable difficulty. The spotting is most distinct in the rocks which come from the central part of the aureoles; as we pass outward into the unaltered killas it becomes more and more faint and ill- defined; in the inner zones again, which abut on the granite, the spots are often nearly or completely effaced by the exten- sive recrystallisation which the rocks have experienced. Weathering does not obliterate the spots, and may, in fact, make them more obvious, as the matrix becomes bleached, while they often retain their darker colour. In some cases the spots weather into hollows, and the surface of the rock has a honey- combed or vesicular appearance; They do not, in general, consist of different minerals from those which compose the bulk of the rock, and hence they have no sharp boundaries, but merge gradually into the surrounding groundmass. Hence they are more easily recognised with a hand lens than with more powerful magnifiers, and may be very indistinct in the microscopic sections, though quite clear in the hand speci- mens. Their general shape is rounded or ovoid, sometimes rhomboidal, their size up to a quarter of an inch in diameter, and they are not markedly flattened parallel to the foliation of the phyllite. In some localities they are elongated, giving the rock a resemblance to the German ' FrueUschiefer,' and in other cases they are irregular and streaky (' Garben- schiefer'). . . Although, in the vast majority of cases, the spotting indi- cates contact alteration, there are exceptions to this rule. Small, rounded, pale areas of quartz appear in many of the slides, both in rocks taken from within the aureoles and in those which lie outside them. They may be granulitised quartz pebbles or sections of small veins, or lenticular folia of quartz. Where there has been much contact alteration the quartz is mixed with or surrounded by reddish-brown biotite ; in other specimens chlorite, muscovite, and biotite are mingled with the quartz. In the phyllites near Gwithian and Hayle there are rhomboidal pale spots which are occasioned by small rhombohedra of brown ferriferous carbonates. These are well shown in the Gwithian hone-stone, which comes from a small quarry near Reskajeage ; they occur also in some of the coarser gritty tocks in this quarter. 22 GEOLOGY OF LAND's END. A distinct type of spotting occurs in the district near Bos«- worthy, Gwinear, mapped by Mr. Dixon. Small rounded spots stand out prominently on the broken surfaces of the fine, well-cleaYod, grey phyllites. They consist of quartz and chlorite, and in their present condition are probably secondary. Their original state is an "open question, as they may have formed from quartz-biotite aggregates, or after garnet or some other mineral. Mr. Dixon is of opinion that they indicate thermal alteration. We pass to consider those types of spotting which are pre- sumably of thermal origin, as they are only found within the aureoles which surround the granite. Their principal charac- ters have been already described. Although dark in the hand specimens they are sometimes paler coloured than the matrix in the sections, and may also show concentric zones or a dark periphery surrounding a paler centre. The essen- tial minerals of the spots are chlorite, muscovite, biotite, iron ores, tourmaline. The chlorite is very pale-green, or nearly colourless in ordinary light, and between crossed nicols is practically always dark. It is exceedingly finely subdivided, and often produces the impression that it is a secondary mineral. When it is the principal component of the spots they appear isotropic in polarised light. Anothe!r kind of chlorite with stronger double refraction less frequently occurs, usually in association with quartz. It forms radiate aggre- gates, giving grey interference colours, and is very similar to the chlorite of the tin veins. Muscovite, in very small colour- less scales, giving iridescent polarisation tints, is equally com- mon with the chlorite. Usually they occur together, forming felted aggregates, but in some rocks the muscovite is the main ingredient of the spots. These two minerals may have arisen from the alteration of cordierite, and the clusters of white mica may be secondary after andalusite. The biotite of the spots has the reddish-brown colour so common in the dark micas of contact-altered rocks; it weathers to chlorite mixed with much granular rutile. Except near the edge of the granite it is rarely fresh or well crystallised. Tourmaline, as a con- stituent of the spots, is confined to the tourmaline schists; iron Ores in small rounded grains, rutile in short simple or twinned prisms, and scaly graphite may also be present in the spots. It is very hard to make certain whether the chloi-ite and muscovite are primary or secondary, but there is good reason for holding that much of the chlorite, especially in the rocks from the inner parts of the aureoles, is formed at the expense of biotite, and the pale mica frequently seems to have replaced andalusite, cordierite, or felspar. This, however, cannot always be proved, and is, in fact, in many cases inherently improbable, especially in the rocks from the central and outer parts of the aureoles, where andalusite and cordierite cannot be shown to have developed. The fine micaceous shimmer- aggregates must then be really of primary nature. The spots are best developed in the most argillaceous and CONTACT- ALTERED KILLAS,. 23 finest roqks, and tte presence of any considerable amount of clastic quartz interferes with, the aggregation of chloritic and ^ijicaceous materials, which is necessary fey* the production of spotting, In the .plastic, heated rocK, full of interstitial moisture, and. probably also suffused with vapours from the granite, a separation of the ingredients took place very like the concretionary action which, goes on in soft argillaceous or calcareous sediments. The zoning of the spots, and the con- centration of certain minerals in them, while others were rejected, corresponds closely with the formation of concretions. This was accompanied by crystallisation, as in some of the more arenaceous rocks the spots are coarser grained than the surrounding matrix. Quartz is less common within the spots than around them, and often there is a dense peripheral zone of biotite, while the interior is free from it, showing that this mineral was rejected from the interior of the spots and accumu- lated outside them. Many of the rocks which contain a fair percentage of quartz, though, intensely altered by the granite, show no spotting whatever. In immediate proximity to the granite the spotted phyllites pass into hard, splintery, black or dark brown hornfelses, in whick the spotting is indistinct, or has vanished altogether, though the original foliation remains perfect. These rocks consist of biotite, quartz, fresh recrystallised felspar, rutile, iron ores, and sometimes a little tourmaline (biotite horn- felses). Excellent examples are to be obtained at Tater-du (see Plate VI., Pig. 6), Gape Cornwall, Porthmeor, and other localities at the edge of the granite. Andalusite, as reported by AUport, and confirmed by Dr. Teall, is frequent in these intensely indurated hornfelses. It occurs at Sennen Cove,. Cape Ooxnwali, Tater-du, St. Michael's Mount, Trewavas, Lesceave, and Lower Pent- reath. As a rul© its crystals are colourless, and not very well shaped. They show the usual prismatic cleavage but little or no dichroism in thin sections, and have not been observed with chiastolite structure. No definite rela- tionship between the formation of the andalusite and the spot- ting can be traced; in most of the andalusite hornfelses the spots have "already become obscure or have disappeared. In their growth the crystals reject the brown mica, and it does not appear within them in any quantity; hence the matrix surrounding the andalusites appears enriched in this mineral, and consequently dark in, colour (see Plate V., Fig._ 1). As the crystals are nearly white, a peculiar type of spotting with pale rhomboidal patches on a dark background arises m this way In othei- rocks the spots are still visible, but the anda- lusite seems to have formed entirely independent of them. In weathered rocks the andalusite may be replaced by aggregates of white mica, but frequently the andalusite is quite fresh., in rocks which in other respects are greatly ^cSierite is much more rare than andalusite in the meta- morphic aureoles, and the only localities from which tresh 24 GEOLOGY OF LAND's END. specimens of it have been obtained are Tater-dn, Botallack, and Kenidjaek, where the slates immediately in contact with the granite have been converted into cordierite-biotite hornfelses. At Tater-dn the mineral in question forms prisms one or two millimetres across, not idiomorphic, and composed of several twin individuals interpenetrating in an irregular way. It weathers to yellowish-green pinite. A few grains of green spinel, occasional needles of sillimanite, short prisms of rutile, grains of iron ores, and small crystals of corundum are present also in the slides. The biotite is reddish-brown, and, within the cordierite, forms small rounded or perfectly hexagonal tablets. A few flakes of muscovite and prisms of brown tourmaline are the other ingredients of the rock; neither andalusite nor garnet are present. Some of these cordierite hornfelses contain much acicular hornblende and will be described in a subsequent part of this chapter (see p. 28). Other specimens from the inner contact aureoles, where the conditions are less favourable for obtaining perfectly fresh material, contain irregular spots consisting of a mixture of white mica and chlorite, which can hardly be anything but pinite after cordierite. This mineral is far less resistant to weathering than andalusite, and in a district where surface decomposition is so advanced as in Cornwall, must have been replaced by secondary products in by far the greater number of its occurrences. Examination of a large number of slides of spotted Cornish hornfelses leads to the conclusion that cordierite was originally by no means uncommon in them. From Sennen Cove, Porthmeor, Cape Cornwall, and several other localities spotted hornfelses with areas of white mica, chlorite, and small grains of quartz, may be obtained which seem to fall into this category. The dark-blue or brownish enclosures of killas which abound in many of the Cornish granite quarries, more particularly in Lamorna, furnish by far the best material for the study of the extreme phases of thermal alteration of the sediments. Many of _ their features have been described by J. Arthur Phillips in a well-known paper.* They are typical hornfelses, fine-grained, splintery and very hard, and though their minerals are sometimes decomposed they are mostly in excel- lent preservation. They show no spotting, and the original banding or foliation is usually completely effaced by recrys- tallisation. The commonest mineral is a red-brown biotite, similar to that of the hornfelses on the margin of the granite It forms larger flakes and small idiomorphic plates enclosed in the other minerals. Quartz and iron ores also are always present, and a variable though usually small amount of felspar I^TOwn tourmaline is a frequent ingredient, sometimes in lal'ge prisms filled with grains of quartz and other minerals Zircon and apatite are both common. But the most character- „*J-A-- Phillips, 'On Corjcietioilary Patches and Fraemftnts of other Books Enclosed ;u Granite.' Quirt : Journ, Geol. Soc., vol. xxxvj., 1880, p. 1 CONTACT-ALTERED KILLAS. 25 istic ingredients are andalusite, cordierite, green spinel, silli- manite, and corundum. They do not all occur in every specimen; many are rich, in andalusite or cordierite, while spinel and sillimanit© are abundant in some slides but rare in others. The andalusite occurs in colourless prisms with good cleavage but imperfect faces. Both large and small crystals are pre- sent, tbe smaller being arranged in groupings of a sub-parallel nature. A faint rosy pleocbroism may often be noted when the polariser is rotated. The cordierite, which is often very abundant, is in small, rounded, perfectly transparent grains, with pleochroic halos and occasioqal penetration twinning. Larger crystals of irregular shape also occur. They enclose green spinel, biotite, sillimanite, and quartz. The spinel forms small dark-green octahedra, and rounded or quite irregular grains. In most of the slides it is very inconspicu- ous, but in others it is a common ingredient in larger crystals, which are readily detected. Sillimanite in slender prisms is fairly common, though it requires to be carefully searched for with high powers ; occasionally it forms divergent bundles of prisms a millimetre or more in length. Its enclosures are always few. The corundum is always colourless in thin sec- tion, and yields flat six-sided or rounded plates. Its presence is established with certainty by examination of the insoluble residue left after prolonged treatment of the rock powder with hydrofluoric acid. The small crystals thus isolated had a distinct blue colour, which varied in intensity. They easily scratched a smooth face of topaz. They were uniaxial and optically negative. Garnet has been reported in these enclo- sures by Phillips, but we have not yet found it in any of the slides; possibly the mineral he refers to is spinel. Only one occurrence of undoubted garnet in the hornfelses and spotted phyllites of this area is known to us, viz., at Porthmeor, in a thin band of biotite hornfels, but there are many chloritic pseudomorphs which might possibly represent this mineral. As will be clear from what has been said above, tourmaline appears in a great number of contact-altered specimens of killas, especially when they come from the immediate vicinity of the granite. It may occur in the andalusite, biotite, and cordierite hornfelses as an accessory mineral. In other cases, however, it is so abundant as to be highly characteristic, and replaces the usual brown biotite either completely or to a very large extent. These tourmaline hornfelses, tourmaline schists, or ' cornubianites '' have been described as regards their microscopic appearances by Allport and by Dr. Teall. They are usually local, and are found at the margin of the granite at Mousehole, Trewavas, Cape Cornwall, and other places. Generally they occur along lines of fissure, and quite the best specimens come from the tin veins or the altered country rock which bounds them. The tourmaline may be brown, yellow, or green, and sometimes has outgrowths and fringes of blue. When the alteration is complete the rock is converted into a banded schistose aggregate of tourmaline and quartz, exceed- 26 GEOLOGY OF LANd's END. ingly kard and resistant to weatkering; Evidently the pro- cess is one of pnemmatolytic replacement by solutions emanat- ing from the granite, and is an exact parallel to the formation of schorl rockj to be described in a subsequent chapter. All stages of it may be found, from rocks containing much biotite and a little tourmaline, to rocks in which the biotite has prac- tically completely disappeared. White mica may be common in these tourmaline schists, and they are often crossed by small veins of quartz containing tourmaline or felspar or sporadic crystals of tinstone, and other minerals which are mostly indeterminable. Evidently the tourmaline arises partly by replacement of biotite. (or chlorite) and felspar, partly by deposit from aqueous solution. The process, in other words, is metasomatic. Topaz, so frequent in the tourmalinized granite, has not been found in the altered killas, and the quartz-topaz rock which is abundant in some tin-bearing dis- tricts does not occur in this part of Cornwall. Another mode of alteration of the phyllites by heated solu- tions from the granite is the formation of muscovite-tourmaline schist. It also occurs especially at the granite margin and along the veins and fissures where the tin ores are found. The change is perfectly similar to that by which the granite is converted into greisen. Good examples are found at Cape Cornwall, Trewavas, Sennen Cove, and on the spoil heaps of old mines like the Providence Mine, near St. Ives. The shin- ing plates of muscovite are arranged parallel to the banding of the killas, and give the broken surface of the rock a silvery lustre, easily observed in the hand specimen. The other com- mon minerals are tourmaline, chlorite, usually a small amount of biotite, iron ores, zircon, and apatite. Quartz forms a con- siderable part of the rock both as distinct folia and as small grains enclosed in the white mica. Contact Alteration of the Killas by the Geeenstones. In many parts of the Land's End area the killas has been baked by the intrusive greenstones, and at the contact of the two rocks has been converted into a greyish-green, cherty- looking hornstone. The best instances of this type of altera- tion occur at Newlyn, Penlee, St. Ives Island, and Botallack, but many other localities show the same phenomena. The effects produced by the diabase are totally different from those produced by the granite ; tourmaline, brown mica, andalusite, and cordierite, which are the characteristic products of the granite metamorphism, are absent from these hornstones. They consist instead of alkali felspar and quartz, in a very fine- grained, cryptocrystalline mosaic, with many small stout rutiles, iron oxides, and occasional spots of chlorite, granules of epidote, and acicular prisms of green hornblende. The original banding of the killas is usually indicated in them, but never very distinctly. The rocks are typical fine-erained adinoles CONTACT-ALTERED KILLAS. 27 or spilositesi;. Small greenish spots appear in them frequently, and consist of chlorite, acicular green hornblende, and minute grains of rutile and iron oxides, but they are not very obvioufc. in the hand specimens. The prevailing grey-green colour and absence of spotting, in fact, serve to distinguish these rocks easily from those affected by the granite. Other points worth mentioning are that the greenstone alters the killas only to a distance of a few inches, while the aureoles of the granite extend many hundreds of yards from their mar- gins. Once, however, the sediments have experienced the modi- fying effects of the diabase they are little influenced at a subse- quent period by the granite. The adinoles are as well marked within the granite aureole at Penlee and Newlyn as in regions where no granite metamorphism can be traced. The rock taken from within a foot of the great sill of greenstone at Penlee is a typical adinole, though very fine-grained. At a distance of seven or eight feet from the contact, however, the hardened killas is brownish, and in microscopic section proves to be full of very minute brown biotites, with pale-coloured, irregular spots on a darker background. Here the granite has super- induced a new modification, bearing its own stamp, on a rock which has been only slightly, if at all, affected by the diabase. At the contact of the killas and the greenstone in the island of St; Ives there are crushed adinoles which are traversed by veins of green hornblende and other minerals. This killas is spotted with small rounded dark-teown spots of a mineral which we have not been able to determine. In the adinoles acicular green amphibole, as above described, is not uncommon in patches, veins, and irregular streaks. It may be partly primary, but its sporadic distribution and fre- quent occurrence in veins suggest that it is due to materials filtering in from the greenstone, or to a mechanical intermix- ture of the two rocks at the time when the whole series was being sheared. Actual breccias of killas and greenstone, form- ing crush conglonierates, are frequently to be observed on the cliff faces at Cape Cornwall, Botallack, and elsewhere. If these rocks are at a subsequent period baked by the granite it becomes very hard to tell what part of them is sedimentary and what part igneous. Veins and segregations of hornblende, accompanied by chlorite, epidote, garnet, and frequently axihite,' traverse the broken rocks either along the foliation or irregularly crossing it. It is not by any means impossible that hornblende should develop in the killas, as has taken place in some of the phyllites of Banffshire,* but from what we know of the chemical composition of the Cornish rocks it seems dis- tinctly improbable. Moreover, it is a suspicious circumstance that hornblende appears in the sediments only within very short distances from outcrops of greenstone. Allport has described and figuredt a variety of hornf els from liear Botallack containing acicular needles of nearly colourless * Mem. Oeol. Survey (Sootlimd), Sheet 85, Lower Strathspey, 1902, p. 53. t Loc. cit.,VL XXIII., Fig. 6. 28 GEOLOGY OF LAND'S END. hornblende (tremolite) in a banded matrix. He points out that the amphibole forms radiating groups crossing bands of black m^netite grains, which indicate the foliation or bedding of the rock, and that, consequently^ they belong to a later epoch of crystallisation, and have been formed under the operation of the heat emitted by the granite. In the rock collections of the Geological Survey there are specimens from this locality which answer very closely to Allport's descriptions. The rocks iire very completely recrystallised but have not lost their original banding. Acicular, pale-brown amphibole is their most striking constituent, and forms tufts, bundles, and stellate groups (see Plate V., Tig. 5). The slender prisms have rhomboidal cross-sections with the angles and cleavage of amphibole; their dichroism is hardly noticeable except in the thicker individuals. The homfels has a marked foliation, indicated not only by the parallel swarms of finely granular magnetite, but also by bands very rich in hornblende, alternat- ing with others in which it is less common. The rocks contain only a small amount of pale-yellow biotite. The colourless matrix in which these minerals lie is partly felspar in small granules, but some parts of the slides show large individuals of eordierite quite irregular in shape and crossed by undis- turbed lines of magnetite granules. Where fresh it shows penetration twinning and pleochroic halos ; when weathered it passes into golden-yellow pinite. This confirms Allport's opinion that the rock is a sediment, and proves also that the recrystallisation has been even more complete than he sus- pected. The original rock was probably one of the hornblende- bearing varieties of killas which ai'e found in close relationship to the greenstones. The best locality for eordierite hornfelses of this type is Kenidjack Castle. They also contain radiate acicular pale brown or colourless amphibole. Their eordierite is very fresh and shows the characteristic pleochroic halos. The rocks have a banded character in the microscopic sections, but in the hand specimens are nearly massive, very tough and may be free from spotting or may show large shining dark patches of eordierite. Many of the specimens have a vitreous lustre and a dark-bluish colour owing to the abundance and freshness of the eordierite. No finer eordierite rocks than these are known in Britain, and the presence of hornblende in them lends an additional interest, as this mineral is very excep- tional in rocks of this group. At the Congregational Church in Newlyn and on the shore besjde Newlyn Harbour, altered killas full of tufted pale needles of amphibole may also be found. They are less highly metamorphosed than those above described from Botallack and less perfectly foliated, but they belong evidently to the same group. The possibility that some of these hornblende-bearing phyl- lites and hornfelses may be volcanic tuffs ot sediments contain- ing fragments of basic rocks cannot be altogether excluded, and must be kept in mind. But where the field exposures are CONTACT-ALTEEED KILLAS. 29 good it is usually not' difficult to ascertain that the green- stones are really intrusive, and this is confirmed by the adinoles which accompany them. Moreover, the intermixture of greenstone and phyllite at the margins of the greater sills as the result of the shearing of two masses possessing very different rigidities can often be conclusively proved in the fiela. Phillips has described and analysed a suite of specimens of crystalline hornblendic slates collected from different localities in Western Cornwall. He proved that these rocks consisted essentially of dark-green hornblende. Some of his micro- scopic slides we have been able to examine in the museum of the Geological Society of London. They agree in nearly all particulars with his descriptions. The rock from Paul Hill is a felted aggregate of short prisms of hornblende with small grains of iron oxides. The hornblende is often grouped in small rounded clusters or ^ spots.' These features are all l-epeated in the rock from Chyandour. It is difficult to believe that materials of this nature can arise from the alteration, of slates: in fact, there is nothing in the slides which seems to us to favour the view that these are sediments of any kind. On the other hand, they resemble very closely the segregations and veins of hornblende which are so common in the green- stones when these have been intensely sheared and brecciated and at a subsequent period have suffered contact alteration by the adjacent granite. For most of our knowledge of the chemical composition of Cornish killas we are indebted to J. Arthur Phillips. The analyses of these rocks are given in his paper on the ' Rocks of the Mining Districts of Cornwall.'* These are sufficient to show that there is a considerable variation which is partly original, partly the result of silicification, decomposition, and other secondary changes, and may partly arise from the inclusion of analyses of rocks which do not strictly belong to the killas group. The silica percentages range from 67 to 40 (though there is one specimen with 32 per cent, of silica which Phillips does not definitely state to be a killas). This is quite in accordance with the results of microscopic investigations, which show that some of these rocks contain far more quartz than others, being more arenaceous, while in other cases, especially in the vicinity of the mineral veins, there has been extensive silicification. The most characteristic feature of these rocks is their high percentages of alumina— (20 per cent, to 24 per cent.) — ^while lime is present only in very small quantity, save in those exceptional varieties which contain hornblende. Without a fuller knowledge of the microscopic structures of the analysed specimens than is afforded by the descriptions given by Phillips, it is not possible to account for the variations m the chemical composition of the rocks he analysed. A specimen of brown hornfels enclosed in the granite of * Quart. Journ. Oeol, Soc, rol. xxxi., 1873, p. 319. 30 GEOLOGY OP land's END. Lamorna Quarry has been analysed , by Dr. Eollard, lin .the laboratory of the Geolog-ical Su1?vey, It. yields: — ■ SiOa .. 47-45 P.06 •26 TiOa .. 1-26 CI •04 AI2O3 .. 27-48 P. •37 PeOa .. 1-44 BaOs tr. PeO .. 8-60 (CoNi.)0 •02. MnO •15 CrijOs •02 CaO .. 2-23 YisOs ... ... ... •03 MgO .. 4-14 KaO .. 2-75 100-09 Na^O ... .. 1-62 Less for P and CI •17 LiaO •09 HgO (105°) ... •17 99-92 H2O (above 105°) . .. 1-97 This is sufficient to demonstrate that the rock is one of the more argillaceous types of killas, as its silica percentage is comparatively low, while the alumina is very high. ' The effects of the granite are traceable in the lithia, fluorine, and boric acid shown in the analysis, but' there is no reason to suspect that any increase has taken place in the soda and potash, and this corresponds with the general absence of felspathization in the Land's End hornfelses. Tourmaline and mica are the minerals which contain the elements infused by the granite; they indicate a very limited pneumatolytic action. The rock in question ife a brown, fine-grained, very fresh cordierite homfels. It is almost free from' banding and spott- ing, and consists essentially of cordierite and biotite. The cordierite is transparent, with well-marked yellow pleochtoic- halos, and forms a mosaic of small grkins and larger irregular crystals consisting of interpenetrating twins. The abundant biotite is reddish-brown, strongly pleochroic, with occasional very dark pleochroic halos. Its scales are mostly irregular, but the smallest may be hexagonal. The accessory ingredients are large irregular crystals of feebly pleochroic andalusite and yellow tourmaline, both full of enclosures of other minerals ; many small, imperfectly-shaped crystals of green spinel ; minute rounded crystals of corundum, colourless or of a weak blue tint; very small acicular sillimanites arranged in swarms in the cordierite; magnetite, zircon, apatite, pyrites. There is also a little muscovite, perhaps secondary, with slightly decomposed felspar (see Plate V., Fig. 2). 31 CHAPTER III. GREENSTONE. In the last chapter the stratigraphical position of the main mass of greenstoine was indicated ; it now remains to describe the greenstone itself,, the metamorphism it has caused, and the metamorphism it has undergone. We have also to describe certain minor exposures, apparently belonging to sills uncon- nected with the main mass. This account will probably be most intelligible if we com- mence with the description of the main mass in the area in which it is least broken up, and in which it remains most nearly in its original position. We cannot, unfortunately, start with an unsheared unmetamorphosed area, for such does not exist, the least sheared greenstone being found within the aureole surrounding the granite, whilst the greenstone outside that aureole is everywhere much broken up and sheared. We will commence, therefore, with the area immediately west of Penzance, where the structure is well laid open in deep quarries, rocky foreshore, and in ravines at right angles to the general strike. Before describing the various exposures it may b& well. to give in a few words our reasons for retaining the old terms for these igneous rocks instead of using a more modern nomen- clature. The rocks in question consist in this district of dark- green more or less sheared masses, much altered, and in many parts of the area subsequently metamorphosed by the intrusion of the granite. Under such circumstances it is not always easy to say what may have been the original character of these sills, and it is quite possible that more than one type may be included among them. Subsequent changes, however, have; been' so great as to bring these masses into one natural group of much-strained and altered basic igneous rocks, quite unlike any of the later intrusions which cut them and cut all the sheared structures. The microscopic structures of the ' greenstones ' of Western Cornwall -have been investigated by Allport,* Phillips,t and Dr. Teall.J The subject is by no means a simple one, as it is clear that the rocks originally included a number of different types, presenting some unusual features, and they have been decomposed, sheared, and, in many cases, contact altered by •the intrusive granite, till their original state and the means by which they have reached their present condition are not always easy to decipher. It might be possible to subdivide them * S. Allport, ' On the Metamorphic Kocks surrounding the Land's End Mass o£ Granite.' Quart. Journ. Qeol. Sob., vol. xxxii., 1876, p. 407. + J. Arthur Phillips, 'On the so-called Greenstones of 'V^estern Cornwall.' Ibid., p. 165. X J. J., Harris Teall. ' British Petrography,' 1888. 32 GEOLOGY OF LAND's END. into iiralite diabases, diabase porphyrites, diabase scbists, and diabase hornfelses, but for tbe group as a whole it is convenient to retain the old term, greenstone, the use of which has now become fixed in English petrographical nomenclature. Of their component minerals felspar is the chief. In many of the rocks it presents good idiomorphic outlines; in others its crystals are broken or dragged out and granulitised. Chemical analyses and optical investigations both show that it is often rich in soda and comparatively poor in lime, so that, taken as a whole, its composition is that of oligoclase and albite-oligoclase. Much of it shows intricate twinning on albite and Carlsbad laws, but in many slides there are also grains of untwinned felspar partly belonging to recrystallised water-clear albite, and partly to orthoclase. The original fels- spar may have been more basic than that which now prevails in the sheared greenstones, and its lime has probably been absorbed in the formation of epidote and leucoxene. Green secondary hornblende in fine fibres, which are clus- tered together to form patches and streaks between the felspars, is also constantly present in greater or less amount. It varies comparatively little in its optical properties, which are those ascribed to actinolite, and it has a well-marked pleochroism, in colours ranging from greenish-yellow to dark-green. It is never in well-crystallised compact individuals with distinct crystalline form (except where contact alteration has taken place), and usually its fibres are so thin that their cleavage is not well seen. As it forms a sort of groundmass or cement- ing substance in which the other minerals lie, the shape of its aggregates defies description. Often it is mixed with chlorite, sphene, biotite, epidote, and small grains of felspar, but in other cases the areas of hornblende are free from these im- purities. Iron oxides (ilmenite or titaniferous magnetite), more or less completely altered to sphene, are always visible in the slides, and a greater or less quantity of chlorite (giving bluish-grey interference colours) also occurs, mixed with the hornblende or partly replacing it. Yellow grains of epidote are not infrequent. Small scales of brownish biotite are common in some rocks, but mostly indicate a certain amount of contact alteration. The coarser rocks show numerous large crystals of apatite with perfect hexagonal cross sections. The presence of pyrites is almost universal. Quartz, calcite, leucoxene, and limonite are among the second- ary products. White mica not uncommonly arises by weather- ing of the felspar. Although augite is well known to occur in some of these greenstones, it is probably never an original mineral, but a product of the thermal action of the adjacent granite. Biotite, brown hornblende, axinite, tourmaline, and garnet are fre- quently found also under the same circumstances. The more massive greenstones, whether they were originally intrusive sheets or interbedded lavas, have in many cases suffered little from the deforming inovements by which the GREENSTONE. 33 killaa has been so greatly disturbed, and even where parts of a greenstone are greatly sheared there are usually other parts which have escaped crushing and have served as phacoids, around which the adjacent rock was compelled to flow. Hence it is often possible to make out the original structure of the rock, and to refer it to certain of the established categories. There is nothing in the microscopic characters of the green- stones of this area which makes it certain, or even probable, that any of them represents a contemporaneous, interbedded lava. Ophitic structure, though by no means uncommon, is far less general than might have been anticipated in large intru- sive sheets. The felspars retain their idiomorphism, and yield broad, squarish, or rectangular sections. Their twinning is usually complex, and when they are fresh it is sometimes possible to establish that they belong to albite-oligoclase and oligoclase, but more basic varieites also may occur. Augite is represented entirely by uralite and chlorite enveloping the felspars. Fine granular yellow epidote often mixes with the chlorite. Large networks of ilmenite and prisms of apatite are frequent in the rocks of this group. Generally, there are indications of shearing, and the felspars become fractured and dislocated. The hornblende is forced into their crevices. The ilmenite networks are dragged out and partly converted into leucoxene, and the large apatites are broken across into seg- ments, which are displaced relatively to one another. Exam- ples of this group are furnished by some of the sheets at Mara- zion (see Plate V., Fig. 4), parts of the Newlyn mass, and by several sills near Treglistian (Hayle). Another group of these sheared diabases is finel- grained, and shows small lath-shaped felspars, often with a parallel arrangement, which may be partly the result of crushing, but is probably also an original fluxion structure. Between the felspars there is chlorite and finely fibrous actinolite, grains of iron ore, and occasionally epidote. If these rocks are much crushed, veins of hornblende very commonly traverse them, and the felspar may be altered into fine scaly mica, with strong double refraction, by crushing or by decomposition. Granular leucoxene and pyrites are also frequently present. Some of them contain rounded or irregular patches of chlorite or actinolite, which much resemble flattened compressed steam cavities, but may, perhaps, be pseudomorphs after some ferro- magnesian mineral. These fine-grained diabases might quite well, from their structures, have been contemporaneous lavas, but in some cases they are certainly the chilled edges of intru- sive masses. Good examples are to be obtained at Chvandour (see Plate V., Fig. 6), Chenhalls, Lescudjack, Carrick Du, and Carnabargas. Closely allied to the fine-grained varieties mentioned above are certain rocks which exhibit the remains of variolitic struc- ture. Their felspars are elongated laths grouped in radiate bundles, and embedded in a matrix composed of secondary chlorite, actinolite, and leucoxene. Eocks of this type are D 9564 34 GEOLOGY OF LAND's END. known from Roseworthy (Grwinear), between Lay Point and St. Ives, and from the upper quarry at Carrick Du. 'Sh.ej are presumably the margins of intrusive masses. ,- ; In other cases traces of porphyritic structure remain; idio- morphic felspars may be seen lying in a matrix of smaller felspars and decomposition products " after ferro-magnesian minerals. The greenstone at the north entrance to Penzance Harbour is of this type (see Plate V., Fig. 3), and parts of the Newlyn intrusive sheet also show this structure. These original characters are more or less effaced, according to the amount of shearing to which the rock has been sub- jected. In the majority of microscopic sections of these green- stones the igneous structures are only imperfectly preserved. The felspars are broken and dislocated, filled with chlorite and actinolite, and are ultimately converted into granulitic mosaics of small untwinned grains. The ilmenite is replaced by granu- lar sphene ; the chlorite and actinolite, with more or less epidote, form elongated streaks parallel to the foliation of the rock. The apatites are broken up into small grains. White mica develops from the felspar. The result is a diabase schist, which sometimes has a very good foliation. Eecrys- tallisation has not gone on in these rocks to any great extent. The hornblende remains fibrous, and does not build up compact plates, and though a little new water-clear felspar develops it is not conspicuous. Typical hornblende schists like those of the Southern Highlands of Scotland are not known from the Land's End area. Evidently the crushing did not take place under any very great load of superincumbent strata. In some districts the finer-grained diabases are not only sheared but are much brecciated, and consist of phacoids of greenstone surrounded by a plexus of veins. The best known examples of this are near the granite margin, especially on the west side near Levant, where thete has been a considerable amount of contact alteration. Parts of the cliff are faced with broken altered greenstone, forming a ci"ush breccia or crush conglomerate, intersected with veins of hornblende, epidote, augite, garnet, etc., which produce a beautiful rock which, except for its hardness and brittleness, would be suit- able for an ornamental stone. But this phenomenon is very general, especially in the smaller and finer-grained sills. Segregation seems to have accompanied the crushing, as there are often large veins of hornblende, mixed with epidote and chlorite, and, in the districts where there has been contact alteration, with pyroxene, axinite, garnet, and sometimes tourmaline. Veins of matted hornblende fibres, an inch or mote in thickness, produced by shearing, segregation, and sometimes also contact action, are common in the greenstones near Pen- zance, and it seems likely that the analyses given by J. A. Phillips (loc. cit., p. 165) of some very basic hornblende schists from this locality refer really to products of this nature. A chemical analysis of the Newlyn -diabase, which has been so largely quarried for road-mending purposes, has been pre- L U. SiOa ... 59-84 . . 50-57 TiOa m , A1^8 ... ... 15-71 . .' 19-65 FeaOs ... ... 1-68 . 1-46 FeO ... 7-03 . . 7-24 MnO ... •12 .. tr. CaO ... 3-71 . . 7-47 MgO ... ... 1-37 .. . 7'93 J. II. 2-76 ... 1-08 6-52 • •• 3-46 -10 FeSj tr. -20 ... -12 •14] •31 j •74 GREENSTONE. ^ 35 pared hy Dr. W. Pollard and is given below, along witli another analysis of a similar rock from the same loealitv bv J. A. Phillips:- J- J' L U. NaaO S. PA HjO (at 105°) H2O (above 105°) 100-13 ... 99-72 I. 0wavas Quarry, Newlyn, Cornwall. Anal., Dr. W. Pollard. II. Quarry in the village of Newlyn. Anal., J. A, Phillips {Quart. Journ^ Geol. Soc, vol. xxxii., 1876, p. 167). A comparison of the two analyses shows that the rocks are not identical, though closely allied, and this is easily ex- plained by the considerable variation which can be proved tp exist in the character of this intrusive sheet by an inspection of the exposures in the quarry and on the beach below. There are at least two distinct varieties, one paler in colour and being rich in felspar, the other dark-green and containing a larger proportion of hornblende. Phillips's specimen had very nearly the composition of an average diabase, but has rather more alkalies, especially soda, than is usual in the rocks of this group. The rock analysed by Dr. Pollard, how- ever, has far too much silica and alkalies and too little lime and magnesia to pass as an ordinary diabase. These bring it much nearer the group of augite andesites, and the spilites, with some analyses of which it is closely comparable. Its high percentage of alkalies (9.28) is especially noteworthy. The soda (6.52) is nearly twice as abundant as the lime (3.71), and this shows that if we allow for a little lime in the sphene and the hornblende the felspar must be of the average composition of acid oligoclase. This is confirmed by a microscopic ex- amination of the rock, which shows that it is full of felspar, with angles of symmetrical extinction too high for oligoclase, and with a refractive index below that of Canada balsam. Part of this is water-clear recrystallised albite and ortho- clase, but most is albite oligoclase. Some normal oligoclase is probably also present. The hornblende of this rock, though fibrous, is dark-green, with pronounced pleochroism (clear yellow to dark-green). It fills the s;paces between the larger partly idiomorphic felspars. There is also a little granular felspar, which serves as a sort of groundmass. Biotite, mag- netite, and sphene are present in small quantity, and there are a few crystals of apatite and pyrites. This rock is much fresher than the majority of the green- stones in this sheet, and the character of the hornblende, along with the presence of biotite in place of the usual chlorite, show that it has undergone contact alteration from the adja- cent granite. It is, in fact, one of the less advanced stages in the production of diabase-hornfels, a process which we shall now briefly consider. »664 . ° 36 , GEOLOGY OF LANd's END. Contact Alteration op the Geeenstones by the Granite. Tliis phenomenon is very general around the Land's End granite mass, and is of importance, as it has indurated the greenstones, and by recrystallising their felspar and their hornblende to some extent, has.giTcn them that hardness and toughness which make them so valuable as road-mending stones. Fresh minerals have been substituted for the decom- posed minerals of the normal greenstones, and the wearing properties of the rocks have been enhanced. The less advanced stages of hornfelsing, such as are found within 100 yards or so of the edge of the granite, have been instanced in the Pen- lee rock of Gwavas Quarry. We note particularly the bright fresh felspar, the strongly pleochroic green hornblende, and the presence of a small amount of dark-brown biotite. Many of the greenstones around Penzance, Newlyn, and St. Ives show the same kind of alteration. The greyish-green coarse diabase which is quarried at Gunwyn, Lelant, is an excellent example of the rocks of this class, in many respects closely comparable to that of Gwavas. It has suffered, though only to a slight extent, from, shearing, and the contact action of the adjacent granite has also affected it, though not very greatly. In the hand specimen the rock is rather pale coloured, with large fresh felspars which have bright cleavage surfaces; more than one variety is obtained in the quarry, some being finer-grained than others. In place of the green hornblende which prevails in the Gwavas rock, we have here abundance of chlorite mixed with brown biotite in small scales clustered together. The fresh biotite indicates contact alteration; the irregular aggregates of these two minerals replace original pyroxene, which has entirely dis' appeared. By their distribution they render it probable that the rock had, in parts at least, an ophitic texture. The other ingredients are ilmenite or titaniferous magnetite, pyrite. apatite, quartz and felspar. The iron oxides form networks and patches of ill-defined shape surrounded by biotite. Apatite is very abundant in long hexagonal needles, often broken or bent. Quartz is rather scanty, and fills some of the interspaces between the felspars ; it contains cavities with little cubes and mobile bubbles surrounded by a liquid. This mineral is not certainly an original ingredient of the rock. The abundant felspars have often squarish or rectangular out- lines, but in places are crushed to a mosaic of irregular grains. They are mostly in good preservation, and being chiefly to a variety of plagioclase, very rich in soda. This is proved by their refractive indices (lower than those of quartz), their moderately high extinction angles in sections perpendicular to the albite twinning, and by the extinction angles in sections perpendicular to the acute and obtuse bisectrices (Fouque's method). Varieties containing more lime than albite- oligoclase were not observed. Areas of untwinned or simply twinned felspar with veinlets and patches of albite are also present (microperthite) ; they are less frequently eumorphic (JREENSTONE. it than the plagioclase. The microscopic characters of this rock indicate that, like that analysed from Ghvavas Quarry, it must he rich in alkalies and poor in lime, and differs widely in thesse respects from normal types of diabase. But, as the greenstones ar© difficult rocks to recrystallise completely, the final stages of alteration are only to be found within a short distance of the granite. At St. Just, Porth- meor, St. Ives, Tater-du, and other localities, where the green- stone is taken from immediate contact with the granite, it is often greatly modified, having been converted into a splintery, brown or dark-green lustrous hornfels. These rocks often show small needles of black hornblende and shimmering, brownish scales of biotite in the hand specimen, and may be crossed by veins of acicular amphibole, augite, epidote, etc. Many of them are curiously banded with paler, more fels- pathic streaks, alternating with darker coloured patches. This is principally seen near the edge of the greenstones, where differential movements may have taken place between them and the killas, with production of a certain amount of breccia- tion. But it is partly due also to a tendency to the agglomera- tion of newly-formed biotite, epidote, augite, and hornblende, into knots or clusters similar to those which are so well known in contact-altered sediments. At Chyandour, Chenhalls, etc., these phenomena are well marked, and haVe been alluded to by AUport,* but it is possible that the dark spots may in some cases be original vesicles in the fine-grained edges of intrusive sills (see Plate V., Fig. 6). Although these diabase hornfelses present a very great variety of structures, and differ considerably in the relative abundance of tEeir components, they consist of only a few minerals. These, however, differ in many respects from the constituents of the unaltered diabases. Hornblende is ex- ceedingly common, and in the extreme stages of contact altera- tion it is always of a rather pale-brown or brownish-green colour. It may. form fairly large crystals, with lozenge- shaped cross sections bounded by the. prism faces, and several times as long as broad, but it occurs also in slender, straight needles, which are so thin as to be only faint yellow and feebly dichroic. The larger prisms are scattered irregularly through the rock; the finer needles group themselves in radiate star-like bundles. Even these, as noted by AUport, have lozenge-shaped transverse sections. In a few rocks this brown hornblende is partly in granular equidimensional crystals. In others it is entirely acicular, and in some these needles are so very fine, scattered through the felspar or form-" ing small tufts, that it is only by analogy that they are referred to hornblende. Somewhat less abundant, though plentiful in many of the rocks, is a colourless or very pale-green augite, in small ill-shaped crystals, which occupy certain bands or folia of the rocks almost to the complete exclusion of any other • S., Allpoi-t, 'On the Metamorphic Rooks surrounding the Land's End Mass of Granite ' Quart. Jowrn. Geol. Soo., vol. xxxii., 1876, p. 419. 38 GEOLOGY OF I/AND's END. constituents. They are of varying size, many being so small that they are with difficulty recognised as augite. Dark-green hornblende often partly surrounds the augite and is apparently of secondary formation. In certain less altered rocks green augite also is abundant in crystals up to .5 millimetre in diameter, associated with crystals of compact green hornblende (Chyandour, Chenhalls, etc.j. Even in such circumstances it is probably a contact-alteration product, as it occurs only whel'e there are signs of the thermal action of the adjacent granite. In a specimen taken from the margin of the granite at Mouse- hole the augite has a reddish-brown colour and is surrounded by biotite and green hornblende. Brown biotite in small irregular scales, strongly pleochi-oic (yellow to dark reddish-brown), though absent from some of these rocks, is a common ingredient of most of them. Un- twinned and twinned felspar, either in small grains or in large plates, but never idiomorphic, forms a sort of groundmass in which the other minerals lie. Where determinable it belongs to oligoclase and has a refractive index almost exactly equal to that of hard balsam. Iron ores, minute granules of sphene, and occasional small crystals of apatite are also usually present. Most of these diabase homfelses are banded, certain folia being rich in hornblende, others in augite or felspar, etc. When felspar occurs in any quantity it forms the matrix of. the rock, and when its crystals are large (3 or 4 millimetres across) they are filled with prisms and needles of hornblende, irregular flakes of mica, iron ores, etc. When the felspat is in smaller grains, these may show indistinct traces of crystalline form or may compose a very fine mosaic of irregular indi- viduals. The hornblende may be aggregated into bands or form centric groups, or may be scattered quite irregularly through the felspar. In some rocks the biotite, augite, and hornblende occur in rounded knots. Augite, when in small grains, forms bands, streaks, and indefinit© patches surrounded by felspar or hornblende. Pneumatolytic Modifications of the Greenstones. Like the other rocks around the granite the greenstones show indubitable effects of the fluoric and boric vapours, which passed out through them along fissures and joint planes. But as these rocks are comparatively rich in lime, and as their larger cavities were probably occupied by calcite, chlorite, zeolites and other secondary minerals, we may expect to find in them a totally different set of minerals from those fui*nished by the granite and the slates (both of which are remarka;bly poor in lime-bearing minerals). As a matter of fact, tourmaline is not the commonest pneumatolytic deposit, and topaz is not known in the greenstones. These are replaced by axinite (a boro-silicate of lime and alumina) and fluorspar. Axinite is the characteristic mineral of the pneumatolytic veins of the greenstones. Along with it occur epidote (yellow or greenish), GREENSTONE. 39 pale-green augite, green hornblende, a little felspar, brownist garnet, iron ores, and occasionally zincblende. Sphene, fluorspar, apatite, and pyrites are also known in tbis associa- tion. The axinite is violet in the hand specimens but colourless or of a feeble violet tinge in thin section, with weak pleo- chroism. It is idiomotphic only when lining the walls of druses. The augite is seldom idiomorphic and is of pale- green colour, sometimes weathering to dark-green uralite. The epidote is pale-yellow, often zon.al, very closely resembling the augite in certain sections ; its dichroism is feeble. The garnet is usually brown in the hand specimen, and though sometimes in dodecahedral crystals is more generally irregular. It is usually doublyref racting, showing sectors or zones of dark-grey colour between crossed nicols, and occasionally each external face corresponds to the base of a triangular segment, the apex of which is situated at the centre of the crystal. It is the least common of all the minerals mentioned, but is found in con- siderable amount on the west coast near Botallack and Levant. Fluorspar is not frequently seen and is never abundant. Felspar occurs more frequently and is usually simply twinned or un twinned alkali felspar. Green hornblende, in large prisms with characteristic cross sections, occasionally is far more abundant than the augite, while the brown hornblende of the diabase hornfelses is never seen. Brown biotite also is absent from the rocks under consideration, but a pale-green chlorite is not uncommon. Tourmaline may occur in small pale-blue needles in the axinite, and at Penlee forms veins with epidote, chlorite, augite, and alkali felspar. It is there of an extraordinarily deep-blue colour, highly pleochroic (pale- violet to blue-black), beautifully zonal, and idiomorphic in transverse section. In other cases part of the tourmaline is dark-green. Sphene is also a frequent mineral. This distinctive mineTal association or paragenesis is known not only in the Land's End area but in all districts of Cornwall where the granite has invaded the greenstones. It is found in veins, nodules, and irregular patches, mostly quite close to the margin of the granite, but also occasionally at some distance from it. The deposits are not nearly so common as the quartz and tourmaline rocks of the tin veins, and though sometimes metalliferous, are not rich or widely worked. The axinite, fluorspar, and tourmaline prove the influence of the vapours discharged from the granite ; all the other minerals, excepting the chlorite (which may be really secondary), are such as may be -formed at comparatively high temperatures, and they are nearly all. compounds in which lime plays an important part. Particulars of other occurrences will be found in the Geo- logical Survey Memoirs on Newquay (pp. 25-29) and Truro (pp. 47-5.1). The best localities for axinite rocks in the area undter description are Chyandour, St. Ives Island, Chenhalls, Carrick Du, Levant, and Botallack. 40 CHAPTEll IV> GEANITE. Grranite appears at the surface over more tkan half the area described in this Memoir. The main mass, forming the principal high ground, occupies nearly all the Land's End district proper; that is to say, the upland Region west of Penzance and of the wide open valley which stretches to St. Ives Bay, This mass, though somewhat cut into by the sea, is fringed with sedimentary rocks in such a way as to show that its original limits southward and westward cannot have been far from the present coast-line; the outline shown by the cliff must, therefore, coincide very nearly with the original boundary of the granite. Another mass occupies about five square miles between Godolphin Hill and Trewavas Head, where it is cut ofi by the sea. But in this case also the original limit must be nearly complete, for part of the fringe .of sedimentary rock still clings to the steep southward slope of the granite at Rinsey. A third much smaller exposure of granite occurs at St. Michael's Mount ; but this is cut off by the sea on three sides. The narrowness of the metamorphic aureole on the north, and the comparative small intensity of the metamorphism close to the granite, suggest, however, that this was a small boss, unconnected near the surface with any larger area. "When these various masses are studied more closely, it is found that though the granite is always of the usual type found in Devon and Cornwall, yet there are slight differences between the isolated masses, and even more striking differences between earlier and later intrusions within the same mass. Tlie rock, whether coarse or fine grained, in its unaltered state may be described shortly as a muscovite-biotite granite, with large crystals of orthoclase and rare crystals of pinite and . tourmaline (schorl), the amount of muscovite and tourmaline increasing greatly in certain areas and in the neighbourhood of certain lines of fissure. Over large tracts the alteration has gone much further, so that the felspar has been partially trans- formed into kaolin ; but in this particular region only limited areas are fit for working as china-clay. The main granitic mass occupies about half the map and forms the bold cliffs of the Land's End. It will be convenient to commence the description of this area with the large quarries of Lamorna, where the stone has been extensively raised for export, and is apparently less altered than usual. These quarries lie about four miles south-south-west of Penzance, on the north-east side of Lamorna Cove. They are close to the sea, and it is only the-great difficulty of shipping the stone that prevents the quarries from being more extensively worked. Lamorna is of little use as a harbour, and the stone has to be carted to Penzance. GRANITE. 41 The granite of Lamorna is coarse grained, with very large crystals of orthoclase, which lie in all directions, thus adding to the strength of the rock, but not helping it to split along any particular line. The colour is grey, with paler-grey or nearly white porphyritic crystals, the greyish colour of these orthoclase crystals being due to inclusions of dark mica, often forming narrow zones. The occurrence of numerous dark- coloured fine-grained patches, commonly several inches in length, somewhat spoils the appearance of the stone, though they do not seem in any way to affect its toughness. Midway between Lamorna and Penzance will be found the Sheifield Quarry, in the parish of Paul. Here the coarse- grained granite is very like that of Lamorna, except that there is a decided tendency for the large felspar crystals to lie in one direction, thus somewhat altering the appearance of the stone. This orientation of the crystals parallel to the direction of movement in the still viscid granite is often very conspicuous towards the outside of the granite mass. Where it is seen away from the margin it can probably be taken as an indication of the former proximity of the sedimentary rocks overhead. Orientation of this sort necessarily helps to determine the direction of the jointing in the mass, and where it is con- spicuous we commonly find dominant low-hade joints parallel to the longer axes of the crystals, thus adding to the pseudo- bedded appearance of the granite. It must not be imagined, however, that this 'bedding^' can be studied in a hand specimen; it is noticeable on viewing Et earn, cliff, or quarry- face from a little distance, giving a streaky look to the rock; but in a hand specimen only two out of three, or three out of five, crystals will point in one direction, and this, of course, might be accidental. A third large quarry is now being worked in this coarse- grained granite, at Newmill, in the parish of Gulval, where large blocks are raised and sent away for dock-work. There is also a fourth quarry, somewhat smaller, at Zennor, by the St. Ives, road, about a quarter of a mile east of the village. Here the stone is split into gate-posts, kerbs, etc., or used for building in St. Ives. All these quarries are in stone of similar type and coarseness, the rock varying principally in the presence or absence of the bedded structure, or in slight differ- ences of colour. In each of these quarries occasional felspar crystals are found twinned in the form of a cross, and these are collected and sold by the quarrymen as curiosities — they were formerly thought to have peculiar virtues. • Though numerous small quarries have been opened for local use, those above noted are the only ones of importance, and it must not be imagined that any large part of this extensive area of coarse-grained granite would be fit for quarrying for export, even if better facilities existed for shipping the stone. Much of the granite is very rotten, either through surface weathering or through changes caused by hot vapours and solutions ; other parts are so penetrated by veins or segregations of finer-grained granite as to make the texture very uneven ; 42 GEOLOGY OF LAND's END. areas near lodes or schorl veins are quite useless for large blocks, for the rock is always much altered in their vicinity, and is usually cut up also by irregular joints. The margin of the Land's End mass, though of little economic value in itself, is of great interest for the phenomena of metamorphism associated with it and for the development near it of the various mineral lodes which have been of so great value to Cornwall. The lodes will be spoken of in a later chapter; some of the metamorphism has already been described ; here we will trace the margin, point out the general character of the contact at different spotsj and indicate where the best exposures are to be found. From Newlyn southward, gradually increasing metamor- phism is noticed as Mousehol© is approached. 'No granite veins are seen on the foreshore till we are close to the margin of the main mass, though one large vein appears in ^ quarry east of Paul Church. This quarry lies apparently about a quarter of a mile outside the main granite boundary, and it appears to be surrounded by red and green highly altered schists, though no junction is visible. In St. Clemiplit's Isle a single two-inch vein of granite has been found. The best exposures are on the foreshore at Mousehole, where the margin of the granite, sending out numerous irregular veins, is excellently laid open. We notice first, immedi- ately south of the harbour, a long, almost straight parallel-sided eight-inch dyke of black schorl rock, which runs direct from high water- to low water and does not follow the direction of cleavage in the slate, here about north-north-east. Its connection with the granite is not visible ; but judging by its behaviour and by other similar veins elsewhere, it is of somewhat later date. A few yards south of this narrow dyke tongues and irl'egular inosculating veins of coarse porphyritic granite make their appearance, and become closer and closer together till they merge into the main mass. In one or iwo cases these veins pass into fine-grained rock at their narrow extremities ; but more commonly they are coaTsely porphyritic right up to the junction with the slate, as is the mass of the granite. One vein was interesting as suggesting that in some cases at least fine-grained veins may be the result of a purely mechanical straining action, for towards its narrow extremity a large crystal of otthoclase had become fixed across, so that it was jammed against the slate on either side. The removal of the large crystals by such action, when the molten rock passed through narrow fissures, might lead to noticeable differences both in composition and appearance. This point will again be referred to m the chapter on elvans. Between the Mousehole Cave and Lamorna the cliffs show massive coarsely porphyritic granite of the ordinary type ; but the seaward slope of the bedding-joints, and the conspicuous tendency to orientation in the same plane of the large crystals, suggest that the margin is not far away. This seaward dip causes blocks to slip away, so that here we find a riigged steep slope, with only a comparatively low vertical cliff at its base. GRANITE, 43 The vertical cjiff does not exceed a hundred feet till Carn-du is passed and the direction of the coast changes. The coarsely porphyritic granite near the junction, with the greenstone which rests upon it at Tater-du, is described by Mr. Wilkinson as showing numerous dykes of finer-grained rock, some of which penetrate the greenstone. This contact has already been alluded to in Chapter III. As it is traced westward the granite loses its seaward dip and the cliffs rise in height, till near the Logan Rock they exceed 200 feet. The Logan Rock is a earn of granite, the uppermost block of which has the comers and edges so rounded and weathered that the mass is now poised on a single point. Though, weighing many tons, it can be rocked, "with difficulty, by one man. There is no need to describe in detail the cliffs towards the Land's End. The horizontal and vertical jointing cause them to form bold castellated crags, rising to a height of 200 feet (see Plate I.). They show numerous veins of finer granite, which often are not sharply differentiated from the surrounding coarse-grained rock, tfust north of the Land's End much of th« granite is less coarsely porphyritic than usual, and the crystals are scarcer and more irregularly scattered. The stone some- what resembles that of Gulval Down, but cannot be separated from the general mass. At the Longships the margin of the granite is again met with, though in a most inaccessible place, for while the light- house' rock itself consists of much-altered slate the inner rocks consist of granite. Whitesand Bay seems at first sight to be a singular feature to find on a rocky granitic coast, all of which is equally exposed to the Atlantic surf. Perhaps, however, the existence of the bay is explained by the close proximity of the softer killas. Dr. Forbes records that at the western extremity of the bay " there is a small patch of the slaty felspar rock [hornfels], laid bare at low water, of about one hundred yards in breadth. It is seen in immediate contact with the granite. . . . Large veins of granite, varying in the character of its constituent parts, traverse the slate in all directions, while patches, if not veins, of slate are, in turn, confusedly strewed through the granite. This small bed dips north at a very small angle ; but, indeed so little of it remains on the granite, that its dip can- not be very correctly ascertained. There is another smaller patch of slate a few hundred yards to the westward of Sennen Cove, at the foot of Pedn-men-du Point."* It is not absolutely clear whether these patches may not be merely large inclu- sions in the granite ; but inclusions of this size only occur close to the mairgin, and their occurrence seems to show that the floor of the bay is probably slate or greenstone, and not granite. It will be noticed that all round this coast there is a tendency for the hard inner zone of the metamorphic rocks to form a * 'On the Geology of the Land's End District,' Trrnis. Soy. &eol. Soc. Com., vol. ii., 1822, p. 264. 44 . GEOLOGY OF LANd's END. belt fringing the granite, while the outer and softer zones are cut away by the sea. The granite cliffs between Whitesand Bay and Cape Corn- wall suggest that the margin is not far off, for the bedding- joints and the large felspar crystals tend to dip westward. This dip, however, is not so marked as to cause landslips, and where it becomes less directly seaward, opposite St. Just, the height of the cliff rises to 300 feet. Perhaps the numerous subsequently formed bands of greisen in the mining area may also help to hold the crags together and make the frac- tures more vertical. Cape Cornwall shows excellently the junction of the granite with -the slate, especially in the little bay known as Priest's Cove. The granite is of moderately coarse grain and much, tourmalinised, narrow veins of schorl rock often expanding into small nests of black coarsely-crystallised tourmaline. The granite veins which penetrate the highly-altered slate are of the usual irregularly inosculating type. In this they contrast strongly with the straight parallel fissures and dykes which characterise later stages, during which the bands of greisen and the tin lodes were being formed and the elvans were being intruded. From Cape Cornwall northward to Pendeen, across the St. Just mining district, the granite boundary for some distance runs about a quarter of a mile inland, and parallel with the coast. No granite veins are seen in the cliff; and this shows that it must be quite exceptional foi- a vein to penetrate 400 yards into the surrounding l-ocks, otherwise some would be met with. The junction of the granite and slate is crossed again and again in the mines, and Fig. 14, p. 109, from a section of the Levant Mine, shows the nature of the junction, as proved in numerous levels, one above another. It may be remarked that these sections, supplied by mine plans, seem to ignore all veins, and take only the contact with the main mass. The junctions in this mine, which are proved to a depth of about 1,600 feet below the surface, are irregular ; but they suggest a double curve, the upper part turn- ing over to complete the roof of the dome, the lower part becoming less steep as it approaches the level of the buried floor of granite, which probably extends westward to Scilly. Where the boundary again strikes the coast, at Porthel'as Cove, it is a good deal obscured by head and by beach ; but granite veins can be seen to penetrate the slate. The granite on the east side of this cove is coarsely crystalline, and contains a good deal of pinite. Coarsely porphyritic granite, often with much schorl, forms the cliff for the next two miles. Porthmeor Cove exhibits excellent exposures of the junction of the granite with the surrounding rocks, many veins of granite penetrating the greenstone and slate. The junction of the main mass of granite with the mixed greenstone and slate is well seen, and appears to be very steep, though this extreme steepness is apparently quite local. The granite in places is coarsely porphyritic up to the junction with the older GKANITE. 45 rocks into which, it sends tongues ; it contains also veins of finer-grained granite, which cut through both the coarse granite and the greenstone. Bands of greisen cut through both granites and are numerous; bands of schorl rock cross everything, though they become inconspicuous in the green- stone. Rare inclusions of killas occur in the granite, and extend a few yards from the junction. The granite veins on the north-east side of this cove are worth close study, for they are easily examined on a shelving surface of clean bare rock. iVo of them have been photo- graphed by Messrs. Gr. V. and H. Preston, whose photograph has been reproduced in the third issue of the Geological Photo- graphs Committee of the British Association (No. 2,880). A photograph taken by Mr. T. C. Hall is reproduced in Plat© III., at the end of this Memoir. In this neighbourhood some of the veins inosculate; others cut and shift each other, as in the example photographed. The rock into which these particular veins are intruded is a knotted hornfels, one band of which yields small perfect garnets. At Porthmeor the boundary again leaves the coast for a couple of miles, returning to it immediately north of Zennor. The sections between Porthzennor Cove and Wicca Pool have been described a^gain and again, for they are some of the finest in Cornwall, illustrating the mode of intrusion of the granite into the slate and the intricate way in which the tongues of granite cross and inosculate. A good illustration of the behaviour of the granite veins at Wicca Pool is given by De la Beche.* East of Wicca Pool the boundary again leaves the coast ; but granite veins are still occasionally to be seen in the cliff, and north of Trevalgan an exceptionally large vein forms a granite inlier about a quarter of a mile from the main mass. This inlier is of great interest, for the granite in H has altered into a mass of schorl rock, without mica, and with little felspar remaining. The rock shows now a black matrix consisting of schorl and quartz, in which are clearly recognisable the original large porphyritic crystals of felspar ; for these latter havfe been replaced by a paler-coloured mixture of quartz with a little schorl. Were it not for the perfect preservation of these pseu- domorphs it might be thought that this rock was merely a vein-stone. A tin mine was once worked at this spot, and the spoil from it yields abundance of large blocks of the altered granite ; at present there is no section visible of the granite in place. It may here be remarked that this type of alteration is very prevalent between Trevalgan and Halse Town, the walls yielding abundant specimens of these jDseudomorphs, thiough, the mines being now closed, it is impossible to collect from the rock in place. The eastern border of the granite calls for little remark, as it is not well exposed, though there is siifficient evidence to enable us to trace the line with a fair amount of accuracy. * ' Geological Report,' Plate V, 46 GEOLOGY OF LAND's END. The dip cannot be tigli, for the granite seen in the ravine above Crowlas can be proved to run for some distance beneath the killas, and a level driven into the hill at Nanceddan was in granite all the way, till it reached a shaft sunk in the green- stone quarry above. This part of the granite border is only sparingly metalliferous, and the mine just mentioned obtained no tin, though we are told that wolfram, was found, and thrown away before its value was recognised. Around Madron, also, the dip of the granite surface seems to be unusually low. Not only" is the aureole of metamorphism exceptionally wide, but the behaviour of the boundary. where it crosses valleys suggests a gentle dip. At Hendra there is trace of a granite vein more than a quarter of a mile from the border; half a mile to the south-west an outlier of greenstone rests on the granite in such a way as to suggest a dip not exceeding 30°. The main valley through which the Penzance and Land's End road passes ought to show the nature of the border; bnt the actual junction is so obscure that it is not clear whether the curious right-angled turn shown on the. map may not be the result of a fault. It has been found that the Land's End mass is not all of one age or type, but includes an area of about seven square miles of a fine-grained granite of somewhat later date, which extends from Gulval Downs nearly to Zennor on the north, and from Amalebrea to Camaquidden on the west. This granite is so fine grained that it is commonly known as ' whetstone ' or ' sandstoae ' ; but its composition is similar to that of the coarse granite into which it is intruded. It is a buff or grey biotite granite with small (half-inch) scattered crystals of orthoclase, and rarer crystals of pinite of about the same size. Its boundary is sharply defined, but there is no section showing the actual junction of the two rocks, though at its northern limit at Beagleton Downs loose blocks on the moor show numerous veins of this fine granite, penetrating coarse granite of the common Land End's type. The newer granite forms undulating land, surrounded by tors or earns of the coarser type, but itself neither forms earns nor weathers into large rounded masses like those which nearly everywhere encumber the ground outside its limits. The farmers consider the land to be of better quality ; but it could not be ascertained cleariy whether this was due to any difference in the composition of the soil, or merely to the greater convenience for working where large boulders are absent. Much of Penzance is built of this fine-grained rock, with dressing of the ordinary coarse granite. Thus far, only the buff rock near the surface has been used to any extent, but below 15 feet the Castle-an-Dinas Quarry shows an ex- cellent giiey stone, which ought to be of considerable value. The Gulval Downs rock, however, does not split in the same wav as the older granite, and appea;rs never to be used for lintels or gateposts, . even close to the quarries. It is used. GRANITE. 47 locally for road metal, and is better than the coarse granite, but not equal to the greenstone. This granite is best seen in the Castle-an-Dinas Quarry, where much of the stone used in Penzance, Marazion, and 8t. Ives has been obtained. The rock is a fine-grained, slightly schorlaceous, granite, with small porphyritic crystals oi ortho- clase, and a few of pinite; it is little altered and without schorl veins. In one place the floor of the quarry is traversed by a tongue of coarse pegmatite, somewhat more schorlaceous. Till lately, only the upper warm-coloured stone was quarried, as the owner would not allow the depth to exceed 15 feet. Now the quarry is being opened at a lower level, where the rock is grey, harder, and can be used for curbs, etc. The joints seem to be further apart, and the granite is obtainable in larger blocks than in the other quarries in this stone. The Gulval Downs Quarry is a quarter of a mile to the west of the one just described. The stone is almost identical with that of Castle-an-Dinas. It works easily, and has been exten- sively used in Alexandra Eoad, Penzance. A third quarry in the same neighbourhood is the Ludgvan Parish Quarry, at Inch's Castle, worked for road metal. This quarry is within 200 yards of the boundary. The stone is fine-grained, very schorlaceous, somewhat tougher, and is apparent altered rock in the neighbourhood of a vein or lode. This schorlaceous altered nature of the marginal rock is just as characteristic of the fine-grained as of the coarse- grained granite; but there is also another schorlaceous belt surrounding the China Clay Works of Bohemia. Besides the large area already described there is another intrusion of the fine-grained granite not far from Carbis Bay, where it forms the narrow ridge, on which is placed Knill's Monument. This mass is about half a mile long by 70 yards wide, its longer axis striking north-west. It was at first thought to be an elvan of exceptionally granitic character; but there seems now to be little doubt that it is an altered granite, originally much like that of Castle-an-Dinas. Its junction with the surrounding coarse granite unfortunately is not now exposed. The rock, as seen in the spoil heaps of the Providence Mine, is a fine-grained mixture of quartz and felspar, with a few one-inch porphyritic crystals of ortboclase, a little btown mica, schorl, and white mica. Scattered irregu- larly, are crystals or nests of black mica and schorl, both minerals projecting freely into small cavities. Several quarries in the same granite, further from the margin, are to be seen on the north-north-west side of Knill's Monument, between the two woods. The granite here is slightly coarser, but very similar. It contains pockets of ' giant granite,' or pegmatite, composed of quartz, ortho- clase, and schorl, the two latter in very large crystals, which seem to interlock. In these quarries the flat surfaces of close joints exhibit rosettes of schorl needles, which, though appar- ently subsequent to the consolidation of the granite, yet indent both the quartz and the porphyritic felspars. No secondary 48 GEOLOGY OF LAND's END. quartz seems to accompany these rosettes, the only contem- poraneous mineral observed being rare flakes of specular iron ore. The next granite area to be described is the small mass of St. Michael's Mount, long famous for its display of contact phenomena, for its intrusive veins, and for its minerals. This fame is largely due to the peculiar position and accessibility of the Mount," for as far as the granite veins and the minerals go, they are even better seen around Zennor and near Cape Cornwall. The point, however, in which St. Michael's Mount excells all others, is in the fine development of parallel bands of greisen, often with topaz, which are here better seen than any- where else, except at Cligga Head, near Perranporth. The granite of St. Michael's Mount is somewhat fine-grained, but differs in appearance from either the coarse or the fine variety in the Land's End mass. It is a good deal altered, so that it does not form a good building-stone. None is quarried now, as the- whole Mount is in private grounds. The granite foreshore on the east side of the Mount, near the junction with the slate, shows a striking series of parallel vertical joints, up which hot vapours or solutions have travelled, and on each side of these joints the granite has been altered for several inches into ' greisen ' or mixture of quartz and white mica, with a certain amount of topaz. These bands of greisen are sometimes so close together that there is scarcely any unaltered rock between ; but the maximum alteration is always in close proximity to a vertical fissure. These fissures are really lodes ; though here they only contain a little ore. Fine crystals of cassiterite are found, and the other minerals include ores of tungsten, uranium, zinc; apatite and topaz occur also in crystals of considerable size. Even as far back as 1819 Dr. John Forbes pointed out that these particular greisen bands (or quartz veins as he called them) were merely varieties of the schorl-rock veins such as occur at the Land's End* ; every intermediate variety can readily be found. The granite of Godolphin, Tregonning Hill, and Trewavas Head forms comparatively high ground, which, at one point, reaches 635 feet above the sea, though most of it does not exceed 400 feet. The rock is variable, somewhat coarse- grained, but commonly without many porphyritic crystals, or with porphyritic crystals of moderate size. It has undergone great alteration, and is worked in various clay-pits. The extensive kaolinisation makes the stone soft and rotten, and this is the cause of the relative lowness of the gl'ound, which is not nearly so high as we should find in unaltered granite. Where the granite first appears in the cliff and on the fore- shore, at the east end of Prah Sands, its margin is strikinglv bedded, showing alternate bands of fine-grained rock, and of rock with large, short crystals of orthoclase. The short- ness and stoutness of these crystals makes them look very * • On the Geology of St. Michael's Mount.' Trans. Roy. Geol. Hoc Com vol. ii. 1822, p. 366. GUANlTfi. 49 ^ilulike tk© ordinary porphyritic crystals in tke granite. Tke bands may be later intrusions of pegmatite; but the lairge crystals do not interlock in the way seen in the pegmatite veins of Castle-an-Dinas.. A few granite veins penetrate the slate, and these are exceptionally micaceous, one vein seen on the foreshore being composed almost entirely of mica. No vein of sufficient size to be worth working for lithia was observed. Near Rinsey a mass of killas rests on the granite with a steep seaward dip, the granite beneath showing distinct fluxion structure. The coast at Tremearne shows exceptionally fine examples of granite veins penetrating the killas. These veins are of un- usual character, forming large and approximately horizontal sill-like masses. Here, again, the smaller veins are excep- tionally micaceous; they yield also a good deal of fluorspar. The inland exposures of this mass call for no remark. The rock is fairly sound in some of the quarries at Tresoweshill, and at Godolphin Hill; but elsewhere it has been too much affected by the action of hot solutions from below to be of much value as a building stone. The varying width of the aureole of metamorphism suggests that towards Tremearne and Porthleven the underground slope of the granite surface may become very slight, for in that direction the aureole widens from an average of a quarter of a mile to fully three-quarters. To the north of Godolphin Hill also the, outer zone of the aureole seems to be connected in some obscure fashion with the isolated metamorphic areas which extend northward to Gwithian. It looks as if the granite of Godolphin Hill plunged beneath the siirface at a high angle, and merged into a nearly horizontal undulating sheet at a considerable depth. Peteological Desceiption. The coarse-grained granite with large porphyritic crystals of felspar, which is the prevailing type in the Land's End mass, is usually much weathered at the surface, and fresh specimens can only be obtained in the deeper quarries, such as Lamorna. The large felspars give it a very characteristic appearance; they do not weather out as the matrix crumbles down and consequently theit crystalline forms are not readily ascertained. Their distribution in the rock has been alreadjr described and their frequently parallel orientation, which indicates that they were very early products of crystallisation and were swept along by currents in the liquid granite at a time when a large part of the l-ock was in a perfectly molten and fluid condition. The tendency to assume a position with their flat surfaces parallel to the margin of the overlying killas is well, seen in many quarries and coast sections and is verv instructive. The other potphyritic minerals are cordierite (pinite) and quartz. The former of these is very widespread, and its pseudomorphs having a dark-green coloui- and platy structure, together with 956t ^ 50 GEOLOGY or land's end. the more or less perfect form of a kexagonal prism, are readily observable. Porphyritic quartz is usually not so conspicuous to the eye, but near the edges of the granite, in such localities as the coast near Tater-du, where the soft decomposing matrix is eroded by the sea, the larger quartzes stand out conspicuously on the rock siirface. The large felspars are often three or four inches long, and in cross fracture show simple (Carlsbad) twinning, each half of the crystal having a different lustre when the light is reflected from them. Specimens five inches long are not uncommon, and the largest which we have seen measured seven inches. The pinite is usually from one-half to one inch in length, and the quartz less than half an inch across. Biotite and tourmaline form small black specks in the hand specimens (the former easily distinguished by its softness), and silvery-white flakes of muscovite are also easily detected. In microscopic section the felspar is always slightly turbid, owing to incipient decomposition, which has produced minute flakes of kaolin and muscovite scattered through its substance. The milky, white, semi-transparent appearance in the hand specimens arises from this. The large porphyritic crystals consist of a matrix of dull orthoclase traversed by exceedingly fine veinlets of clear transparent albite (perthite felspar). They are not zoned, though they may contain inclusions of mica, oligoclase, etc., zonally arranged. At their outer edges they merge into the surrounding granite, as, though early, formed, they have continued to grow till a late period in the history of the rock. Hence their crystalline faces are rough, and they do not easily separate from the granite when they weather. They are always flat plates, their principal face being the clinopinakoid, while the basal plane, prismatic faces (110) and orthodome (101) are also commonly recognisable. Carlsbad twinning is practically universal, but other types of twinning are rare. The large twins above referted to, which have in section the form of a Maltese cross, cannot be detached from the granite matrix and accurately measured crystallographically. They consist, however, of Carlsbad twinned individuals, and from the disposition of theit cleav- ages, seem to bef penetration cross twins on 111, though some may have 021 as their twin plane.* Their commonest enclo- sures are small, perfectly idiomorphic crystals of a soda-lime felspar, which has the optical properties of oligoclase-albite. Black mica, zircon, and apatite also occur in them, and often a considerable amount of quartz in small rounded or angulat patches, which are, on the whole, most common near their outer edges. iTf ' In the granite matrix the felspar is abundant and belongs to both varieties enumerated above. Oligoclase (and oligoclase- albite) is the less important of the two. It is a comparatively early mineral. It is often zonal, the outer deposit being more acid than the central part of the crystal, and its crystals are 'Laspeyres, ifeita. Xryitallogra^hie^ I., 344, 1877. GRANITE. 51 usually well formed, but the more abundant perihitic orthoclase of tbe matrix occurs only in grains of irregular shape. Kaolin and muscovite increase in amount in these felspars as decomposition advances : very frequently also their turbidity is caused by the presence of very numerous minute fluid cavities of tubular or elongated rectangular shape. Microcline is very rarely to be seen in the granites of this area, and felspars more basic than oligoclase do not occur. The quartz calls for no special remark except that it affords an exceptionally good opportunity for investigating fluid cavities, as these are very numerous and large with mobile bubbles and often also small cubical or elongated colourless crystals. While most of these cavities are quite irregular, many of them are ' negative crystals ' bounded by faces corresponding to those of quartz crystals. The white mica or muscovite of the granite is usually in small shining flakes which rarely have any trace of crystalline outlines. Occasionally it contains small zircons, and around these there may be greenish pleochroic halos. The black mica is reddish-brown in thin section, changing to pale, clear yellow when the polariser is rotated. Its pleochroic halos around enclosed zircons are numerous and pronounced, becoming black when the ray of transmitted light vibrates parallel to the cleavage. It has a small axial angle (about 10° or 12°), and though it does not colour the blow-pipe flame strongly red it gives a marked reaction for lithia when examined with the aid of a pocket spectroscope. Hence- it must be grouped with the lithionites or lithia micaSj which, as Sandberger has shown, are so characteristic of the tin-bearing granites. The white mica also proves to contain lithia, but is otherwise a typical muscovite with wide axial angle. Very often the two micas are clustered together or intergrown in definite parallel growths with their basal cleavages corresponding. The lithionite weathers some- what readily to dark-green chlorite mixed with rutile; the muscovite remains perfectly fresh, and, in fact, its amount is increased by the formation of small secondary flakes in the alkali felspar, only distinguished from the primary muscovite by their distribution, their small size, and their ragged forms. These arise independently and are not deposited on the surfaces of the primary crystals. Another mineral of prime interest in the Cornish granites is tourmaline. It shows an extraordinary diversity in its forms, colours and associations, but the tourmaline of the normal or unmodified granite is practically always some shade of yellow or brown and strongly pleochroic. Small dark halos are common in it and zonal structure also is frequent. The crystals are usually rude, though not unfrequently the trans- verse sections are sub-trigonal. There is often an imperfect basal parting and occasionally longitudinal cracks corre- sponding apparently to the boundaries of prisms in parallel growth, but the smaller grains are quite irregular in outline and devoid of cleavage. It is never decomposed. Much of the tourmaline is primary and belongs to an early stage of B 2 52 GEOLOGY OF LAND's EOT). crystallization, as it encloses only apatite and zircon and very rarely small crystals of felspar. Of th.e accessory minerals, apatite is the most common, usually as shapeless grains, which may be half a millimetre in section and are quite colourless. Well-formed, short, hexagonal prisms also occur, especially in association with the mica. Zircon is always present, and there are also frequently very minute crystals, seemingly opaque when vety small, but showing a faint line of light towards their centres when they are of greater size. These, as suggested by Rosenbusch,* may be cassiterite, and the presence of this mineral in the Dartmoor granite has been suspected by Busz,t but it should be noted that tinstone in crystals of fair size is not difficult to identify, and certainly occurs only in the granite and its modifiations in the neighbourhood of mineral veins or other fissures. The finer-grained granite of the interior intrusions and of the veins which ramify through the coarser variety presents little essential difference in mineralogical composition from the main mass. Its phenocrysts also are perthitic orthoclase; the matrix has very much of the structure of an aplite, from which rocks the paler, fine-grained, non-porphyritic types are indistinguishable. A greater abundance of oligoclase-albite, however, is often noticeable, and tourmaline also is more frequent, while biotite diminishes in amount. Oordierite (pinite) is of very common occurrence in these fine-grained rocks, and topaz is even more characteristic of them. If a few slides be examined, topaz can always be detected, and often there are five or six crystals in a single microscopic section. Andalusite is probably more frequent in the coarser-grained rocks. The cordierite, so widely disseminated through the Land's End granites and elvans has never been observed in a fresh state. + It presents the form of six-sided prisms, which range up to an inch in length, and have a well-marked cleavage parallel to the base. These prisms are no doubt the remains of crystals which were twinned on the plan usual in cordierite and consisted • of three sub-individuals. Microscopically examined, they prove to consist of white mica and of chlorite in varying pro- portions and arrangement. Commonly the white mica has its basal cleavages parallel to the flat ends of the pseudomotph. It forms continuous bars which cross the aggregate at ehort intervals (like the bars of a window), and it also fills up the spaces between these bars partly in well-defined plates, which have a parallel orientation to the mica in the bars, and partly in a dense feltwork of minute fibres irregularly disposed (see Plate VI., Fig. 1). The chlorite is dark-green in hand speci- men, pale-green in section, feebly pleochroxc, and gives usually low grey or brownish polarisation tints. It lies mainly in the interspaces between the bars, and is sometimes well crystallised » ' Mikroskopisohe Pliysiographie,' vol. i., part 2, p. 56, 1905. t Neites Jtt'^ h.fur Mineralvgie, B. B. xiii., p. 98. j Fresh cordierite has been found in the granite of Gready, Luxullian, by Prof. Bus?. Uep. Brit. Assoc, for 1904, p. 564. GRANITE. 53 and orientated parallel to tte mica ; at other times scaly and mixed with: the felted muscovite. Both topaz and andalusite are of common occurpsnce in the Land's End granite ; the andalusite in all varieties of the rock, the topaz principally in the finer-grained granite of the dykes and central masses. Both form only small crystals, less than half a millimetre in diameter as a rule^ and not visible to the naked eye, and though they are not usually to be found in the same rock slide, each of them tends to occur in small clusters. Their crystals are imperfect and rarely show traces of crystal- line faces. They present few features of mineralogical interest ; the andalusite may be colourless, but very generally shows distinct though faint rose tints when the polariser is rotated. The topaz is rendered conspicuous by its perfect basal cleavage and its rather high refractive index. It is generally free from the branching fluid cavities which are found in certain Saxon and Bohemian localities. Examples of andalu- site-bearing granites are Lamorna, Zenno'r, and Newmill, while topaz occurs at Lesceave Por (near Trewavas Head), Knill's Monument, and Sennen. The unaltered or normal granite, except for its varying coarseness of grain, is remarkably homogeneous and uniform over wide areas. The absence of basic facies, which might be supposed to have originated by magmatic differentiation, is practically complete. Black spots occur frequently, and have a deteriorating effect on the quality of the stone for ornamental uses. By far the greater number of these are enclosures of altered slate (' hornfels '), but a few are early segregations composed mainly of biotite, muscoyite, apatite, zircon, and iron oxides, with a small amount of quartz and felspar. Towards the margin of the granite, or irregularly dispersed through its outcrop, veins or patches of coarse pegmatite occur, consisting of large crystals of perthite, muscovite, tourmaline, and quartz. Eluorspar and gilbertite are also common in these veins, and Mr. Scrivener has shown (in ' Geology of Wewquay,' p. 45) that they may contain large well-crystallised iopazes. Veins of this kind are excellently exposed on the shore at the west side_ of Trewavas Head. Fine-grained, non-porphyritic tourmaline granites and aplites also occur as veins intersecting the granite, and in the locality above mentioned they may be seen pene- trating and splitting apart the pegmatite veins. Hence both of these are later than the consolidation of the granite in which thev occur. The ' Pnel'matolytic ' Modifications of the G-kanite. Both, from a practical and from a scientific standpoint these are of great importance. Towards the margins of their out- crops the Cornish granites are in most cases encircled by rocks which are rich in tourmaline, quartz, and whit© mica. In this belt the workable tin deposits are situated, and there can be no doubt that the introduction of the tin ores was con- temporaneous with the alterations which produced these 54 GEOLOGY OF LAND's END. peculiar rocks.. In this belt three types are to be dis- tinguished : (a) the edge of the granite itself has been converted into schorl rock (quartz and tourmaline) or into greisen (quartz and white mica) ; (6) the surrounding sediments (killas) have been impregnated with tourmaline, and 'tourmaline schist' has resulted, or, more rarely, have been filled with white mica also (tourmaline muscovite schist) ; (c) in the fissures of the granite and of the sedimentary rocks deposits of quartz, tourmaline and chlorite have been laid down. These last are the typical tin veins, but tinstone may occur in any part of this altered zone. It is generally admitted that the agents which occasioned these changes, were vapours emanating from the granite at a time following its injection but anterior to its complete cooling and consolidation. These vapours consisted mainly of water at a very high temperature. The occlusion of water in molten igneous magmas is a phenomenon of universal occurrence and needs no special explanation in this connection. But it is clear that- the Cornish granite masses discharged not only steam, but other substances which have the power of profoundly modifying rocks when they penetrate them, especially at high temperatures. Compounds of boron and fluol-ine were certainly present, as these elements are specially characteristic of the new minel-als deposited (tourmaline, topaz, mica, fluorspar). Lithia and phosphoric acid are other substances which passed outward from the granite. Finally, most of the metalliferous ores may reasonably be ascribed to the same source. This is established beyond doubt for the tinstone, and is at least extremely probable for the uranium, tungsten, copper,^ and iron ores. The only ores in this area, perhaps, having a different origin seem to be those of silver-lead, zinc, and some of the iron- stones. As these changes we're induced by heated vapours, they are said to be 'pneumatolytic,' and in so far as they affect the granite and the killas, since they have converted these rocks in sUu hy chemical transformations into masses of different composition, they may be said to be ' metasomatic' In this chapter the alterations in the granite, which are the most conspicuous and far reaching of all, will be considered. Where the edge of the granite, with the baked and altered killas or greenstone resting upon it, is well exposed (as at Mousehole, Tater-du, Cape Cornwall, Porthmeor, and other places) there is often a belt of fine or coarse da'rk-grey rock between the normal felspathic granite and the older masses into whichit has intruded. This rock differs from the granite in containingno felspar, but consists mainly of quartz and black tourmaline with a varying propoi-tion of other minerals, such as white mica, topaz, apatite, and usually also small quantities of tinstone. This 'schorl rock,' as it is called, has a very well-defined extetaal boundary against the killas but passes gradually and irregularlv into the unaltered granite. Hence it clearly has originated by the modification of the GRANITE. 55 granite in situ by the above mentioned pneumatolytic processes. Moreover, -vvben, as occasionally happens, the sediments have been converted into quartz-tourmaline rocks, they do not, in Cornwall at any rate, yield typical granular schorl rocks. The width of this altered margin of the granite may be only a few feet or may be twenty or thirty yards. In some exposures it is only slightly developed (west side of Trewavas Head), and in many places it is indicated by the mine burrows when the surface exposures are not sufficiently good to show it (Carbis Bay, St. Just, etc.). The schorl rock is typically granular, evenly and entiTely crystalline, and where the alteration is complete it yields little obvious trace of its derivation from the granite, especially as the large porphyritic felspars, which are so conspicuous in the parent rock, have disappeared. It is not difficult, however, to find schorl rocks in which part of the felspar is not yet destroyed, while the remainder is replaced by quartz, tour- maline, and white mica. No hard and fast line can be drawn between schorl rock and greisen, as most of the specimens from this zone contain both whit© mica and tourmaline in addition to quartz. But pure examples of both of these rocks also occur, and, as will be seen later, they tend on the whole to have different associations and a different mode of occurrence. ' Topazfels,' a mixture of quartz and topaz, so common in many Saxon tin-bearing granitea, does not occur in the Land's End area. The derivation of schorl rock from granite by gradual replacement of the original minerals is excellently shown by certain specimens obtainable on the mine tips near Carbis Bay, and at Trevalgan. In these the matrix is a dark-grey schorl rock, consisting of black tourmaline and quartz in about equal proportions. Some of the specimens contain large crystals of white or creamy felspar, similar to those of the granite. They may be a couple of inches in length, and even under the microscope are fresh and unattacked. In other specimens their place is taken by granular aggregates of quartz with a little tourmaline, apatite, and white mica. Clearly, the tock was once a porphyritic granite, in no way different from the typical coarse porphyritic granite of the Land's End mass. Under the influence of the solvent vapours the matrix, being finer-gained and more or less porous, was the first to give way. Its felspar and black mica were removed, tourmaline and quartz being deposited in place of them, and schorl rock was in this way produced. The larger felspars, being more compact and hence less readily penetrated, resisted till a later stage, but finally also were destroyed, and a mosaic of quartz and other minerals replaced them. These pseudomorphs after felspar recall the well-known pseudomorphs in quartz and tinstone after the same mineral folmerly obtained at St. Agnes and in other localities in Cornwall. Specimens illustrating the same process may also be obtained at Cape Cornwall. A variety of schorl rock long familiar to geologists who interest themselves in the Toicj-oscopic ^trticture of rocks is 5^ GEOLOGY OF LANd's END. luxullianite. It has become celebrated from its beauty as an ornftmental stone, and, the sarcophagus of. the Duke of Welling- ton is composed of it. Originally obtained in scattered blocks in the neighbourhood of Luxulyan, it is by no means common, and no large supplies of it are available. A microscopic study of luxuUianite was made by Professor Bonney.* Its special features are the presence of large crystals of red felspar in a dark matrix of schorl rock. This corresponds to one of the stages of alteration above described. Under the microscope the matrix consists of quartz and tourmaline, the latter mineral partly in compact grains of brown colour and probably original, and partly in radiating tapering needles of bluish tints spreading outwards through the quartz, and often im- planted on the surfaces of the brown primary tourmaline grains. Schorl rocks with this structure, and indistinguish- able from the matrix of luxuUianite, are found at Providence Mine (Carbis Bay), Mill Bay (Land's End), and at the East Levant Mine. The intense blue colour, strong dichroism, and pronounced zonal structure of the tourmaline in these rocks make them very beautiful microscopic objects. In microscopic section the quartz of the schorl rock forms small irregular grains, very full of small dust-like fluid cavi- ties, with mobile bubbles, exactly like those in the quartz of the granite. The tourmaline shows an extraordinary range of colours. Yellow, changing to brown when the polariser, is rotated, and blue are the commonest, but green is also fre- quent, and' violet, grey, and colourless varieties also occur. Zpnal structure is practically universal. It may be said that, as a rule, the central and older parts of the crystals are brown, the margins being various shades of blue, or sometimes nearly colourless. Only obscure traces of crystalline outlines are exhibited, usually by the cross sections of the crystals, but most of the grains are quite irregular. In addition to occa- sional crystals .of undestroyed felspar, and to a more or less constant amount of white mica, the commonest accessory minerals of the schorl rock are topaz (in irregular grains), cassiterite (rather rare), apatite (often in large crystals), zircon, and chlorite. Only ike zircon and tinstone are idiomorphic. In the microscopic sections, as in the hand specimens, it is rare to find any of the structures of the original granite preserved. Wo pseudomorphs after felspar can be recognised except where the alteration is incomplete. Probably, as Mr. Scrivener has argued, t part of the btown tourmaline replaces biotite. Some of it, however, is really primary. The blue and colourless tourmalines are, as he holds, in the main of later and secondary origin, but this cannot be established as a universal rule, for blue tourmaline and bi-own tourmaline often succeed one another in the zones of a single crystal. The typical specimens of schorl rock seem to have been entirely reconstructed under the operation of the vapours which * Min.Mag., 1877, p. 215. i Qicart.Jmirn. Qeol. Sip., voL lix., 19Q3, p. l^2< GRANITE. 57 passed outw.ards thjougk, them from tlie subjacent granite. The similatity of the rock to the purely aqueous deposit of the tin veins (so, far as regards its mineral composition) indi- cates that all its ingredients were capable of entering into solution under the conditions which prevailed. A, second mode of pneumatolytic alteration of the granite is the formation of greisen, in which the felspar of the original rock is replaced by quartz and white mica. The greisen bands exposed on the shore of St. Michael's Mount have long been famous, but are only the best known examples of a process which has been very general in Cornwall. At Tater-du, Mouse- hole, Ca,pe Cornwall, and in many places where mining has been carried on near the contact of the granite with the killas, greisen bands are frequently met with, and, like the tour- malinisation, they are not confined to the granite, but afEect also the killas and the elvans, though to a less degree. While the schorl rock is typically developed in a narrow peri- pheral belt of the granite, though it also frequently makes its appearance in veins, the greisen is essentially a vein formation in Cornwall, and is not known to occur in broad masses or in sporadic patches, whether at the edge of the granite or in other parts of it. It is, however, usually marginal, and all the best localities for it are near the actual contacts, or in places pre- sumably near the contacts between granite and country rock. In such situations vertical fissures belonging to one system of the master joints, which originated by the contraction ensuing on consolidation and cooling of the granite, are lined with greisen on each side to a distance which varies from a few inches up to a foot or more. Hence it is clear that the alteration took place at a time when the granite had solidified and cracks had formed in its mass, and the disposition of the greisen along the walls of the fissures indicates that the agent which occa- sioned its formation came up through these cracks in the gaseous or liquid condition. As we pass outwatds from the joint cracks into the unaltered granite, a succession of stages of diminishing alteration can generally be made out. The central fissure may be open, and is then sometimes lined with small crystals of quartz and mica, occasionally also with cassiterite or topaz; and as the greisen has often small pores and crevices the same minerals may occur covering their surfaces. At other times the fissure is coated with a deposit of quartz, with little or no white mica. Next follows a pure greisen, consisting of quartz, mica, often a little topaz and tourmaline, apatite, zircon, and less commonly small brown crystals of tinstone. Except the zircon and the tinstone, all these minerals occur in grains with quite irregular form. The quartz is full of fluid cavities; the mica is in irregular plates, about a quarter of an inch across; the tour- maline resembles that of the schorl rock; topaz is very com- monly though not constantly present; and the grains of apatite are abundant and of comparatively large size. In these greisens, as in the schorl rock, the structure of the granite is efEaced. It is n.ot possible to point to any definite pseudo- 58 GEOLOGY OP land's END. morplig after felspar. The whole rock has suffered recrystalli- sation. Further away from the fissure the greisen merges gradually into the granite. Felspar begins to appear often as small residues of original crystals, the outer parts of wh.ich liave been converted into aggregates of quartz and wnite mica. Pseudomorphs of this nature after felspar grains which have been completely altered may also be recognised. At first the mica is in small crystals embedded in the quartz. When the alteration is more complete the mica plates become larger, and at the same time less numerous and less intimately mixed with the quartz. There is not much evidence to show whether the tourmalini- sation preceded, accompanied or followed the greisening. Both were subsequent to consolidation, and were completed probably before the interior parts of the great granite masses had com- pletely crystallized, and while the external granite zones in which they occur were still warm, A comparison of all the evidence available, however, makes it likely that the forma- tion of schorl work is the earlier and the greisening the later, as it is certainly the more local of the two phenomena. In the former process the presence of boron compounds was essential, while the latter is mainly due to fluoric vapours alone. The third kind of pneumatolytic alteration shown by the Cornish granites is kaolinisation. While the formation of schorl rock and greisen usually takes place near the margins of the granite bosses, kaolinisation, on the whole, is most fre- quent near their centres. It does not occur in belts or along fissures, like the alterations above considered, but chiefly along vertical columns or pipes which have a more or less circular outcrop on the surface. It has been pointed out that each main granite mass in this district has a kaolinised area somewhere near its centre.* The granite is converted into an aggregate of kaolin, musGovite, and quartz, which, when coherent and still containing some undecomposed felspar, is known as china stone, but when completely altered becomes a friable mass, easily broken down by strong currents of water. The structure of the granite is preserved, and the original quartz grains and plates of mica are still visible, while the felspar is represented by soft white aggregates of kaolin, mixed with a little quartz. This method of decomposition has undoubtedly originated from heated corrosive vapours ascending from below through cer- tain broken or fissured parts of the granite. As bands of schorl rock are often clearly visible in the china-clay pits, the kaolin formation is later than part, at least, of the toutmalinisation. Possibly, however, the two processes may have been in some measure concurrent. On the whole, it is likely that the kaolinisation began at a lower temperature than the formation of schorl rock and greisen. Steam, car- bonic acid, and fluorine were probably the vapoxirs principally concerned in the process. Tinstone is occasionally found in * Keid, in ' Summary of Progress of the Geological Survey tor 1901,' p. 26. GRANITE. 59 tte kaolin works, but ttis is so Tinusual that tlie association is probably accidental. I. II. III. IV. V. SiOa 70-17 69-64 74-54 71-15 69-42 TiOa -41 — — -16 tr. AlaOs 15-07 17-35 14-86 19-41 15-65 FeaOa -88 1-04 2-63 1-32 1-25 FeO 1-79 1-97 -23 -09 330 MnO -12 tr. tr. -09 -39 OaO 1-13 1-40 -29 -21 -63 MgO 1-11 -21 tr. -45 1-02 KaO 5-73 4-08 3-73 1-44 4-06 NaaO 2-69 3-51 3-49 -05 -27 LiaO -11 tr. tr. -03 -81 HaO(105°C) ... -18 \ .„„ .„„ / -16 -06 HaO (above 305° C.) -70 j '"^ **' \ 5-09 -54 ■PaOe -34 tr. — -07 -40 01 -06 — — tr. tr. F -15 — — -11 3-36 S -04 _ _ _ _ BaOg strong trace — — -33 -59 100-68 99-92 100-54 100-16 101-75 Less O for F and 01 -07 -04 1-41 100-61 100-12 100-34 I. — Lamorna Granite. Anal. Dr. W. Pollard. II. — Gready Granite. Anal. J. A. Phillips {Quart. Journ. Geol. Soc, vol. xxxvi., 1880, p. 8). III. — Botallack Granite. Anal. J, A. Phillips {Ibid., vol. xxxi., 1875, p. 330). IV.— Kaolinised Granite, Georgia Works. Anal. Dr. W. Pollard. V. — Greisen' (with tourmaline and topaz), St. Michael's Mount. Anal. Dr. W. Pollard. A consideration of the chemical analyses given above throws a good deal of light on the composition of the rocks described in this chapter, and on the changes induced by pneumatolytic action on the granite. The small amount of lime, compared with the soda, in the first three analyses explains why the orthoclase felspat is a perthite veined with soda felspar, or albite, and shows also that albite oligoclase must be common in the rock, while plagioclases more basic than oligoclase are entirely absent. The magnesia and iron oxides, along with the lithia and most of the fluorine, belong to the micas of the rock, and to the tourmaline when that is present. Their total amount is small, as the Cornish granites are typically pale- coloured, and contain only small quantities of the dark sili- cates lithionite and tourmaline. In the kaolinised granite (Anal. TV.) the felspar has disappeared ; hence the potash and soda are greatly reduced in quantity, and what remains belongs to the white mica, which is separated from the china-clay by washing. At the same time there is a decrease in the iron oxides and magnesia, while the amount of water contained rises, owing to the abundant kaolin being a silicate which contains the elements of water. The alumina seems to be more abundant, but this is only apparent, as this substance is the most insoluble of all which enter into the composition of the granite. 60 GEOLOGY or LAND S END. If it be regarded as constant, it is probable that tbere has been a slight loss of all the other components, including the silica. There is no evidence sufficient to show that any element has been introduced into the rock and even the fluorine has dimini- shed, owing to the decomposition of the brown mica in which it is partly present. The kaolinised granite, in fact, approxi- mates very closely to a mixture of quartz (SiOj) and kaolin (2 H^O, AI2O3, 2 SiOjj), with a little muscovit© (KgO, 2 H^O, 3 Alfis, 6 SiO,). The last analysis, that of the greisen of St. Michael's Mount, shows also a diminution in the alkalies, especially the soda, owing to the replacement of felspar by quartz and muscovite. There is an increase of fluorine which must be contained in the new white mica and the topaz. It is interesting to note that the phosphoric acid (of the apatite) has not diminished but may have slightly increased. Otherwise there is little difference between the unaltered granite and the greisen, and it is some- what curious to observe how a very complete mineral trans- formation may be accomplished with very little modification in the bulk composition of the rock. In the course of the survey certain specimens of granitic and other rocks were sent to the Hon. R. J. Strutt, who was engaged in an enquiry into the distribution of radium in the earth's crust. His general result is that the average radium content of sedimentary deposits does not differ appreciably from that of igneous rocks. Among the igneous rocks " granites, as a rule, contain most radium, basic rocks the least." The West Cornwall specimens examined were: — Density. 2-62 2-62 2-61 2-99 2-60 Granite, Lamorna Quarry „ Bosemorran, St. Just „ Knill's Monument ... Greenstone, Carriole Du, St. Ives Serpentine, Lizard Silicified gritty slate, St. Ives A further observation on Cornish granite showed that " more than half of the radium is contained in the heavy minerals, though these are only | of the whole mass of the rock." The radium apparently chiefly resides in the brown mica.* Radium per gramme, in grammes. 9-35 X iO-ia 8-43 X 10-1^ 6-90 X 10-12 1-14 X 10-" 1-00 X 10-12 2-50 X 10-" Badium per c.c, in grammes. 24-5 X 10-" 22-1 X 10-" 18-0 X 10" 3-41 X 10-" 2-60 X 10-" Free. Moyal Soe., A., vol. 77, 1906, p. 472-485 ; vol. 78, 1906, pp. 150-153 61 CHAPTEIl V. ELVANS. Th.6 igneous rocks known in Cornwall as ' elvans ' are long narrow dykes of quartz-porpkyry or felsite, of slightly later date than the granite masses. It is unfortunate that the miners use the term somewhat vaguely, often including masses of greenstone and other hard rock under the term ' elvan ' ; for this makes it impossible to accept the mine plans as sufficient evidence of the occurrence of such dykes, where there is now no surface evidence, though we may be sure that many more dykes exist than have been laid down on the map. The elvans, though not differing greatly from the granite in composition, behave quite differently from granite veins. Instead of forming irregular tongues radiating from the granite masses, they form narrow parallel-walled dykes, which tend to arrange themselves tangentially to the granite bosses, but are seldom seen to cut the granite itself. In direction, they conform to some extent to the strike of the pre-existing folds and cleavage ; but they seem to pay no attention to the jointing, most of which is of later date. In shorty the elvans appear to fill shrinkage cracks formed during the cooling of the granite; but they have no direct connection with the granite masses now seen at the surface, though their partial distribution suggests that they may be confined to the area under which a granitic floor may exist at no great depth. The mode of origin of thesp fissures probably explains the behaviour of the dykes ; they commenced as narrow fissures at considerable depths, where the only lines of weakness were those of folding and cleavage, and extended gradually upwards, though it is doubtful whether any of them reached the surface. Even now, when the surface has been so greatly lowered by denudation, many of the dykes cannot be traced continuously, and dykes proved in mines cannot be found at the surface. The small extent of the metamorphism caused by the elvans, usually only extending a few inches on either side of the dyke, tells against the idea that the fissures can have acted as ducts for the flow of any large body of molten rock. The dyke seems merely to have been injected, and then the rock consolidated. There is one striking peculiarity which is found in nearly all the dykes, though apparently it is least noticeable in those that show the most granitic character — the border of the dyke on either side shows strongly-marked fluxion structure; but this chilled margin contains comparatively few porphyritic crystals, though scattered examples may occur, and the centre of the dyke may be full of them. If the crack gradually opened below and extended upwards, the first injection would be through a narrow fissure and into a comparatively cool rock. This might mechanically strain out the already formed large crystals, and cause marked banded structure in the pasty mass. 62 GEOLOGY OF LAND's END- As the fissure widened tliere would be a freer flow, through, a hotter channel; so that we might expect to find more porphy- ritic crystals, less sign of fluxion, and the rock would finally consolidate with a more coarsely crystallin© matrix. As a general rule, the less porphyritic are the el vans the greater is their fluxion structure ; though this rule is not without excep- tion, and certain wide elvans are almost non-porphyritic, and without much sign of flow. Nearly all the elvans can be distinguished from any granite mass or vein by one peculiar characteristic — the elvans usually contain numerous perfect doubly-terminated pyramids of quarta, while the quaftz in the granite is interstitial, not in isolated crystals. This character is a useful one for dis- tinguishing between the nearly contemporaneous veins of fine- grained granite and true elvans, where both cut the granite, and for recognising much-decayed elvans, for the decayed rock or soil still shows these characteristic crystals. The distribution of the elvans is very partial ; they seem in this area to be almost confined to the anticlinal ridge which ends westward near Penzance and Madron, and as the sides of this ridge converge, they converge also. The dykes rise freely through the argillaceous slates of the Mylor series ; but they seldom appear either in the sandy strata of the Portscatho series or in the masses of granite. It is not clear whether this distribution is due to the greater shrinkage of the argillaceous deposits during heating and cooling, or to their more perfect cleavage; for either of these peculiarities would tend to limit the dykes to the area within which they are now almost con- fined. The most convenient way to study the elvans will be to take them in geographical order, commencing at the west with the anomalous dyke at Sennen. This elvan seems to cut across the granite area from Whitesand Bay to Perth Curnow, run- ning from north-west to south-east — a direction taken by no other elvan in this district. It must be pointed out, however, that this direction is probably nearly parallel to the strike of the sedimentary rocks immediately to the west, off the coast ; nowhere else, except for a short distance near Newlyn, do we find such a strike. This elvan probably ■ reaches the coast under the sand-dunes of Escall's Green; but there it is entirely hidden, though the valley in which the sand has accumulated may owe its origin to the presence of this rotten dyke. Close to the high road, and near the second milestone, there is a large quarry, worked for road metal, which shows an excellent section of the dyke and its junction with the coarse porphyritic granite. The dyke is an exceptionally wide one, measuring at least 150 feet; it is a much altered fine-grained pink or white rock, now looking like a close-grained sandstone, full of radiating rosettes of schorl needles. It seems originally to have been a fairly fine-grained quartz-porphyry, with only scattered porphyritic crystals of orthoclase, these latter being now almost obliterated, though the doubly-terminated crystals nf quartz remain unaltered. EL VANS. 63 Near Poliigga there is another quarry in a similar white rock, and on the coast just east of Porth Cumow it appears in the clifE. These three exposures cannot be connected up by evidence in the field; but there seems little doubt that they all belong to the same dyke. In the parish of Sancreed, well within the granite border, commences an exceptionally long and straight elvan, the western course of which has been carefully traced, for it supplies water for the town of Penzance. From information supplied by Mr. Latham, the borough surveyor, this dyke appears close to Sellan (at any rate, it has been traced no further west). It then runs in a north-easterly direction for a mile or so, with a thickness of about 30 feet, without now showing any surface indication. Near the Penzance Water Works it has been proved at various points, and at Hea Moor it is seen in the road, and again in a quarry where it is worked for road metal. Then it is again lost, and the rest of its course can only be taken from the old map, which shows it as con- tinuing as far as Tregassack, in the parish of Ludgvan. No trace of this elvan can be found in the sides of the valleys near Ludgvan ; but after a gap of one and a-half miles, an elvan of similar character appears along the same line close to Tregellast, though it cannot be proved to belong to the same dyke. This elvan, which is a quartz-felspar-porphyry, with numerous crystals of orthoclase, has been worked at CoUurian, and also in several quarries at Canon's Town; but the stone is somewhat decayed. It is seen as a narrow dyke in the railway cutting west of St. Erth Station, and fragments occur in the mine tips further east, but it is doubtful whether it there reaches the surface. The next elvan to be described is that met with on the fore- shore opposite Penzance and Wherry Town, though no con- tinuation of it can be found in the greenstone or granite near Newlyn. This is the well-known ' Wherry elvan,' noted for its submarine mine and for its local impregnation with tin- oxide. The singular mine which was here worked will be referred to in a later chapter; it is sufficient here to say that, where worked, the elvan was 18 feet wide, and it dipped north- westward at an angle of about 60° or 70°. Near Chimney Rock the dyke seems to be three or four times this width ; but beyond the South Pier it runs out to sea, and no trace of it could be found near the Cressars. The Wherry elvan is a quartz-felspar-porphyry of the common type, showing fluxion structure and chilling at the margin ; it is much cut up by joints which, according to Dr. Boase, are continuous into the slate.* Another small elvan is traceable for about 100 yards on the west side of Penzance Harbour; but it also seems to die out eastward, for it cannot be found on the bare rocky foreshore east of the harbour. A very conspicuous and wide fine-grained porphyritic elvan forms the Eyeman and Long Bock, where it seems to have a * ' Ti^eatise on Prlmarjr Geology,' 1834, p. 62< 64 GEOLOGY OF LANDS END. widtk of about 100 feet. It is probably continuoxis at th« surface for a long distance, for afteir dis.appearing under Marazion Marshes it is again found in Newtown Brick Works, where its decomposed upper surface has been dug. According to Henwood, three different elvans were probably met with in Wheal Darlington, which mine was worked underneath Marazion Marshes. After passing Newton, we can trace the Long Rock elvan past Ludgvan Lease, Crowlas, and Rosevidney to St. Erth, north of which place it can be seen in a quarry worked for road metal. Near Tolroy it makes a curious bend, as though to avoid the tough greenstone, and from thence to Wheal Alfred it has been traced by Mr. Dixon as a non-porphyfitic dyke of moderate width. The second and third of the elvans re- corded by Henwood as occurring in Wheal Darlington not im- probably represent the two which are found in Wheal Gwallon and Wheal Virgin, for these tend to converge under Marazion Marshes. Both these elvans are worked in quarries near Wheal Virgin (south-west of Gwallon on the one-inch map). The northern elvan is noted by Mr. Wilkinson as a very hard rock with pink porphyritic felspar, the southern as fine- grained, lienwood's account of these elvans, as seen in the mines, suggests that they are extremely variable; but his statement that in certain places they shade off into slate is probably due to the great difficulty in studying junctions in a mine, where light is bad and the rocks are everywhere smeared with ochre and clay. At the surface there is never any diffi- culty in tracing a sharp line between an unweathered elvan and the slates into which it has been intl'uded. The inland course of the Marazion and St. Hilary group of elvans need not be followed in detail; they pass through the middle of a mining district, and the old mine plans and mine tips seem to indicate that a good many more branches were met with than can now be mapped with any certainty. Many details will be found in Kenwood's monograph. On returning to the coast at Marazion, we find no trace of elvan near St. Michael's Mount, though the foreshore is bare. About a mile east of Marazion, however, on the shore at Venton, there is a small elvan, which, according to Mr. Wilkinson, is seen to split up and throw out tongues in all directions and to invade both the greenstone and the slate. It is a fine-grained compact tock with distinct crystals of felspar. Another small elvan, 40 feet wide, reaches the coast at Trevean Cove, in Perranuthnoe. It is probably the same as that noted in mine plans as occurring at Trevean and Perran Downs, and perhaps again at Retallack, but may not always reach the surface. The last dyke to be met with along the south coast within this area occurs at the west end of Prah Sands. This elvan has the exceptional trend of west-north-west ; and like the nearly parallel elvan which passes through St. Hilary, is remarkable for the abundant pinite crystals which it contains. The ELVANS. 65 dyke seen on the foreshore at Prah Sands is 60 feet across ; it has a fine-grained chilled margin about 14 inches wide, show- ing marked fluxion structure ; its interior is coarsely porphy- ritic, with felspar crystals up to two inches long, and quartz and pinite crystals of about a quarter of an inch. Mr. Wilkin- son notes the tendency of the majority of the large felspar- crystals here to arrange themselves more or less parallel to the walls of the dyke. According to Henwood, this dyke dips north-eastward at 45° or 50°. It is said by the miners to be continuous to Goldsithney; but it cannot be traced at the surface, though it is certainly shown in some of the mine plans. The elvans of the West of Cornwall are mostly cream- coloured, pink, or yellow quartz-porphyries (granite por- phyries), but are sometimes brown or green from the abun- dance of limonite, chlorite, and other secondary products. They almost always contain small rounded blebs of slightly corroded quartz, and many are strikingly porphyritic from the abundance of felspars up to an inch or more in diameter, grains of quartz, and, more rarely, hexagonal plates of black mica. Others are fine-grained and carry few phenocrysts, but there seems to be no geological significance attached to these varia- tions, as the same dyke may vary considerably in these respects in difEerent parts of its course. Some dykes have very fine, non^ porphyritic margins, which seem to be chilled edges, and may be several inches across (Prah elvan) ; others are almost free from phenocrysts throughout their breadth. The groundmass is usually very fine-grained, with a felsitic or stony character, but in some dykes, it is coarser and consists of small crystals about gV*'^ of an inch across. It never, however, resembles very closely even the finer-grained varieties of the granite. The phenocrysts of felspar have the same general appearance as those of the granite, being flattened parallel to the clino- pinakoid, and having faces roughened by the persistence of growth during the crystallisation of the groundmass. They are usually Carlsbad twinned. When they are sufficiently fresh to yield characteristic microscopic reactions, they prove to be partly perthitic orthoclase and partly acid varieties of soda- lime felspar belonging to oligoclase or oligoclase albite. For the most part, however, they are much altered and may be semi-opaque. The quartz is often idiomorphic, showing the prism faces terminated by pyramids, but not uncommonly is somewhat rounded by corrosion. Black mica fbiotite) appears as large crystals in many dykes, but is generally con- verted into chlorite and rutile. When fresh it shows strong pleochroism (pale-yellow to dark-brown), and good pseudo- hexagonal form. Primary tourmaline is not uncommon in these dykes and must be a very early mineral, as it may be enclosed in porphyritic quartz or felspar. It is idiomorphic, in prisms with nine-sided or twelve-sided cross sections, and obtusely-pointed ends. Its colour is brown of various shades arranged in concentric zones, but bluish crystals (doubtfully secondary), may sometimes be seen embedded in felspar 9564 1' 66 GEOLOGY OF LAND's END. Topaz has not been seen in any of the unaltered elvans; tin- stone occurs rarely in small brown primary prisms. Finite after cordierite is very frequent (e.g. in the elvan dyke at Prah). It has the same form as in the granite, viz. : a pseudo- hexagonal prism terminated by basal planes, and under the microscope can be resolved into an irregular aggregate of chlorite and muscovite. The leaflets of chlorite yield grey or yellow polarisation colours, and their double refraction is often unusually high for this mineral. Very frequently they are grouped in radiating order in a matrix of chlorite and fine scaly muscovite, which possesses no definite arrangement. Small zircons can always be found in the sections. Apatite also is exceedingly common. The groundmass in most cases is a micro-granitic mosaic of alkali felspar and quartz, varying in coarseness, but essentially uniform in its structure. Patches of micro-pegmatite are not rare, and a feature of special interest which may be often observed is the occurrence of narrow micrographic fringes around the porphyritic quartz and felspar. These may be Jjjth millimetre up to half a millimetre in diameter, and are sur- rounded by a microgranitic matrix which possesses no graphic structure. Phenocrysts of coarse or fine micro-pegmatite may also occasionally be noted in the slides. More rarely these elvans have a micro-pegmatite base, coarse-gi-ained or very fine, and spherulitic, so that the rocks become granophyres. The same dyke may be a granophyre in some places and a granite porphyry in others. The micropoikilitic type of groundmass probably occurs, but is not common, as it has not been noted in any of the Land's End elvans. The elvans are very generally decomposed, but in addition to this, they have often experienced the same pneumatolytic changes as have been above described in the granite. All stages of the formation of greisen may be studied in these dykes, and in some districts {e.g. near the north-east corner of the sheet) this alteration is nearly universal. In this case, also, the matrix is first attacked and becomes converted into a mixture of quartz and muscovite, which is coarse or fine according to the grain of the original rock, and often preserves relics of graphic structure when the elvan was originally a granophyre. Often the greisening is local, and has been accompanied by the intro- duction of ores of tin, so that when lodes are worked in the elvans they generally contain little of the primary felspar, but much secondary muscovite. The large porphyritic felspars (as in luxullianite) are the last to yield, and they remain intact when the matrix has all passed into fine-grained greisen. The large quartzes are also persistent, and their presence serves to distinguish between the greisens formed from elvan and those formed from granite. In some of these rocks the new mica is in exceedingly minute particles scattered through very small grains of quartz; in others, it forms lal-ger flakes fre- quently bunched together in fan-like aggi-egates or imperfect rosettes. Abundance of fine muscovite in the groundmass of an elvar^ is probably a certain indication of pneumatolytic EL VANS. 67 action, as muscovite is very rarely a primary ingredient of these rocks. Tourmalinisation occurs also in the elvans, accompanied by the formation of chlorite and by the deposition of tinstone. Examples of this may be seen in the Herland Mine, where an elvan occtirs which has been changed into a dark-green aggre- gate of quartz, tourmaline, and chlorite, with some muscovite and tinstone. The tourmaline may be brown or green, and is sometimes blue. Clusters of tourmaline and chlorite, forming pseudomorphs after biotite or pinite, are common in these rocks. Very frequently the change is partial, and veins of tourma- linised elvan or sporadic patches of quartz and schorl occur in rocks which elsewhere have not been so completely modified. No instance of typical kaolinisation has yet been reported in an elvan of this district. &56i 68 CHAPTER VI. TERTIAET. EOCENK. Between the slaty rocks already described and the next geological formation represented within the area with which we are dealing, there is an enormous gap. Not only are all the Upper Palaeozoic and Secondary formations missing, but even the presence of the next division, the Eocene, is only suggested by obscure and doubtful traces. It has long been known that certain Cornish beaches yield much flinty and cherty material derived from Cretaceous deposits, such as are no longer to be found within the county ; but until the new survey was made, no clue was obtained as to the source of this gravel.* An excellent description of one of the deposits was given as long ago as 1758, by Williani Borlase, who writes as follows : — " It has been generally held by Naturalists that we have no flints native in Cornwall, but this is a mistake. Betwixt the towns of Penzance and Marazion there is a beach of pebbles two miles and three quarters long, among which many hundred flints may be picked up every day ; and lest it should be insinuated that these flints may possibly bo foreign, and brought in ballast by ships, I must observe, that in the low-lands of the parish of Ludgvan, scarce a musket-shot from the said beach, in a place called the Vorlas, there is a stratuvi of clay about three feet under the grass : the clay is about four feet deep. In this clay, immersed from one to four feet deep (sometimes deeper) flints are discovered in great numbers, their size from the bigness of a man's fist to that of a bean, their coat nearly of the colour of the clay (as in chalk we find their exteriour infected with the chalk-bed in which they lie) and their inward part died with the same colour more than half way ; the other part, near the middle, a common, corneous, brown flint. In the same bed of clay, I find sea-pebbles of opake white quartz, and some shingle; sufl3cient and evident vestiges of the universal deluge. I find also many small blue killas stones, with all their angles on ... . The flints of this bed of clay are brown within, but on the beach we have a remarkable variety, and one now before me of an opake white, is of as fine texture, and as high a polish, as any Carnelion I have ever seen " [probably the chalcedonio Greensand-chert of Haldon].+ The gravel is still dug at the place that Borlase names; it occurs, as Borlase pointed out, away from the sea and above the sea-level (usually 20 or 30 feet above), therefore it cannot be accounted for by any transportation as ballast. Though the name ' the Vorlas ' is now forgotten, the old gravel-pits will be found on the landward side of Marazion marsh. In the small pits now open the flints are subangular, often up to 2 or n pounds in weight, and are mixed with Greensand-chert and a considerable amount of the local Palteozoic material, in a matrix of sandy loam. *-,'^h^ following account is condensed from a paper by C. Reid, 'On the pvobiWft Occurrence of the Eocene Outlier off the Cornish Coast.' Quart. Jnurn. ffeol. Soc, vol. Ix., 1904, p. 113. t ' Natural History of Cornwall,' folio, 1758, p. 106. TERTIAllY. 69 lU 5ib e =Q o 55 o B u §^ Cb ft? ^ times ^vitli i ; it the Certain striking charac- teristics of these flints seem not to have attracted the attention that they deserve. Though so far from any exposure of Cretaceous rock, they are subangular; and they are weathered and ' annealed ' in the same curious way that is seen in the flints of the Eocene gravels of Devon and Dorset. In fact, the resemblance of the material to that of Haldon is so striking, that it suggests that both flint and chert are derived, not directly from Cretaceous rocks, but through the intermediary of some Eocene river-gravel. So far as we know, there is no reason to suppose that any Eocene outlier still exists in the county ; but the curious locali- zation of an extensive deposit of angular chalk- flints at Ludgvan, and the occurrence of a mass of beach-pebbles of the same flints to the leeward at MuUion, suggest that an Eocene outlier is pre- served, or lately existed, under the sea not far from St. Michael's Mount. There is a further piece of evidence, of which the bearing was not at first seen. The valley (see Fig. 1, p. 2) which crosses Cornwall from north to south, from St. Ives Bay to Mount's Bay, almost isolates the Land's End district. This depression is partly occupied by Pliocene strata ; but it obviously did not originate in Pliocene is something older, something that does not fit in late-Tertiary denudation of Cornwall. A more 70 GEOLOGY or land's end. extended knowledge of Cornisli geology suggests tliat this Pliocene strait was onoe an Eocene river-valley, now so trun- cated at both ends that we cannot say whether it ran from south to north or from north to south. The diagrammatic section (Fig. 2) shows the relation of the Land's End mass to the test of Cornwall. It will be noticed that at about 400 feet above the sea there is a strongly-marked shelf, or plane of marine denudation, of Pliocene date, this plane bearing no fixed relation to the limits of the granite. The upper boundary of this plane is a degraded clifE, which may cut obliquely across any geological boundary. The Plio- cene shelf is a striking feature throughout West Cornwall, especially on the windward side. But the Pliocene deposits are not confined to this shelf, patches being found near St. Erth at a much lower level, near the bottom of the wide open valley, which existed before the notch was eroded in its sides. The notch is the plane of marine denudation which was formed in Pliocene times near the sea-level; the parts of the pre- existing valley below that level either remained unaltered, or tended to fill up with Pliocene sediments, outlying patches of which are still preserved. The occur'rence of an Eocene outlier at a low level opposite the southern end of the valley just described, suggests that the river flowed from north to south (more exactly from north-east to south-west); but this evidence is by no means conclusive, for we must remember that Miocene earth-movements played an important part in the Hampshire Basin, and disturbances of this character may have extended into Cornwall, quite altering the drainage. The little evidence yet available suggests that Eocene rivers radiated from the high ground of Dartmoor, flowing westward as well as eastward, and that one of these rivers turned south- ward to cut through the depression leading to Mount's Bay. Whether the Eocene gravel which seems to occur beneath the waters of Mount's Bay, is a mere isolated patch or no is not clear. It may be an outlier belonging to an extensive Tertiary basin underlying the western part of the English Channel, and comparable in importance to the Tertiary basin of Hamp- shire. Some 20 miles south-west of St. Michael's Mount lies the isolated mass of phonolite, known as the Wolf Eock, on which stands the celebrated lighthouse. This volcanic rock has been a standing enigma to the geologist ; there is nothing like it in Cornwall, the only lavas of this type in Britain being of PalEeozoic date, and occurring in Scotland. On the Con- tinent the phonolites are mainly Tertiary. It has already been suggested by more than one writer that the phono- lite of the Wolf Eock may be of Eocene date, for, unlike the Palssozoic igneous rocks of Cornwall, it is neither altered nor sheared.* The occurrence of a lava-flow or neck of this exceptional type, thus placed in the course of an Eocene valley, T,,! ^■,-f"P"''*'x,'"-Sr i',''?,'^^''™^''"P*''^^ Stnichire anil Composition of n. Phonolite from tlie Wolf Rock,' Geol Mag., 1871, p 247 ; and ' Note on fchn Phonolite from the Wolf Ropk,' md., 1874, p. 462. TERTIARY. 7 1 may perhajjs be pointed to as a confirmation of tte view that an Eocene basin may lie under the sea in the western part of the English Channel. No special description of the phonolite of the Wolf Rock is needed here, as it is well known to all students of British petrology. Its nature was first discovered by AUpott, who has given an account of its microscopic characters, supple- mented by two analyses by J. Arthur Phillips. AUport's description was amended in many respects by Professor Zirkel,* and by Dr. Teall.f The rock is of considerable interest as being the best example of a phonolite known to occur in Britain. Pliocene. The only fossiliferous deposit of Pliocene date yet found in Cornwall occurs within the ancient strait just described. Though it was only discovered in 1882, it has already a fairly extensive literature, and all we can here do is to indicate its leading characteristics, and refer to the publications in which fuller details will be found. The determination of the Pliocene age of the St. Erth clay was the last work of S. V. "Wood, jun., who died before his paper was published. The most complete lists of its fauna will be found in Mr. A. Bell's paper of 1898, and in the Paleeontographical Society's ' Monograph on the Foraminifera ' (1885). The following account of the St. Erth deposit and its stratigraphical relations is mainly condensed from the ' Pliocene Deposits of Britain,' for a more detailed survey has only tended to confirm the conclusions there arrived at. Between the village of St. Erth and the Vicarage, which lies about a quarter of a mile to the east, there are some gently sloping fields, in which pits have been opened for sand, and to obtain clay for puddling for some engineering works at Penzance. Nothing would have been known about the fossili- ferous deposit if it had not been for the economic value of the clay, which led to the deepening of the largest of the pits, so that the underlying unweathered shelly clay was reached. Everywhere the angular rubbly deposit known in the west of England as ' head ' overlaps the clay, so that without artificial sections we should not have suspected the presence of anything between the head and the Palteozoic rocks. This widespread and deep deposit of head makes it impossible to trace the exact limits of the clay, but the outcrop of slate and elvan at several points in the neighbourhood shows that the basin must be of limited extent, probably less than a quarter of a square rdile, certainly under one square mile. The pit which yields the fossils lies close to the Vicarage on the north-west side, and occupies a field sloping towards the * ' Mikroskopische Beschaffenheit der Mineralien und Gesteine,' 1873, p. 397. t J. J. H. Teall ' British Petrography,' 1888, p. 367. 72 GEOLOGY OF LAND S END. nortk-west. The beds exposed in it, as far as can be seen, dip in tbe same direction, but at a biglier angle, so tbat tbe clay thins out altogether towards the Vicarage, and it is not improbable that Ihe Vicarage buildings may rest almost directly on the solid rock. The sections constantly vary as the faces of the pit are cut back, but perhaps the complete succession given by Messrs. P. F. Kendall and E. G. Bell will best show the relations of the Fig, 3. — Section at St. Erth. (Kendall and Bell.) K '.aiaJsHs^ieiSiBiaii^ S'O 8v(liii'.4.6 i OU '- -. I ''"l*^*- J- V A '^^ x\ -L T Vegetable soil. " HeaJ." Yellow sand. " Grrowder," Yellow day. Blue clay, with fossils. Quartz pebbles. Fine quartzose sand. " Q-rowder." Elvan Dyke. deposit. This section, by permission of Prof. Kendall and the Council of the Geological Society, is here reptoduced (Fig- 3). In the adjoining pit on the south (Harvey's Pit), moulding sand has been dug, and neither clay nor fossils occur. A section measured in 1901 was as follows: — ■ Head of angular slate detritus Coarse loamy sand, with scattered stones and sball quartz pebbles Loamy moulding sand, with a few scattered quartz pebbles and seams of small stones. (Some of this sand is washed very clean) Bough washed stones (touched). Feet. 2 12 On the opposite side of the valley, and about a quarter of a mile north of Canon's Town, numerous masses of ferruginous sandstone and conglomerate seem to point to another Pliocene outlier, lying at a height of about 180 feet above the sea. The exact age of the St. Erth clay still remains somewhat TERTIiRY. 73 doubtful, for the fauna is distinctly different from anything yet discovered in Britain. No fewer than 250 species of marine mollusca have now been discovered in it, and the variety of foraminifera is almost equally great. The percentage of ex- tinct species is very large, and the Mediterranean affinities of the fauna as a whole are most striking. It has been called Newer Pliocene, Older Pliocene, and Miocene. Though in the latest published account, that by Mr. A. Bell, a Mio-pliocene age and a correlation with the Messinian of the Mediterranean basin is suggested, I am still inclined to think that the fauna is slightly ^ewer, and should be compared with that of the Lenham Beds, in Kent — which, however, are by some also referred to the Mio-pliocene period. The percentage of extinct species at St. Erth is about the same as in the Pliocene sands at Lenham, and in the Coralline Crag; but there is this marked peculiarity, that the Mediter- ranean element is in much greater force. A similar contrast, however, still distinguishes the marine fauna of West Corn- wall from that of the North Sea. Other peculiarities of the St. Erth fauna are explained when we take into account the physical conditions under which the clay was deposited — condi- tions quite unlike those holding in the North Sea. If the map and section (Figs. 1 and 2) be again referred to, it will be seen that a wide shelf or ' plane of marine denuda- tion ' occurs with its upper limit close to the 400-foot contour (more exactly at 430 feet above the sea). This shelf was the Pliocene sea-bed, and its abrupt upper limit the old cliff, while the claya of St. Erth were being deposited. The grounds for this conclusion were discussed in 1890,* and our increased knowledge has only strengthened them. It may be useful, however, to give a short summary of them ; for the markedly shoal-water character of many of the most abundant mollusca is likely to mislead, unless the physical geography of the dis- trict is clearly realised. It has already been pointed out that the clay lies in a pass or valley dividing two tracts of high land. The fossiliferous strata occur at 100 feet above the present sea-level. The land rises rapidly to the south-east, so that we find an elevation of 255 feet only 600 yards away, and it should not be for- gotten that the land was once still higher, for since Pliocene times this hill has yielded the mass of angular rubble which now covers the fossiliferous bed. If the depth at which the clay was deposited were only 15 fathoms this elevation must then have been dry land ; in fact, the shore line must have coincided with the 190-foot contour, only 400 yal'ds away. What evidence is there of this close proximity of land ? The littoral shells, such as Patella and Littorina, which everywhere occur in thousands on rocky shores between tide-marks, are entirely absent, as are 'Sci-ohwularia, Cardium edkde, and Hydrobia ulvce, which inhabit the sheltered creeks and estuaTies. The only evidence of the neighbourhood of land is * ' Pliocene Deposits of Britain." Mem. Beol. Surrey, pp. 63-67. 74 GEOLOGY OF LAND's END. the finding of a few specimens of the littoral air-breathing Melampus; the empty shells of recent species of this genus will, however, float long distances when full of air. Again, the lithological character of the clay points to deposit in fairly still water; but as this area would be exposed to the force of the Atlantic swell, though somewhat sheltered by the high lands to the west, it is difficult to conceive of such clays being laid down in a less depth than 50 fathoms, especially when we take into account the enormous force of the waves at St. Ives and Penzance, which are now as much sheltered from the prevalent wind as St. Erth could have been. • Assuming that the clays were deposited in 50 fathoms, the. total depression of this area must have amounted to about 400 feet, for the fossiliferous deposit now lies about 100 feet above the sea-level. Under such conditions the character of the district would be greatly altered. Cornwall would be trans- formed into a scattered archipelago, divided by numerous straits and channels with very uneven bottoms, exactly as we find among the Scilly Islands at the present day. On this assumption the high land close to St. Erth would become a submerged shoal, reaching the lower part of the laminarian zone, but not rising above the sea-level. Like all such rocky shoals, it would be covered with a thick growth of the sea-weeds which form the favourite haunts of the various plant-eating species such as Rissoa and Odostomia. Anyone who has collected floating sea-weeds will have noticed how- largely they assist in the transportation of these shells. Thus a deep hollow close to a forest of oarweeds must often be filled with the shells of the laminarian zone to such an extent as almost entirely to mask the true character of the fauna proper to the depres- sion. Besides this, the submarine slope was here so steep that multitudes of shells must have been washed down by the to- and-fro motion of the water and dropped into any sheltered hollow below the range of wave action. It is in this manner that we can account for the chal'acter of the fauna of the St. Erth clay; the moUusca are mainly the species thiit lived on the shoal close by, and the scarcity of truly littoral forms is due to the distance from the shore. 75 CHAPTEE VII. DRIFT. Another break in the geological record occurs between the Older Pliocene and the earliest Pleistocene of the district. What happened during this interval we do not know. West Cornwall is full of unexplained phjfsical features, and the seaward edge of the Older Pliocene shelf is everywhere rounded in a way difficult to understand, though it suggests later coast lines, newer than the 430-foot cliff, but higher and older than the notch of the Pleistocene raised beach below. Eaised Beach. The earliest Pleistocene deposit preserved is the raised beach, which occurs in every sheltered bay or nook of the coast, at heights varying from the present sea-level up to 65 feet above mean tide. In this area, unfortunately, the raised beach yields no determinable fossils, though Mr. Dixon finds that near Godrevy it consists largely of shell-sand. Else- where, the constant percolation of rain water has removed the lime, leaving only a mass of beach shingle and quartz sand, very unlike the modem shell beaches of this part of Cornwall. Though varying in minor details, the general relations of the old beach to its rocky floor and to the cliff behind are very constant. A few feet above the present sea-level the sea has cut into the Pliocene platform. Where the land is high and the rocks al-e hard the shelf thus formed is a mere notch, often only perceptible to the trained eye. But where the slope is gentle and the rocks comparatively soft the shelf widens out into a broad platform, bounded inland by a small bluff, which marks the position of the ancient cliff. The one type is illus- trated in the narrow shelf along which the road from Newlyn to Penzance is carried ; the other type is' seen in the ancient bay between Penzance and Matazion, in which the old cliff is half a mile or more inland. In the space available it will be impossible to give any full account of the raised beaches ; we can only sketch out their distribution and indicate where the most interesting sections are to be seen. For this purpose it will be most convenient to follow the coast continuously from Godrevy round the Land's End to Trewavas Head. Between Godrevy and the Strap Rocks Mr. Dixon finds an excellent series of exposures of the raised beach, resting on a shelf a few feet above the present level of high water. The deposits consist of worn beach material below and blown sand above, the junction showing thin intercalations of the two. The shingle resembles the modern beach, but contains an appre- ciable amount of chalk-flint, greenstone, and other far-trans- 76 GEOLOGY OF LAND's END. ported material, tkese stones being sometimes subangular and not rounded. The sand in places consists largely of com- minuted shells, and is there generally consolidated into sand- rock ; in other parts it is thoroughly decalcified. No recognis- able shells have yet been found ; but its antiquity may be in- ferred from the fact that south-west of Godrevy it is overlaid by head 12 feet thick, which occupies a shallow depression, and this head is itself overlaid by recent blown sand. At Magow Rocks, just north of the mouth of the Red River, the foot of the old cliff is 15 feet above high water. Close to Strap Rock the beach consists mainly of coarse sandstone, with some granite, elvan, greenstone, and spotted hornfels. Much may be hidden under Phillack Towans ; but there is no evidence that the old coast line cuts back into this bay, nor is there any trace of raised beach in the estuary of the Hayle River. Small patches of raised beach will be found at the foot of the cliff north of Carbis Bay, where they Irest on a low rocky shelf; but these need not detain us, for at St. Ives there are excellent sections. St. Ives Head, known also as the Island, is a mass of greenstone, which at th© period of the raised beach formed a true island. Now it is separated from the town by a low depression occupied by raised beach and head. On the east side of this neck, at Perth Gwidden, the low clifE shows 10 feet of head, resting on 10 feet of shingle beach; in most places, however, the beach is only represented by a few inches of shingle beneath a thick mass of head. The beach at St. Ives consists in the main of local rocks ; but it yields also pebbles of granite, hard purple sandstone, chalk-flints, and chert. West of St. Ives close search will show here and there traces of the raised beach, or of the bare rocky platform on which it once rested ; but the next noticeable section is one exposed in the cliff between Wicca Pool and Gala Rocks. Here the angular head is 40 feet thick, and underneath it lies 3 feet of shingle, mainly composed of local rocks, but yielding also chalk flints up to Ij lbs. The platform below is only two or three feet above high-water mark ; where it rises higher the head rests directly on it, without any trace of beach material between. Similar sections are found in Pendour Cove, at Porthmeor, and in Portheras Cove; at the last-mentioned place the beach rises about 10 feet above the present level of high water. From this point to Cape Cornwall only occa- sional traces of the rocky shelf are to be found ; but the beach is again seen in Priest's Cove, on the south side of Cape Corn- wall. Here it yielded a pebble of biotite-trachyte, very like the Permian volcanic rocks of Devon. At Perth Nanvan there is an exceptionally fine section, with raised beach banked against a nearly vertical granite cliff, which is thoroughly waterwom up to 40 feet above Ordnance datum. The head is 20 feet thick, and rests on 20 feet of beach, consisting of enormous boulders of granite, with much killas and greenstone neat the base. DRIFT. 77 Passing Whitesand Bay and Sennen Cove, wkicli again stow traces of the old beach, still containing chalk-flints, we meet with the same deposit in each of the little coves south of the Land's End. At St. Loy there is more shelter from the Atlantic billows and there is a cliff of drift half a mile long ; it shows: — ■ Feet. Head about 15 Raised beach 3 or 4 Eook platform, (granite) varying from 4 to 20 feet above high- water level. The rocky platform is here entirely granite, and. the only other rocks in the neighbourhood occur to the east and beyond Boscawen Point — i.e. on the leeward side. Notwithstanding this, the raised beach, though mainly granite, contains much greenstone (up to 40 lbs. in weight), and hornfels, besides a good many chalk-flints, a subangular mass of greensand-chert weighing 2 lbs., and some fragments of purple sandstone. In some parts more than half the pebbles are non-granitic. When we pass Lamorna and enter Mount's Bay, the feature made by this old shore line becomes more conspicuous and more continuous ; but the shelf is so covered by later deposits that its landward limit is not at first recognised as a buried cliff, and only occasional patches of the raised beach itself are visible. From Mousehole northward to Newlyn, as already mentioned, the road runs along this feature. Penlee Quarry exhibits one of the most important sections (see Plate IV.) of these old marine deposits to be met with in West Cornwall. The quarry has cut through the shelf and the old cliff, and in one corner, between the quarry and the road, the ancient beach is seen to rest on a rocky waterwom platform at a height of 65 feet above Ordnance datum. The beach consists of well-rounded boulders, often as large as a man's head, and is mainly of local origin ; above it is a mass of head and rainwash from the hill above. Raised beach is said to occur at a still greater height in Penzance, in Morrab Road ; but this seems to be a mistake, the height being about the same as in Penlee Quarry. North of Penzance, the old cliff line is traceable inland through Gulval to Ludgvan, and then southward to Marazion ; but this part of its course is hidden by market gardens and deep soil, so that we cannot correctly ascertain the maximum height to which it rises in a sheltered bay. From Marazion eastward, there are numerous sections of the raised beach, always at low levels, and they call for no special remark. One of the best of them, that at Prah Sands, is described below and illustrated in Fig. 4; another excellent exposure will be found close to the eastern limit of our area, in Tremearne Cliff. Head and Steeam Tin. In the foregoing section various mentions have been made of the curious deposit of angular detritus known as 'head, ' 78 GEOLOGY OF LAND's END. which overlies the raised beach. This deposit, however, is not confined to siich situations; for it fills the bottoms of all of the valleys, and spreads out into wide, gently sloping deltas or sheets wherever the valley opens out on to low ground. The material seems to have resulted from the shattering of the rocks by frost during the Grlacial epoch, and to have been distributed as we now find it by the floods caused by the melting of the snow. It occupies gentle slopes and plains in a way that no coarse gravelly deposit can do under present climatic' conditions in Cornwall. At present, however, we cannot point to any direct evidence of Arctic conditions within this area, though Arctic plants have been found in similar deposits in Devon, and in Scilly Mr. Barrow has found seams of ice-scratched erratics, driven up by pack ice, alternating with the head. This shattering by frost, among other results, must have set free large quantities of the tin-ore disseminated through the granite and altered slate. The violent floods which followed the melting of the snow were just the conditions under which the material would be washed and sorted according to specific gravity, so that the heavy tinstone would usually be found in a layer at the bottom of the gravel, as it commonly occurs. Some of the stream tin is found in more modern deposits; but its usual association is not with the modern alluvium. It will be noticed that on the map the valley deposits which yield tin have been coloured as alluvium, not as valley gravel. This was necessitated by the circumstances that the recent peaty alluvium generally covers the head, and in streaming for tin has been turned over with it, so that the two deposits are now thoroughly mixed, except where the head happens to form a terrace at a distinctly higher level. In this district almost every valley yields more or less tin, and has been systematically streamed. It is needless to describe in detail the distribution of the head ; but it may be mentioned that it is a most unsatisfactory deposit to map, except where it lies in a valley or abuts against an old cliff. Else.whe're, on the lowlands, it forms sheets with such indefinite outlines that it seems impossible to limit them, and rather than obscure the geology, some of these covering masses, such as the one hiding the Pliocene deposits of St. Erth, have purposely been omitted. Some of the best sections of the head will be seen in the cliffs of Mount's Bay, especially near Marazion, where it forms cliffs 40 feet in height. It consists everywhere of angular detritus of local origin, washed from the hills behind. Close to the hills, it is full of large angular masses of rock ; further away the stones are smaller and are more mixed with loam. The bedding is often very obscure, but always slopes away from the hill. "We will take one section as typical, and give in some detail an account of the cliff at Prah Sands; for this locality has yielded the only trace of fossils or of man yet found in the Pleistocene deposits of "West Cornwall. The following account is condensed from that given in 1904, and the illustration DRIFT. 79 reproduced fcy permission of tlie Council of tke Geological Society.* Tlie section lies between Sydney Cove (where the road comes down to the beach) and the well-known 'Prahelvan/ less than 300 yards away, and close to the western horn of the bay. The general relation of the deposits will be readily understood from the accompanying section (Fig. 4). An uneven, wave-worn, rocky platform rises to about 15 feet above high-water on the south-western side of the elvan. Beyond and behind it is a much-degraded ancient sea-clifE, with traces of caves, now well above the reach of the sea. This buried cliff trends inlandj and then strikes eastward at a distance of about 200 yards from the present coast. On' the rocky platform and banked against the clifi rest patches of shingly beach (mainly of elvan and killas), with big boulders and much sand, the whole deposit seldom reaching 10 feet in thickness; the beach-material has been entirely decalcified, and is now cemented by iron into a solid mass. About 60 feet of angular rubble or ' head,' loamy at the bottom and full of large blocks of elvan throughout, at this point rests upon the raised beach, forming the modern sea-clifE. On the east side of the elvan-dyke the rocky platform gradually sinks to mean-tide level on the foreshore; and at 70 yards from the elvan it is lost under recent beach, or has sunk beneath .the sea ; it has also a slight seaward tilt. The strata to which, we wish particularly to draw attention are those now visible at the foot of the cliff, where they rest upon the ancient marine deposits, and are clearly seen to pass under a great thickness of ' head.' Perhaps the clearest way to show their relation is to give detailed measurements at a point where the cliff is nearly vertical and free from talus, and where the recent beach opposite has been swept away, so as to lay bare part of the foreshore. Such a section, was measured at about 150 yards east of the elvan : — Thickness in feet. Soil 3 ' Head ' or coarse angular rubble of local rocks (elvan, slate, and some greenstone) ... ... ... ... ... 20 Loamy "head," mainly consisting of vein-quartz 12 Black loam, with fragments of charcoal, burnt bone, and burnt earth 0^ Grey sandy loam, with small stones and traces of roots throughout 8 Clean grey sand (marine) 1 Ferruginous gravelly beach OJ At this point the rocky platform could not be reached, the lowest bed seen only lying a foot or two below high-water mark. It will be noticed that in the section just described, the marine beds are succeeded by a few feet of sandy loam or brickearth. This loam is traceable for about 200 yards, and is * C. and E. M. Reid, ' A Probable PalEeolithic Floor at Prah Sands. Quart. Jov/rn. Geol. Soc, vol. Ix., 1904, p. 106. 80 GEOLOGY OP LAND S END. t3 I °5 m II m I — I .S ,3 II 13 CO II seen wherever tlie foot of tke cliff is free from talus. In part it may be only worked-up material formed from the marine strata below; but, in the main, it seems to be an ordinary soil washed from the slopes above, for it is full of small chips of vein- quartz, though larger stones are uncommon. Towards the ancient buried cliff which for- merly bounded the old bay on the west, the loam becomes more stony and like the ■ head ' above, but un- fortunately that part of the section was somewhat obscured by landslips, and we could not ascertain exactly where the change occurs. Careful examination shows that the loam was at one time a true land-surface, for it is full of small vertical roots. Uirfortunately, these are preserved only as ochreous casts, too much decayed for microscopic examina- tion. Towards the top of the loam occurs a black seam, usually about 6 inches thick. At first this was thought to be peaty; but on washing a quan- tity of the material, we could find no trace of seeds or other determin- able fossils. We found, however, that the black colour was due to abundance of small fragments of char- n ,. . „ , . coal, mixed with small splinters of carbonized bone, and fragments of burnt earth. On further examination, we ascertained that this char- coal was particularly abundant at several spots where the loam, Fft' :, II M ^ II 1^ /rS c3 O w.a '-<>. DBIFT. 81 aa a rule nearly clean, contained groups of three or four blocks of flattish. slabs of stone, wbicb were generally of elvan. At these spots the black loam was commonly full of pieces of quartz, usually small, possibly the remains of larger blocks shattered by fire. As we had evidently found a true land-surface, on which man had made hearths and lighted fires, a careful search was made in this black layer. Unfortunately, the deposit seems to have been thoroughly decalcified and the fossils destroyed by percolating water, for only carbonized remains are preserved. We found, however, that some of the larger pieces of vein- quartz in this layer were apparently fashioned into rude imple- ments ; but these had been battered into shape, not flaked. Above the black seam just described come several feet of loamy drift, in which the etones consist almost entirely of vein- quartz. Such a material is at the present day the ordinary soil of the country, where time has allowed of the decay of all other rocks. Under present climatic conditions similar material is being washed down the slopes, to accumulate in the flat-bottomed valleys, such as this must have been. The quartzose loam passes upward into the well-known ' head ' or rubble-drift of Cornwall, which consists of an obscurely stratified mass of local rocks, in blocks of all sizes, included in a more or less loamy matrix. This deposit is so porous that any fossils have disappeared, if such existed, and we are still without direct evidence as to the climatic con- ditions under which it was formed; but the evidence seems decidedly in favour of the generally accepted view, that it belongs to the later stages of the Glacial period. Its mode of occurrence strongly suggests soil-cap movement, or movement aided by snow-slopes or masses of half-melted snow. The blocks which it contains are fresher, larger, and have travelled farther down gentle slopes, than is possible under present-day conditions. It differs from the modem rainwash and soil, and from that below in which the supposed implements are found; but these two land-surfaces so closely resemble one another, that it is not easy to distinguish them where landslips have brought the two into juxtaposition. Alluvium and Submekged Fobest. After the formation of the head came a period when the land stood at a higher level above the sea, so that the seaward ends of the river valleys were cleared out and deepened. In these valley bottoms, now below the sea-level, grew the vegetation which forms the ' submerged forests ' of the coast ; for when the sea again rose the trees and marshes were overwhelmed, and alluvial or estuarine silt, often of considerable thickness, was deposited on them. At the bottom of this alluvium, as we should expect, a certain amount of stream tin is also to be found.* •An extensive literature relating to these deposits will be found in the early volumes of Tram. R'y. 9eol. Soc. Cornwall, especially in the papers by Boase and CarnPi (See Appendix II.) 9664 '^ 82 GEOLOGY OF LAND's END. The principal exposures of this submerged forest and of the accompanying alluvium are to be found in Mount's Bay, between teuzance and Marazion ; but if we could examine the deposits beneath the modern beach we should find similar remains opposite the mouths of the larger streamSj such as the Hayle River and Red River. Near Penzance, the submerged forest takes the form of a peaty soil or carbonaceous clay, resting on an uneven rock-surface at various levels down to and below extreme low water. The clay is full of vegetable matter and drifted logs of oak ; it also contains numerous roots and stumps of hazel, and in places of oak. Notwithstanding its low level, it yields no marine fossils, though it contains elytra of beetles and numerous seeds. The best places to examine this submerged forest seem to be opposite "Western Green and opposite Chyandour, though it must also be nearly continuous as far as Marazion. Near the Wherry Rocks we found in this deposit seeds belonging to Rammculus Flammvla Linn.^ Rubus frutioosus Linn., PotentUld, Ajuga reptans Linn., Qiiereus Robur Linn., Corylus Avellana Linn., Carex. It is very difficult to examine deposits beneath the sea-level ; but this particular sheet of alluvium was cut through at Huel Darlington, on Marazion Marsh, and an excellent account of it was preserved by Carne,* whose description is here quoted : — " A stratum of alluvial tin-ore having been discovered in Huel Darlington Mine, several fathoms below the surface, a pit has been sunk at a short dis- tance east of that mine and near Marazion River, in order to discover the tin there The first eight feet consist of slime, gravel, and loose ground (the slime having probably been conveyed there by the frequent overflowing of the river) : the next four feet consist of a bed of peat, rather soft, full of minute woody fibres, and when dried, fit for fuel : below this is a bed of white sand, twelve feet in depth, containing a large quantity of cardium edule : under the sand there is a layer of trees, prin- cipally oak and hazel, all prostrate, and lying in all directions ; the largest (oak) being about fourteen inches in diameter and thirty feet in length ; hazel nuts are very plentiful, both loose and on the branches of the trees : they contain no meat, but are full of water. One piece of oak, about fourteen feet long, appears to have been wrought, as if it had been intended for the keel of a boat : the trees occupy only from one to two feet in depth, as there is rarely more than one in thickness : the crevices between them are filled with sand from above : these trees rest on a bed of hard solid peat, three feet thick, of closer texture than the upper bed, and very fit for burning : then we find four feet of alluvial tin ground, the stones or pebbles in which are rarely larger than a hand ball, — generally much smaller, and rounded at the edges : this stratum rests on the clay-slate rock." As the height of the ground at this spot is only about 12 feet above mean-tide level, and the deposits penetrated are 31 feet thick, it is evident that both .the rocky floor and the lower peat must be beneath the level of the lowest spring tides. Dujsrrs, Extensive dunes of blown sand, or ' towans ' as they are liero called, fill the deeper parts of St. Ives Bay, and smaller areas of dune occur in Mount's Bay and in Whitesand Bay. * Trans. Roy. Qeol. Soo. Corn, vol., vi , 1846. p. 233, DRIFT. 83 This sand is noticeable for its great mobility, for it consists mainly of small flakes of sliell, which easily rise and skim through the air. By far the largest area of sand-dune is that known in different parts as Lelant, Phillack, or Upton Towans, though it is a continuous sheet, broken only by the estuary of the 1-Iayle River. The greater part of these dunes is now fixed by vegetation, and accretion only takes place at the seaward face. Now and then, however, the dune bursts its bounds, and, advancing, overwhelms the good land, behind. It has over- whelmed the small chapel of St. Gothians, and sand is banked high round the churchyard walls at Phillack ; but at present the chief area of fluctuating dune is the barren tract at the mouth of the Red River, where ' desert ' conditions can be well studied. The narrow dunes known as Eastern and Western Greens at Penzance were formerly much larger; but for the last century they have wasted rapidly. Were it not for the addi- tional protection afforded by the railway, the sea would now break into Marazion Marsh. The exact reason for this alter- nate accumulation and removal of dunes is not easy to ascer- tain. It may be connected with periodic variations in the climate ; but quite as probably it is due to some more obscure cause. If some insect plague, for instance, were to attack the wild thyme for a season or two, the destruction of this plant, which is one of the main constituents in the turf that binds the dune, might lead to an overwhelming advance of the sand, which it would take years of vegetable growth to master. Loss OF Land. • Though so exposed to the sweep of the Atlantic billows, this hard rocky coast changes but slowly, though the once-con- tinuous shelf of the raised beach is becoming less and less conspicuous. The only district where coast changes are rapid and important is the low land at the bottom of Mount's Bay, between Penzance and Marazion. Here, there is nothing to resist the waves except a narrow band of beach and sand-dune ; and the sea would encroach steadily were it not for 'the presence of the railway embankment. The loss of land has been so conspicuous near Marazion that it seems curious that in recording it geologists have not more generally observed its bearing on the supposed early date of the isolation of St. Michael's Mount. If the encroachment of the sea has gone on for 1900 years at the rate recorded by early writers, it is obvious that when Diodorus Siculus wrote the Mount must have deserved its Cornish name, supposed to signify " the hoar rock in the wood," for the swampy wood of Marazion Marsh must then have extended seaward and sur- rounded the Mount. In that case, the description given about 90 B.C. of the island of Ictis, from which the tin was shipped, could not possibly refer to St. Michael's Mount.* Cam© * See Reid, ' The Island of Ictis,' Arvhaologia, vol. lix,, 1905, p. 281. at V O 5^ 84 GEOLOGY OF LAND's END. carries back the traditional name to tke period of the lower peat-bed, or ' submerged forest ' ; but we have no evidence of any change of the relative level of land and sea at so recent a date as 90 B.C., and we now know that these submerged forests belong to the Neolithic period, probably at least 3,000 years ago. It is most improbable that Cornish was then spoken here, or that any traditional name would last for more than 2,OO0 years after the Mount had become an island. A few hundred years back, however, would probably see the Mount connected with the mainland, and deserving its traditional name. 85 OHAPTEE VIII. ECONOMIC GEOLOGY. Ore Deposits. Though this was formerly an important mining district, and was probably a mining district as far back as the Eronze Age, the mines are now to a great extent worked out and abandoned. At the time of writing, all alluvial working for stream tin has ceased, and a few tin and copper mines are all that are in operation. Perhaps the present high price for tin may encourage the re-working of certain of the mines for the neglected poorer ores, and in a few places trials are being mad© for the rarer metals, such as silver and uranium; but great numbers of the miners have already emigrated or have turned to other occupations. Tin and copper mining in Cornwall has been carried on mainly near the margin of the granite, where that rock is in contact with altered slate or greenstone. The distribution of the ores is, however, extremely partial, for the margin for long distances yields nothing of value, whilst other parts are exceptionally rich. So irregular is the distribution of the lodes, as laid down on the map, that at first sight it does not seem necessarily to indicate any close connection with the granite intrusions, for many of the lodes are far distant from any granite mass seen at the surface. When, however, we take into account the contour of the buried granite masses and their proximity to the surface, as suggested by the extent of the metamorphism, and also the probable nearness in certain places of the slaty dome which once covered what is now bare granite, the close relation of the lodes to the intrusion of the granite becomes more evident. Though they are obviously connected with the intrusion of the granite, the valuable ores are concentrated into certain limited and well-defined areas, the fest of the margin yielding but little. Thus we find a rich group of tin and copper lodes in the parish of St. Just, and another smaller but very valuable group near St. Ives, both these being close to the northern margin of the Land's End granite. The intermediate area, howevet, yields nothing of value, except for a group of tin- lodes at the Ding Dong Mine, which occupies an unusual position in the heart of the granite mass. The rest of the granitic area has yielded little^ though there must be a con- siderable amount of tin, in the form of strings or disseminated grains, for all the valleys have yielded stream tin. From Penzance eastward through St. Hilaiy, and north- eastward through St. Erth and Eosewarne to Camborne, there is a wide mining area, north and south of which come districts yielding little. This mining region extends for some distance 86 GEOLOGT or land's end. outside the belt of metamorpkism whicli has been mapped; but it is included in the more extended region which shows the influence of the granite in a less marked degree. The rich mines seem to be in some way connected with the anticlinal structure already referred to.. It is curious to note also that, in a general way, the elvans converge and disappear towards Tenzance, and that both lodes and eivans have a similar dis- tribution — where the elvans converge and disappear westward the lodes disappear also. The connection of elvans and lodes, however, is not a necessary one, for neither the St. Just nor the 8t. Ives mining district shows any elvans at all. The coincidence of lodes and elvans in certain areas is most probably due to their both occupying fissures formed by the intrusion and cooling of a ridge of granite connecting the Land's End mass with the bosses further east. The cooling of such a buried mass would necessarily produce fissures parallel to itself. The earliest formed of these fissures would ibe injected with molten rock, while the later, formed when the granite had crystallised, contains ores deposited by hot gases or solutions. It is noticeable that the cracks into which granite veins are injected seem never to contain metallic ores, nor do the fissures continuing elvan dykes. Ores are found in fissures formed after the granite had solidified, and after cracks could remain open to great depths in the still-hot mass. In order the better to illustrate the distribution of the ores, Mr. MacAlister has drawn up tables showing the amounts obtained. The figures are approximate, for only partial statistics are available. He has also compiled statistics of the yield of the different mines, and has added descriptions of each mine for which this information is available. This additional information is given in Appendix I. (p. 93). It may be useful here briefly to describe four or five mines which may be taken as typical of the mode of occurrence of the ores and of the method of winning them in this district. We will select the Levant Mine (see pp. 108-112) as showing the relation of the tin and copper lodes to the margin of the granite, and the method of working beneath the sea. St. Ives Consols shows another type — the carbona or irregular mass of tin ore. Wheal Trenwith is noticeable for its peculiar mixture of copper ore and pitchblende. The Wherry Mine was worked in an elvan dyke impregnated with tinstone. In the Perran silver mine we see a lode of exceptional character, of unusual trend, and probably of much later date. Before describing these modern mines, it may be well to point out that much of the working in this area is of extremely ancient and unknown date. 'We find shallow trenches and mines worked by the ' old men,' of which all record has been lost. In most cases, however, later trials or workings on the same lode have so obliterated the earlier workings that the archaeology of the mining is most difficult to unravel. There is as yet no clear dated evidence of mine working in this area in Roman or earlier times; though, considering the con- ECONOMIC GEOLOGY. 87 spicuousness of tlie copper stains and the easy accessibility of the lodes in the clifl, it is difficxilt to imagine that such work- ing did not take place. St. Ives Consols. — This mine lies immediately west of St. Ives, and is in granite near its junction with the slate and greenstone. The principal lode runs along the valley bottom. The peculiarity of the mine consists in its enormous irregular pockets or masses of tin ore, which, branching off from some of the lodes, swell out so that in their working caverns were formed upwards of 50 feet in height and width. These pockets, or ' carbonas,' as they are locally called,* contained an •enormous quantity of tinstone mixed with tourmaline, and yielded black tin to the value of about £500,000. The masses of ore seem to represent altered granite, and are more allied to the masses of schorl rock described on p. 55 than to true veins. The lodes at St. Ives Consols appear to have been merely narrow ducts up which the ore-bearing vapours travelled; but occasionally their influence spread irregularly in an exceptional degree into the surrounding rock. The mass of schorl rock at Trevalgan was also worked for tin, but was of little value. Wheal Trenwith and Providence Mine. — These mines were worked, pal-tly under the sea, between St. Ives and Carbis Bay. Their main lodes are approximately parallel to those of St. Ives Consols, but yielded mainly copper. They were richest in tin when in the granite, and in copper when in slate and greenstone outside the granite. Both mines were remarkable for the occurrence of pitchblende in considerable quantities mixed with the copper ore. In fact, the amount of this ' impurity ' in the ores was so great at Wheal Trenwith, as Henwood records,! that " cores were . . . inspected, and pitchblende being discovered among them, its nature and prejudice to the copper ores were explained to the workmen, by whom it has been, of course, since rejected." Now, of course, pitchblende is far more valuable than the copper ore, and the mine tips are being turned over for the rejected material, whilst preparations are being made for re-working the abandoned mine. Wherry Mime. — An elvan dyke is visible at low tide on the foreshore opposite Penzance, between the Battery Wharf and the Wherry Eocks. Part of this dyke, opposite Wherry Town, is so impregnated with granular cassiterite and permeated by thin strings of black tin as to make it a valuable ore. It was first worked in a small way about the beginning of the 18th century.J About 1778, a shaft was sunk on the foreshore, and later on the works were extended and connected with the land by a long wooden bridge, shown in Hawkins' plate. The * Robert Hunt derives this word from carbona a treasure-house, and quotes St. Matthew in the Rheinis version, "Non licet eos niittere in carlonam." This is the exact sense of the word to the Cornish miner. t Op.-oit, p. 19, and Table xvii. j Hawkins, 'On Submarine Mines.' Trant. Jioy. Gcol. Soo. Cm-n., vol. i., 1818, p. 127, and Plate I. SB GEOLOGY OP land's Eijt). elvan was worked for its full width, of 18 feet, and was found to underlie 1|^ feet in a fathom towards the north-west. Ore to the amount of at least £70,000 was obtained, but the mine was then destroyed by a vessel which, drifted from its anchorage and demolished the stage and machinery. Perron Silver Mine. — Near Perranuthnoe there are numerous tin and copper lodes, having a trend of about west- north-west, or about the same general direction as the elvans. One mine, however, on a lode trending north-north-west, is so peculiar as to deserve mention, especially as it was being worked and was examined during the recent survey. We have to thank Mr. G. D. McGrigor for further particulars. The' lode distinctly cuts the tin and copper lode of Wheal Neptune, and seems to be of later date ; but this point is not quite clear, for though the lode contains iron and silver ore, it yields also occasional masses of tinstone. It may be a spur from the main tin lode, re-opened and filled with new minerals at a later date. Trial was first made for the iron ore. This turned out to be of little value, but some small greenish crystals were noticed, and these were found to be silver chloride. When the ferruginous ' gossan ' was more closely examined it proved to be a very rich silver ore, though not occurring in large masses. One parcel of 20 cwts. of the picked ore yielded 841 ozs. of silver. In places, a little argentiferous galena has been found, but the common ore is the silver chloride. This lode is a good example of a ' caunter,' or lode running in a different direction from the usual one of the district. Such lodes often yield nothing but quartz or veinstone; but if they contain ores, the ores are not uncommonly quite unlike those of the main lodes. Silver is not confined to this lode, for a sample of tin-stone from Wheal Verrant yielded at the rate of nearly TOG oz. per ton. Miners speak also of numerous cross-courses and slides which traverse the country and more or less dislocate the mining ground. The cross-courses are usually quartz reefs of later date than the lodes and contain no ore; but sometimes they yield ore, as in the Perran silver mine just described, and then they would often be called lodes. The slides are simil_ar fissures filled with loose earthy material; they are usually faults. The most important of the cross-courses is the one which, running south-south-east from Gwinear to Breage, shifts the whole of the lodes — though its exact effect and the amount of its throw are difficult to ascertain, for, according to the mine plans, its effects are very uncertain. A wide earthy cross-course or djrke is said to run from Penzance into the heart of the granite; but we cannot find that it causes any dislocation. The mine plans show numerous cross-courses and slides; but none of them shift the geological boundaries in such a way that we can prove the magnrtude of the dislocation. It maj be pointed out also that in many cases a miner's ' fault ' or ' slide ' is merely a pre-existing fissure along which the lode has run for a certain distance. This will account for the ECONOMIC GEOLOGY. 89 extraordinary way in wMch. the same cross-cours© sometimes seems to faiUt two adjacent lodes in opposite directions. China-Clat. The kaolinised centres of the granite masses in this area have yielded a considerable amount of china-clay; but this industry for the present is concentrated mainly in the St. Austell district, though the clay will again be worked at some future time. The amount of prepared china-clay shipped from Penzance and Porthleven in 1904 amounted only to 6,571 tons. Moulding-Sand. Sand suitable for moulding has long been dug in the St. Erth pit (Harvey's). It occurs in strata of Pliocene date. Sand for building purposes is scarce and not very good ; it is largely obtained from the weathered inland edge of the sand- dunes, where the sea-salt, and sometimes the lime, have been removed by the percolating rain. Building Stone. Building stones of fair quality are so abundant that there is no need to carry them far. For local purposes, a good stone can usually be obtained within a mile or two, and granite, elvan, and the baked killas are all used. The greenstone comes out in irregular masses and is too tough for working. The principal stone of the district is the well-known Land's End granite, which has been extensively quarried at Lamorna, Sheffield, Carfury, and New Mil], near Penzance, and at Zennor, besides smaller quarries in softer rock. The stone is a very coarse-grained grey granite with large felspar crystals. These felspar crystals often lie with their longer axes in one direction, and in that case greatly facilitate the splitting of the rock by means of wedges into long thin blocks. Often there axe two sets of joints at right angles, sometimes even three; where the crystals are arranged in one direction there is commonly a system of joints parallel to it. In the Lamorna quarries the crystals interlock and lie in all directions. This adds to the strength of the stone, though it renders quarrying more difficult. In most of the other quarries the stone is readily split into gate-posts, or even into beams, which are often used to span wide doorways or to support the roofs of sheds. This stone is commonly employed for dressing, even where the main part of the building is built of tine-grained granite, elvan, or killas. Much of the Land's End granite is sent away by sea; but it is at a great disadvantage, owing to the absence of convenient and safe harbours. The margin of the granite close to Penzance and St. Ives does not yield a good stone. The good stone is nearer the interiol- of the mass, and it has to be carted to Penzance and St. Ives for shipment. The fine-grained granite of Gulval Downs and Castle-an- Dinas is much used- in Penzance, and is often known as ' elvan,' ' freestone,' or even as ' sandsiwne.' The part quarried 90 GEOLOGY OF LANd's END. is only the upper 15 feet, in which the rock is a bufE freestone, much warmer in colour than the coarse granite. It will not split in the same way as the coarser material, and it is notice- able that the local gate-posts are never made of it, but are brought from a distance. The bottom of the quarries shows a greyer and much tougher rock, which at present has been very little used. Though extensively used in Penzance, the fine- grained granite does not appear to have been exported. It would probably be obtainable in larger blocks at a greater depth. Throughout the killas area the elvans have been extensively vised for building, and it is noticeable that the engine-houses of most of the abandoned mines are built of elvan rather than of killas. The elvans are commonly freestones, only obtainable in blocks of moderate size, for these dykes are much and irregularly jointed. The stone varies greatly, from a whitish or bufE material resembling a fine sandstone, to a coarse purple igneous rock, or true porphyry, with large scattered crystals of orthoclase and pinite. No quarry is worked on a latge scale. Near Newlyn there is a group of quarries in which the Mylor slate has been baked and hardened by the granite intrusion; but it still retains its parallel bedding, and it can be readily quarried in flatfish blocks. Away from the granite the Mylor slate is too soft and too easily affected by the weather to make a good building-stone, though it is commonly used in cottages, and for banks. The Portscatho beds yield a hard sandstone, occurring in thin beds ; this is used at Hayle. Road Metal. A considerable business has lately grown up in the export of road metal from Newlyn and St. Ives to London and other distant places. The rock worked is an extremely tough green- stone baked by the intrusion of the granite. There are three large quarries — Gwavas, Penlee, and Penolva — between Newlyn and Paul, and another at Carrack Dhu, near St. Ives. Samples of the road metal have been deposited in the Museum at Jermyn Street. For local purposes a variety of rocks are used, for the altered greeu stone is expensive to break. Over the granitic area, schorl-rock or hornfels is commonly ©niployed, old mine-tips or stream workings being ransacked for the harder lumps. Elvan is also employed and is a good deal better than granite ; but the different elvans vary a good deal. The highly altered elvan of Sennen is carted for a considerable distance. In the killas area the old mine tips are extensively used as a source of road metal; but this material, though cheap, is very uneven in quality and does not make a good surface. The best surface for light traffic is made by the decayed granite, which tends to set into a firm smooth crust, excellent for cycling, but break- ing up, under heavy traffic. The greenstones away from the metamorphic aureole are too much sheared to be of much value, except in the harder cores of the larger sheets. economic geology. 91 Ornamental Stones. Little use has yet been made of the ornamental stones of the district, though there are several handsome varieties. The ordinary type of granite, however, is a cold grey and is seldom polished ; where it is of a warmer tint the felspar is commonly decayed. Among the altered granites there is a great variety of colour and grain; but as a rule, only blocks of moderate size are obtainable. Some of the varieties of schorl-rock are handsome black and white stones, and ought to polish well ; for instance, there is the rock of Trevalgan, with large white or pinkish felspars, or pseudomorphs of quartz after felspar, in a dark-grey matrix of schorl rock. Or there is the granular whitish rock near Knill's Monument, in which occur large scattered radiating nests of schorl needles. In the waste heaps of Providence Mine, at Carbis Bay, a great variety of these altered granites will be found, including large masses of greisen, or quartz rock, full of sparkling white mica and some schorl ; ordinary schorl rock ; and a variety identical with the ' luxullianite ' of the Lusulyan district. Among the elvans, that of Prah Sands would probably polish well, forming a purplish porphyry of coarse grain. Most of the other elvans are probably too fine-grained ; but the much- altered pink and white mottled elvan of the Land's End, with its scattered rosettes of black schorl, might make a handsome stone, resembling that found near Knill's Monument. The altered greenstones are very hard and tough, and are commonly of a fairly uniform dark-green colour. But some of the brecciated greenstones, or greenstones with pale streaks and lenticles in a dark-green matrix, ought to polish well, liocks of this character are found in the quarries near Chyan- dour and in the cliffs of St. Just; the wet beach pebbles at Penzance will often show the appearance of the polished stone. Specimens of all these stones have been placed in the Museum of Practical Geology. Water Supply. Notwithstanding a heavy rainfall, the water supply of the district is not always satisfactory. This is partly due to the jointed nature of the granite, which allows the. water rapidly to sink out of reach ; partly to the imperviousness of the slates, which at once shed the water; and partly to the numerous abandoned mines, which not only drain the country more rapidly than would occur under natural conditions, but often yield water too charged with minerals to be of any value as a source of supply. The supply of good water might, however, be greatly improved. Penzance obtains its supply from a disused mine-adit on Lanyon Moor, and from open trenches in that neigjxbourhood. These works in winter give 350,000 gallons per day; but in summer the surface supply fails, and the total shrinks to 100,000 gallons. A new deep well in an elvan close to the 92 GEOLOGY OF LAND's END. reservoir can supply 215,000 gallons per day (12 hours' pumping), and this amount can be largely increased by pump- ing longer. St. Ives is supplied mainly from old mine-adits in the neighbourhood, St. Ives Consols, Eosewall Hill, Trenwith, Trelyon Consols, and Wheal Mary all being used. The supply is never less than 170,000 gallons per day, and can be largely supplemented by pumping from the West Virgin shaft in St. Ives Consols.* * The p.irticulars are mainlv condensed from Dr. J. Spencer Low's Kepojt to the Local Goveinnient Board, 1904. (No. 200.) 93 APPENDIX I.— MINING. By D. a. MacAlistee, A.E.S.M. DiSTKIBXITION OF THE PeINCIPAL MiNEEAL AeEAS. If the principal mines and mineral centres be considered iu relation to the granite they are seen to be situated about its margin, or in the altered killas beyond (Fig. 5). The richest mineral districts ai^e frequently, although not neces- sarily, associated with numerous elvan dykes, while both in bearing and in underlie the lodes and elvans are often similar. The area may be divided into two parts. The western por- tion is made up principally of the Land's End granite mass; and the eastern portion consists of killas and greenstone, with the exception of the Godolphin granite boss. The most important mineral centre for tin and copper ores has undoubtedly been the group of mines near St. Just, and particularly those situated on the clifEs north of St. Just, where the workings extend below the sea. Of this group the most notable is Levant Mine, which is the only one raising ore to any extent at the present time. Botallack Mine, which has Recently been restarted, is the next of importance, and, counting the various smaller mine setts of which it is composed (Wheal Cock, Camyorth, and the Crowns Mine), has yielded nearly as much tin ore as Levant, and a large amount of copper. The St. Just mineral area comprises the district from Pendeen on the north to the Gribba Point, south of Cape Cornwall, and from the coast inland for a distance of from two to three miles. The mining region west and south of St. Ives, like that of St. Just, is situated near or at the granite margin. Some of its mines have yielded immense quantities of tin ore, but, unlike those of the St. Just region, they have been compara- tively poor in copper, and the mines are more scattered. The St. Ives district includes the mines west of St. Ives (St. Ives Consols, Eosewall Hill, etc.), and the mines round Knill's Monument, Trencrom, and Canon's Town. In the eastern portion of the map, in the killas area, is the Gwinear mining district, and south of it the mining district of Gwinear Downs ; both of these yielded tin and copper ores, but mainly coppel-. South of these districts is the mineral area having the Godolphin ^anite boss as its centre. On the eastern side of the mass is the celebrated Wheal Vor and Wheal Metal dis- trict, which lies between the Godolphin and Cammenellis granites, and has been described in the Camborne Mining Memoir. On the north of the Godolphin granite are a few mines such as Wheal Osborne, and others. On the west is an old and extensively worked mining region having St. Hilary, P4 GEOLOGS OF LANDS EKD. Perranuthnoe, and Kenneggy as important centres, and ex- tending westwards to Marazion. Within the granite area are several mines, the most important of whicli is the Great Work. There are a few mines near Penzance, hut none are now working. Finally, in the middle of the Land's End granite mass, in Fig. 6. — Sketch map showing the distribution of the Tin and Copper Ores, the parish of Madron, is the old Ding Dong tin mine, quite cut off from other mineral centres. North of Ding Dong, on the sea coast, is a group of small mines which includes Cam Q-alver, and Morvah and Zennor United. These mines have teen worked for tin, MINING 95 iS^ATUEE OF THE LoDES AND (JrE BODIES. In a later section, giving accounts of individual mines, des- criptions will be found of some of the bodies of tin ore wbicb, owing to their richness or remarkable form, have attracted the attention of early writers. Many of the mines were closed down about the year 1875, owing to the large foreign supplies of tin ore, and until lately there has been no encouragement to restart them. Although the prospects of a revival in the Cornish tin mining industry are great, it will be some time before any real opportunity will be afforded for actually inspecting the mines, so that dependence must be placed on old published information. As far as is known, all the ores are connected with joints or fissures of some sort, and the variety of forms the bodies of ore may assume is mainly dependent on the nature or form of the Assuring. Thus, in St. Just much of the ore is con- fined to narrow fissures, in the working of which the stopes and drivages are, in consequence, so narrow that two men cannot conveniently work abreast, and single-handed drill- ing is chiefly employed in breaking ground. Some of the richest of the St. Just mines {e.g. Levant) are working lodes of this kind. Whether these lodes are formed along simple joints, or whether along lines of fracture accompanied by dislocation of the walls, is not always clear, but probably both modes of formation are represented. Although many of the smaller fissures in Balleswidden Mine are cracJss with no apparent dislocation of the walls, some of them contain mineralised breccias, indi- cating either crushing together of the walls during actual dislocation, or comminution by violent earth tremors at the time the lodes were formed. In either case the walls of the lode have sometimes shifted since the lode was formed, and this has been accompanied by fresh depositions of minerals. There appears to have been dislocation accompanying the formation of some of the lodes in Botallack, Levant, Provi- dence, Wheal Trannack, Herland, Duffield, and other mines, as is indicated by the occurrence of granite, elvan, etc., in one wall of tbe lode; which is not seen in the corresponding position in the opposite wall. As in many cases, how- ever, the lodes are formed at the junctions of dissimilar rocks, the evidence of the faulting by lodes since they were mineralised is not conclusive. In the Gwinear district, and lu the region to the south, some of the lodes consist of wide breccias or crush-conglomerates cemented by tinstone and copper ores. The breccias and conglomerates consist of angular or rounded fragments of the country rock, which may be killas, greenstone, granite, or elvan. Such occurrences probably indicate that the lode was a plane of dislocation. At Gwinear Consols the lode in the eastern part of the mine consists of conglomerate with angular fragments of slate and rounded pieces of elvan, some of which are 30 or 40 lbs. in weight, and in one place, near a granite vein, rounded pieces of granite 96 GEOLOGT OF LAND's END, v were found in the vicinity of a cross-course,* In West E.ose- warne Mine, at a depth of 74 fathoms from surface, boulders of granite of various dimensions up to 6 feet were found in the lode, while a breccia and conglomerate of elvan, killas, and granite also occurred. t Breccias, cemented by copper ore, occur in Wheal Trenwith (St. Ives) ; cemented by tin and copper in Wheal Fortune (Marazion) ; by tin ore at Perran- uthnoe Downs (near St. Hilaxy); and by copper ores, blende, and carbonate of iron at Binner Downs. In New Eosewarne Mine a conglomerate containing tin ore has been recorded by Sir Clement Le Neve Foster, while round stones of granite and other rocks have also been noted as occurring in Relistian, Herland, Trevaskus, Duffield Mines, and Wheal Alfred. The discovery in the lodes of rounded fragments such as those just mentioned has led to discussion as to their origin, some writers maintaining that they 'are actual pebbles which have found their way into the lodes from the surface. This idea, in view of all the facts, cannot be supported. As another instance of the occurrence of nodular or conglomeratic fragments connected with fissuring may be mentioned that recently seen at the 278-fathom level in Levant Mine. This conglomerate, which consisted of green- stone embedded in a clayey matrix, occurred in a guide or cross-course traversing the greenstone country rock near the old submarine shaft. Among the abnormal forms of ore bodies to which attention has been directed by early writers are the carbonas, so well typified in the St. Ives Consols Mine, which will be found described in the " Notes on Individual Mines." These irregu- larly-shaped deposits are nothing more than exceptional developments of the features of ordinary lodes, and in all cases are associated with cracks or joints. They are pipe-like or irregularly-shaped bodies of tin ore, schorl, chlorite, and quartz, with other minerals, and owe their origin to great alteration and mineralisation of country rock (generally granite) in the neighbourhood of a vein. The vein with which the mass is associated is frequently at right angles to the ordinary lodes of the country, which is another characteristic feature. Carbonas occur in the Providence Mines (St. Ives), Rosewall Hill and Ransome, East Levant, as well as in St. Ives Consols. At St. Aubyn and Grylls a small pipe-like deposit, resembling a carbona, occurs in elvan. Writing in 1758, Borlase+ stated that " tin ore is also found dispersed in spots and bunches in the body of the stone where there appears no fissure, lode, floor, ot rectangular intersections as in other strata. The spots are sometimes so large and numerous when in granite (as in Trevegean in St. Just), that they well requite the labour of the tinner, though he is gener- ally obliged to blast the rock and afterwards break it with sledges in order to get the tin." This observation of Borlase * W. W. Kundell. Trans. Hoy. Geol. Soe. Corn., vol., vii. 1847, p. 37. t H. C. Salmon. Quart. Journ. Geol. fine, 1861, p. 517. t 'Natural History of Cornwall,' p. 161. MINING. 97 is no doubt largely borne out, but the statement that the ore is unconnected with fissures of any kind is incorrect, and is explainable by the. fact that quite an extensive alteration and impregnation of the country rock can take place through a small fissure. The deposits of Balnoon, formed by the intersections of veins, have been described by Hawkins and Henwood as stock- works. Where the lode has a more or less horizontal position it is called a ' floor.' According to Came, " St. Just abounds in floors of tin more than any other part of Cornwall. In the slate at Trewellard tin floors have been wrought near surface, and the deepest is only seven fathoms below it." They occur at the junction of several lodes, and are from one to two feet in thickness and 20 feet in width. Tin floors occur in the Herland Mine and in Wheals Eeeth, Speed and Vor. Examples of floors are also to be found in the so-called ' Grylls' Bunny ' in Botallack, and in Trewidden Bal, both of which are in killas. The mode of occurrence of the tin ore in Wheal Jennings furnishes another interesting form of deposit. The ore in this mine occurs in veins which run across an elvan nearly at right angles, and extend only a short distance into the country rock on either side. They vary in size from a few inches to a microscopic degree of fineness. By far the largest number of the ore deposits are found in the ordinary lodes and in the country rock in their neighbour- hood. Particularly do they occur in the parts of the lodes near the granite and killas junction. The structures which the lodes exhibit vary considerably. Some are mere cracks or part- ings, which are worked together with country rock in the immediate vicinity of them, as those in Balleswidden. Larger lodes exhibit comby structures showing successive depositions of minerals, as those in Wheal Bellan, Botallack, Binner Downs, Wheal Julia,* Godolphin.* and Wheal Strawberry. In New Eosewame Mine Sir Clement Le Neve Foster dis- tinguished six periods of lode formation by observing the order in which the minerals appeared to have been deposited: (1) quartz and tinstone, (2) arsenical pyrites, (3) chlorite, (4) pearl spar, (5) chalcedony, (6) iron and copper pyrites. When the lode is brecciated and has been subjected to several periods of infilling it may be wide and of complex structure. Where the lode contains less than a certain percentage (say 1^ per cent.) of tin ore it is not worked unless the condi- tions are very favourable to the extraction and treatment; and as the percentage varies in different parts of a lode it is only in those places where the lode is rich enough that any- thing but exploratory work will be done. These richer patches of the lodes are called 'bunches.' The way in which lodes die out in the direction of strike varies,, and it has been noted that the lodes in some cases die out gradually into the cleavage * Figured by De la Beohe. ' Geological Report,' 1839, p. 340. 9564 ^ 98 GEOLOGY OF LAHD S END. of the country, as at He'rland, Binner Downs, PoUadras Downs, etc., while in other cases they continue for great distances as mineralised fissures containing nothing of economic value. Beabing of the Lodes. The lodes of the various groups of mines have bearings which differ con- siderably in different localities. In the eastern part of the map, the Godolphin granite boss appears to have modified the strike of the killas and of the lodes in its vicinity, while in the Gwinear district there are two sets of el vans which appear to correspond to a certain extent with directions taken by some o^ the lodes. The lodes of the St. Just district take several directions. Those on the north of St. Just (Boscaswell, etc.), have a strike of W. 33 deg. N. to W. 40 deg. N. The Wheal Cock and some of the Botallack lodes strike about N. 20 deg. W., and are more or less parallel to the Old Bal lode of Levant Mine. Other lodes in Botallack, in common with those of Wheal Edward, bear N. 37 deg. W. In addition to these, there is a system with a bearing W. 7 deg. N. to W. 10 deg. N., as at Spearn Consols and in some of the Botallack lodes. The lodes of Wheal Owles and Wheal Boys strike N. 40 deg. W., but some are nearly east and west. The Pendeen lode in the north of the region has a bearing N. 7 deg. W. and almost coincides with some of the guides or cross-couises, wiich, how- ever, generally bear a few degrees east of north. In the district south of St. Just the lodes have a direction N. 40 deg. W. At Trevegean the bearing is E. 28 deg. N., at Balleswidden from W. 40 deg. N. to W. 45 deg. N. A few iron lodes and cross-courses also occur having various bearings. In the group of mines situated above the cliffs near the Brandys, east of Morvah, there are two sets of veins bearing respectively N. 20 deg. E. and N. 42 deg. W. On the cliff's north of Morvah there is an iron lode and a guide having north and south bearings. The lodes of Ding Dong Mine, ia the parish of Madron, in the heart of the granite country, run in two directions, K. 30 deg. N. and N. 30 deg. W., respectively, and intersect each other. Round Sanoreed the lodes vary from E. 28 deg. N. to E. 50 deg. N. In the eastern part of the map the lodes have a variety of bearings, and the particulars may be given as follows : — In the newer granite, near Amalebrea, the lodes of Georgia Mine vary from E. 12 deg. N. to E. 35 deg N. The lodes of South Providence, Wheal Sisters, and Wheal Merth, etc., have au average strike E. 25 deg. N. The lodes of St. Ives, Rosewall Hill, and Carbis Valley vary from E. 22 deg. N. to E. 40 deg. N. in bearing ; St. Ives Consols lodes strike E. 26 dog. N. ; Rose wall Hill and Ransome United E. 40 deg. N. ; Trelyon Consols E. 35 deg. N. ; Trelyon Downs and the Providence Mines E. 22 deg. N. On the eastern side of the Hayle River the lodes of the Boiling Well Mine and Wheal Lucy strike respectively B. 25 deg. N. and B. 30 deg. N. The lodes of Treloweth, West Alfred, Mellanear, West Alfred Consols, Wheal Alfred, and Alfred Consols strike E. 20 deg. N. and underlie N. The lodes of the Herland Mine B. 20 deg. N. to B. 30 deg. N. The lodes of Relistian, Vyvian, and North Rosewarne E. 30 deg. N. There is also in the last group of mines an east and west lode (called Copper Bottom lode) running into New Rosewarne Mine. Between Praddam and Burnt Downs, including Howe Downs, on the north, the lodes strike E.30 deg. N., but some of them have a more east and west bearing. East of Praddam, including part of Wheal Tremayne, West Wheal Treasury, Wheal Treasury, and Burnt Downs, aud the series to the MINING. 99 south, in which is West Wheal Abraham and Binner Downs, there is an east and west series of lodes. In addition to these, there are a number of Gaunter lodes with a general bearing W. 30 deg. N., e.gr. the Clowance Gaunter lode near Bosparva and the Bed lode running from Wheal Garpenter, through Lambo to Wheal Strawberry, and apparently continued in the lodes of Wheals Dumpling, Courtis, and Millett. Between the Godolphin granite mass and Marazion, which includes the district of St. Hilary and Perranuthnoe, there are several series of lodes, the directions of which appear to have sooie relation to the position of the Godolphin granite mass. The Darlington and West Wheal Darlington lodes in Marazion Marsh, strike E. 10 deg. N. but there are some striking W. 20 deg. N. From East Wheal Fortune through the north of Trevarthian Farm to Penberthy Crofts and also in the Gwallon Mine, the lodes strike a few degrees south of east. The Wheal Prosper lodes through to Trevarthian Farm strike E. 40 deg. N. From Ennys Wheal Virgin through Gurlyn and Lewis Mines to West Carzise and Truthwall and Gwinear Downs, the lodes strike E. 30 deg. N., but there are a number of lodes bearing due east and west or a few degrees N. of E. As a series the lodes of these mines are not definitely traceable except in a general way. The lodes at Kestal (Wheal Friendship) and the Guskas Mine bear E. 30 deg. S., but one in Guskas strikes E. 30 deg. N. To the south, the principal lodes of Tregurtha Downs (Wheal Hampton), Owen Vean, and Trevelyan strike E. 20 deg. S. Westwards these lodes are split up, but are represented in Wheal Rodney and Wheal Virgin by a lode striking E. 7 deg. S. The lodes of Trenow, Charlotte, and Trebaryah, as also those of Wheal Caroline, Neptune, etc., near Perranuthnoe, strike E. 30 deg. S. The lodes on the immediate west and north of the Godolphin granite have two or more directions. A lode passing through Speedwell, Wheal Speed, and St. Aubyn and Grylls Mine has a bearing E. 28 deg. N. Lodes having more or less the same bearing are found in Millpool, Wheal Florence, and Halamanning. Another series has a bearing B. 20 deg. S. to B. 40 deg. S., but some of them, as at Halamanning, have a more east and west bearing than this, and most of the mines in this district have both series of lodes represented, e.g. Wheal Georgia, Great Western, Speed- well, Speed, St. Aubyn and Grylls, Wheal Florence, Millpool, Leeds and St. Aubyn, West Godolphin, etc. On the immediate north of the granite the lodes of Wheal Osborne and tliose on the north of Godolphin Hall have a bearing north of west, but there are also some cross-lodes wth a bearing north cf east. Within the Godolphin granite the lodes of the Great Work Mine strike E. 45 deg. N., but some are B. 30 deg. N. and others E. 65 deg. N. The lodes of Wheal Vor, only the western parts of which come into this district, strike E. 25 deg. N. On the south of Wheal Vor is Wheal Metal with lodes bearing E. 35 deg. N. ; and the Carnmeal Mine lodes E. 25 deg. N. ' Ceoss-Coueses, Teawns, oe Gdides. The cross-courses, known in the St. Just district as guides and in St. Ives as trawns, are a series of fissures, joints or faults which traverse the district in a general north and south direction. With one or two excep- tions they contain no metallittirous minerals, and, like the lodes, have practically no effect on the geological structure of the region, except where here and there they appear to liave determined the directions of valleys. One of the most important of the cross-courses is that which has been traced from Alfred Consols in the parish of Gwinear to the east of Godolphin 9564 °^ 100 GEOLOGY OF LAND's END. Cross, and thence to Wheal Fortune in the parish of Breage, with a bearing of from N. 26 deg. W. to N. 30 deg. W. All the lodes it meets in its course are faulted in a right-hand direction. Many other cross-courses occur in the region comprised between the eastern margin of the map and the granite of the Land's End mass, and have more or less similar bear- ings ; and where faulting has occurred it is generally towards the right hand. In the St. Ives district the trawns have a general bearing N. 15 deg. W. The guides of St. Just have, according to Henwood, an average bearing E. 26 deg. N., but they run in various directions about true north. Some of the lodes have a direction so nearly north and south that they are called guides. The occurrence of metalliferous minerals in cross-courses is rare, but in some places silver ores and blende have been recorded. The most important association of metalliferous mineral with a cross-course was in the Herland Mine, where from the 90 to the 120-fathom level, near the- iuterseotion of the cross-course with a copper lode, about £8,000 worth of silver ore, consisting chiefly of vitreous and arsenical silver ore and black oxide of silver, was obtained.* In the western cross-course in Trevaskus Mine, blende with quartz, fluorspar, etc., are said to have been found.! Notes on Individual Mines. Alfred, Wheal.— The average width of the lodes is 2^ feet, but the Gaunter lode varies from 9 to 24 feet. This lode underlies north 2 feet per fathom, and is traceable into the Herland Mine. The following minerals have been recorded : — Melaconite or black copper ore, copper pyrites, mimetite, cerussite, malachite, chalcedony, pyromorphite, kerate, copper glance, cuprite, erubescite, fahlerz, silver ores, and fluorspar.* Ann, Whbal (Phillack). — Arsenic, chalybite, cerussite, native silver, silver glance, calamine, grey silver ore, and ores of copper. Balleswiddbn Mine. — The mine has not been worked since 1875. The information concerning it is mainly derived from a paper by Dr. Poster and Captain Rowe.§ There are three principal lodes. Awboys Lode. — Bears W. 40 deg. N. to W. 45 deg. N. and underlies S.B. from 15 deg. to 30 deg. The lode consists of a nttmber of parallel veins (called ' gries ') containing cassiterite. These gries vary in width from that of a mere joint to 4 inches, and consist of tinstone with tourmaline, quartz, kaolin, and a mica called gilbertite. Wolfram, bismuth, bismuthine, and native copper with fluor also occur. Each gry is enclosed between hard walls from 2 to 6 inches in width, known as the ' hard work,' consisting of quartz, schorl, and gilbertite, with mica, fluorspar, and some tinstone. The felspar of the granite has been replaced in this altered rock by quartz and gilbertite. Beyond each gry and its accompanying wall of hard altered granite (known as the ' hard work '), the country rock is kaolinised and is known as ' gook.' SoutJiLode.— The lode has a structure and bearing similar to that of Awboys, from which it is distant about 20 fathoms. New Lode.— Has a bearing more towards the west than the other lodes which it intersects in the northern part of the workings. It is a mass of hard work traversed by gries containing mispickel, wolfram, tin, and copper ore. * Joseph Carne. Trans. Roy. Geol. Soe. Corn., vol. i., 1818, p. 118 t W. J. Henwood. Ibid., vol. v. , ISiS. Tab. xxxv. t According to William Phillips (Trans. Seal. Soc, vol. ii., 1814), 45 000 tons of copper ore were yielded between 1801 and 1814, and sold for £35o' 000 the profit amountmg to £120,000. In 1814 1,500 hands were employed on the mine and the monthly expenditure was £5,300. Henword states that the total amount realised by sales of ore in 11 years before 1871 was £715 2'9 The working costs were £504,175. Dues, £71,523. Total, £575,698. Proflcs £1S9 531 From the adjaceat mine of Alfred Consols for 16i years before the same time £293,152 was realised. The working costs were £179,000. Dues £lfi ini Total, £195,104. Profits, .£98,048. ' "^"'i"*- § Trans. Boy. Geol. Soo. Corn., vol. x,, 1879, p. 10. MINING. 101 In addition to these there are lodes called 'Pie (odes ' composed of quartz, schorl or tourmaline, cassiterite, and gilbertite (a cellular rock known as 'pie'). One of the pie lodes strikes nearly B. and W. and underlies N. 10 deg. Intersecting the South lode it runs into Awboys lode. Another pie lode strikes S. 20 deg. E. "and is a nearly perpendicular irregularly-jointed lode. The Spar Lode is a quartz vein 12 feet in width striking W. 34 deg. N. and dipping S.W. It heaves the New lode in a left-hand direction. It contains numerous fragments of the country rock (granite). There are several cross-courses, slides, and fluccans (or clay courses). The cross-courses consist mainly of quartz and have a bearing about E. 40 deg. N. with a general north-westerly underlie. The slides are similar in bearing and underlie but contain red clay. The ' clay course ' is a cross-vein bearing N. 12 deg. W. with a westerly dip. It consists of decomposed granite for a width of 60 feet and is traversed by irregular quartz veins. The ore of the mine, including both ' hard work ' and ' gries,' yielded about 60 lbs. of black tin per ton. The adit is 16 fathoms from surface, and the deepest workings are at 162 fathoms below adit. According to Lean* the maximum amount of water discharged from the mine by pumps was 16-35 gallons per minute. The minimum was 10'46 per minute. Fig. 6 is a section of New Balles- widden Mine which is the adjacent sett on the south. NN Fig. 6. — New Ballesvndden Mine. N.E. BAiiNOON MiNB. — The occurrence of workable ore in this mine was very uncertain, and appeared mainly to depend upon the intersection of the Goath vein by numerous small veins having no regular strike, but which, when followed singly, dwindle and die out. Some of the irregular deposits have been characterised as stockworksf and some were supposed to be quite unconnected with Assures or veins of any kind. The Goath vein, according to Henwoodt has a bearing of N. 35 deg. E. and an underlie N.W. 20 deg. to 40 deg., varying in width from a few inches to over 30 feet and contain- ing schorl and tinstone. Although proved for a distance of 120 fathoms, it has not been worked below 35 fathoms from surface. As before stated, the tin ore in the Goath vein occurs principally where the lode is inter- sected by small veins. Some of the bunches of ore associated with these strings resemble small pipes or floors in the lode. North Vervis Lode. — Bears E. 30 degrees N. and has a northerly under- lie of 10 deg. to 40 deg. Varies in width from a mere parting to 30 feet, and is very irregular down to the 60-fathom level. Bell Mine (St. Erth).- from the mine. -Anglesite and pyromorphite have been recorded Bellan Minb. — Part of the St. Just United Mines. Worked extensively * iJep. Urn/. Com. Poly. Sac, 1836, p. 135. t J. Hawkins, ' Tin Floors.' Trcms.Roy. Geol.Soc. Corn., vol ii., 1822, p. 29. X Ibid., vol. v., 1843, p. 24. 102 GEOLOGY O* LANDS ENt). in the upper levels by the 'old men,' who left many open cuts. There are (according to Henwood) eight lodes traversing the sett, most of which have a bearing of from W. 40 deg. to 45 deg. N., a few having bearings from E. 30 deg. S. to B. 35 deg. N. In width the lodes vary from 4 inches to 14 feet, and are principally vertical or north-underlying. The Bellan lode is a tin-bearing lode, the central part of which is occupied by a strong vein of comby quarts with an infilling of jasper or ferruginous silica. The tin ore occurs in peach or ' keethan ' (soft clay peach), situated between the wall of the lode and the quartz vein. The country rock is a tourmaline granite. The other contents of the lodes are amethystine quartz, chlorite, specular iron ore, limonite, chalybite, and vitreous copper. The mine was re-opened in 1899 and is still working in a, small way on two lodes known as the Bellan and Widden lodes re- spectively. Both are of similar character and only 10 fathoms apart. BiNNER Downs Mine. — The lodes vary from 1 to 8 feet in width down to the 96-fathom level, and consist of quartz, iron and copper pyrites, earthy brown iron ore, black copper ore, green carbonate (Strawberry or Gooseberry lode), chlorite, celestine, cassiterite, blende, galena, etc. (South lode), copper and iron pyrites, quartz, etc. (North lode). A Cauuter lode bearing south of east, and about 4 inches in width, consisting mainly of quartz, also traverses the sett. It is common in this part of the country to have lodes bearing in directions B. 25 deg. S. to E. 25 deg. N., and the three principal lodes of this mine have bearings differing considerably from one another, the main lode being that on which Wheal Sarah, and Crenver and Abraham worked. According to Lean the amount of water discharged by the pumps when the mine was working in 1833, 1834, and 1835, was between 1,196'04 gallons per minute (maximum) and 66'09 > gallons per minute (minimum). Bolton, Wheal. — Situated on the same lode as was worked in Rospeath and Great Wheal Fortune. There are four lodes (according to Henwood) worked to different depths down to the 77-fathom level. Three of them have an almost east and west direction, and vary in width from 1 to 4 feet, consisting of quartz, chalybite, limonite, slaty clay, iron and copper pyrites, and black copper ore. There is also a Gaunter lode bearing S. 5 deg. E. varying in width from 2 feet to 2 fathoms, and consisting of slate and clay with quartz. It heaves the other lodes. BosoASWELL AND BoscASwrBLL DowNS MiNE. — Several lodes occur in this mine, among the more important of which are the Bridgework, Bill and Boscaswell Downs lodes, which have been worked to varying depths down to the 210-fathom level (adit being 28 fathoms from surface). The work- able parts of the lodes vary in width from 1 to 4 feet or more and contain quartz, earthy red iron ore, specular iron ore, tin ore, chlorite, tourmaline, some iron pyrites, and native copper. Opal was also found. A guide which traverses the mine in a direction N. 30 deg. E. contains quartz, jaspery brown and specular iron ore, and clay. The lodes have a general bearing W. 33 N. to W. 40 deg. N. BoswEDDBN AND WHEAL Cahtlb (including Wheal Call).— According to an unpublished report of Warington Smyth* in 1864 the deepest workings were at 95 fathoms below surface. In 1822 Carne stated that the workings in Wheal Castle had been carried a distance of 10 fathoms seawards from the coast. The lode varied from 4 to 7^ feet and consisted of quartz, limonite, and oxide of tin, with some pyrites, galena and blende, and pearl- spar. In the Wheal Call part, the Praze lode contained copper glance and grey ore. At the 50-fathom level this lode yielded tin ore, but the workings were not carried seaward. The positions of the principal lodes are shown on the 6-inch maps. BoTALLACK, Wheal Cock, and the Crowns Mine. — These mines are noteworthy alike for the richness of the lodes, the fact that they have been worked beneath the sea for a distance of between 500 and 600 yards, and the peculiar mode of occurrence of the workable masses of ore, as well for • In the Office of Woods and Forests. MINING 103 as tor the great variety of minerals found, Tlie mines have been referred to by Borlase (1758),* Pryoe (1778),t Hawldns (1818)4 Carne (1822),§ Henwood (1843), |j and in an unpublished reportby Warington Smyth (1857).«) The mines are traversed by a number of lodes, some of which cau be seen outcropping in the cliff. The bearings of these lodes differ somewhat, although the general trend is north-westerly. In 1882 the workings were down to a depth of about 240 fathoms below sea-level. Since the most productive parts of the lodes occur near the junction of the granite with the overlying killas and greenstone, the workings on the lodes have been carried seawards as they were deepened in a direction parallel to the dip of the granite surface. As Warington Smyth said : " The best portions of the veins have, with increasing depth, to be sought for at increasing distance from the shore ; and in the deepest levels driven from the Engine shaft at Botallack, the distance traversed in the vein before any ore was arrived at has been from 300 to 400 fathoms. The deepest levels (at 150, 165, and 180 fathoms) from surface respectively, are, without being rich, yielding a moderate quantity of copper ore, with which scarcely any tin is inter- mingled, although that metal is raised in considerable amount from the ' old mine ' under the land," At the 205-fathom level a considerable body of ore was worked out. According to Henwood, the Narrow or Crowns lode varies in width from 2 to 12 feet, but the other lodes are small. The minerals occurring in them are limonite, quartz, vitreous copper ore, oxide of tin, arsenic, antimony, amethyst, atacamite, aragonite, bismuth (in veins in jasper), bismuthinite, pharmaeosiderite, blende, black and purple copper ore, blue carbonate of copper, cobalt, cobaltite, chalybite, malachite, native copper, cuprite, diallogite, manganite, magnetite, mispickel, erythrite, fahlerz, galena, gothite, native silver (mentioned by Borlase as having been found in 1753), specular iron ore, smaltite, stannite, jasper, vivianite, and pyrrhotite. One of the remarkable modes of the occurrence of ore in Botallack Mine has been referred to by Pryoe and others, who state that in a place known as Grylls' Bunny, there were a series of ' floors ' or flat deposits of tin ore and 'cockle' (schorl rock) alternating with decomposed ochreous greenstone. These floors have also been noted as occurring in granite in the same mine. In connection with ordinary lodes. In the Crowns Mine the lode, varying in width from a few feet to 10 feet, has been explored below the 235-fathom level. In Wheal Cock, which includes the old Tolvean Mine, the lodes worked were the same as those wrought in Botallack and the Crowns Mine, with the exception of lodes having a nearly east and west direction coming in from Camyorth. In the old days the lodes were worked seaward in the shallow levels, and in some cases there was a thickness of scarcely 3 feet of rock between the workings and the floor of the sea. In one case a borehole actually tapped the sea bottom, the nearness of which, owing to the dryness of the working place, was not fully appreciated, although stones could be heard rattling on the sea bottom in stormy weather. The length of the workings under the sea is between 400 and 500 yards. Henwood mentions four lodes in Wheal Cock, all of which have yielded copper ores and some tin ore. The other noteworthy constituents were carbonate of iron, quartz, and earthy red iron ores, and a variety of compounds of copper, iron, etc. Henwood states that for a period of 40 years before 1871 the total receipts by sale of ores from Botallack amounted to £513,465. The working costs were £405,085. Lords dues, £23,602. Total, £428,687.** Brea Tin Mine (Brea Consols). — This mine is situated about li miles west of St. Ives, in the parish of Towednack. It was worked for tin ore beneath the sea to a small extent, but was abandoned after some years' trial in 1871. * ' Natural History of Cornwall, p. 206. t ' Mineralogia Comuhiensis,' p. 21 . J 'Submarine Mines,' n-ans. Roy. Oeol. Soo. Corn, vol. i., p. 130. § 'Mineral Productions of St. Just,' iUd., vol. ii., p. 290, and ' On the Veins of Cornwall,' ibid., vol. ii., p. 49. II Ihid., vol. v., p. II, and Tab. vii., viii. t I" the Office of the Woods and Forests Department. ** Address Boy. Inst. Corn., vol. iv., 1871, p. 37. 104 GEOLOGY Of LAND S END. Caenellob Mine (near Gurnard Head). — The lodes were not rich in tin ore, and the mine, which started operations in 1872, was closed down in 1876, Carntoeth. — Atacamite, botallaetite, specular iron ore, and tinstone have, among other minerals, been found in this mine. Careiok Du Mine. — Worked for tin and copper ores, but closed down in 1861. Caezisb Consolidated Minbs.^ — Traversed by two lodes having an east and west direction ; one is the South Binner Downs lode, and the other the West Wheal Abraham lode. According to Henwood the " Carzise " lode varies in width from IJ to 5 feet down to the 85-fathom level and consists of quartz, slate, cassiterite, copper pyrites, mispickel, and blende. There is also a Gaunter lode striking E. 12 deg. S. consisting of quartz, slate, copper and iron pyrites, and tin ore. Cunning, Wheal.^ — The Wheal Gunning lode is nearly vertical, the back of the lode being under the roadway behind Boswedden Place. Henwood states that it has been worked to the 90-fathom level. The workable part of the lode varies in width from 6. inches to 4 feet. The ' guide ' from Boscean and Botallack on the north also traverses this sett. The veinstuff consisted of quartz, chlorite, schorl, and tin ore. Wheal Daelington. — There are two lodes. One has a southerly under- lie and a bearing of E. 10 deg. N. Its outcrop is not far north of the Methodist Chapel at Newtown. The other lode, with a bearing of about B. 20 deg. S., has a, southerly underlie, and appears to be heaved by the former. The mine has been worked to the 90-fathom level. The lodes varied in width from 2 to 8 feet. The elvans as mapped have been encountered in the mine. The veinstuff is quartz, slate, iron and copper pyrites, mispickel, blende, cassiterite, and stannite. The maximum amount of water pumped from the mine when it was working was over 1,000 gallons a minute. Ding Dong. — There are numerous lodes in this mine having a general bearing E. 25 deg. to E. 30 deg. N., but they are intersected by cross-lodes, guides, or trawns, which heave them, and sometimes themselves carry tin ore (Pigs. 7 to 11). The mine is about 125 fathoms below adit (13 fathoms). When the mine was described by Henwood the principal lodes were Fig. 7. — Ding Dong Mine. ScjouLe. Longitudinal Section of Good Fortune Lode. Bossiliack and Malkins, the former varying in width from 6 inches to 8 feet, while both consisted of quartz, chlorite, schorl, cassiterite, jasper and some earthy brown iron ore. Fluorspar is also a common mineral in the lodes. It is from this mine that Le Neve Foster describes a rock resembling luxuUianite. Hound lumps of schorl rock with roughened surfaces, from 1 to 5 inches in diameter, and consisting of quartz, schorl MINING. 105 Bing Bong Mine. Fig. 8. Longitudinal Section of Bussa Lode. Fig. 9. N. T Longitudinal Section of New Lode. Fig. 10. Longitudinal Section of Malkins and Greenpease Lodes. Fig. 11. Longitudinal Section of Ding Dong Lode. 106 GEOLOGY OF LANDS END. and kaolin (derived from granite), were found in one of the levels.* It is probably to similar rounded lumps that Oarne refers in speaking of ' pebbles ' having been found in Ding Dong.| Tlie maximum amount of water pumped from the mine when working in 1833--35 was nearly 43 gallons a minute. Dbba, Wheal. — Chalybifce and vivianite occurred among the ores of this mine. Bast Wheal Maegaebt (Wheal Merth).— Formerly known as West Poldice. There are several tin lodes now being worked under the name Trevethoe, Limited. When the mine was closed down in 1868, it was at a depth of 77 fathoms. In addition to tin ore there is iron and copper pyrites in the lodes. Bast Eelistian.— Tennantite found with the other minerals of this mine. Edward, Whbal. — This is one of the mines worked under the sea, but it was abandoned in 1856. There are two lodes, both with a north-westerly trend, and according to Henwood one of them is as much as 15 feet in width, although the average width of the workable parts of the lodes is a few feet only, containing limonite, quartz, vitreous copper ore, and copper pyrites, chalybite, tile ore, chrysocolla, malachite, tin ore, chlorite, and schorl, and a little aragonite. Both lodes contained uranium ores (nranite, uranochre, and pitchblende). Bismuth occurs. Elizabeth, Whbal. — Blende, native copper, copper pyrites, melaconite, and iron pyrites occurred in this mine. Plorenob Consols. — Yielded tinstone and mispickel. Garth Mine (or East Wheal Cock). — Situated in the granite south of Beryas Bridge, about two miles west of Penzance. The lode traverses both granite and killas, and strikes E. 25 deg. N. with a southerly underlie. According to Henwood the lode is large, varying from 9 to 1 4 feet. It was worked to a depth of 30 fathoms from surface. A great deal of wood-tin was found in the lode, as also carbonate of iron. Georgia, Whbal.^ — ^Situated in the newer flne-grained granite in the parish of Towednaok. The newer granite was passed through at a depth of 60 fathoms from surface at Flat Rod shaft (Fig. 12). Fig. 12. — Georgia Tin Mines. N. ' . _ i'iD^.of .5^1 o I [ I ScaZe. SOfrns -J I GonoLPHiN MiNB. — There are ^elVeral lodes in this mine having a general south-eastefly bearing with the exception of one or two striking nearly east and west or in a north-easterly direction. According to Henwood the lodes vary from 1 to 6 feet in width down to the 90-fathom level, and contain quartz, earthy limonite, tin ore, copper and iron pyrites, vitreous and native copper, with chlorite and fragments of slate. Great Work Mine. — The lodes of this mine have a general bearing E. 45 deg. N. and have been extremely rich in tin ore. In 1868 the * 'Ircms. Boy. Qeol. Boo. Corn., vol. x., 1879, p. 8. t ' On the Granite of the west part of Cornwedl.' IHd., vol. iii., 1828, p. 208. MINING. 107 principal workings were on. the Great Work, Wheal Breage, and South Wheal Breage lodes.* The Wheal Breage Lode, upon which are sunk the Wheal Kine, Wheal Breage, and other shafts, has a westerly underlie of 6 deg. to 46 deg. and varies in width from one inch to 4 feet.| Quartz, chlorite, tin ore, iron pyrites, mispickel, limonite, copper pyrites, wolfram, and fluorspar occurred in the lode. 2'ftc Great Work Lode has been worked for over 200 fathoms in depth and vaiies in width from an inch to 5 feet, consists of tin ore, black and yellow copper ore, limonite. In the middle of the lode is a quartz vein on each side of which tin ore occurs. The richest place was at the junc- tion of this lode with Wheal Reeth lode. In the Reeth Lode copper and tin ore occurred. The copper ore was both grey and yellow. In the killas on eastern part of the mine no ore has been found. South Wheal Breage Lode varies in width from ^ foot to 6 feet and underlies to the south-east. In the eastern part of the mine the lode was worked to the 135-fathom level and in the western part to 100 fathoms. Large quantities of tin ore were obtained, and copper and iron pyrites and grey copper occurred. There is said to be a cross-course which in West Godolphin and Wheal Precense, in killas, is said to be tin bearing. The line of junction between killas and granite is stated to be irregular and in some cases the granite overlies the killas. GwALLON Mine. — The lode has a bearing a few degrees south of east and underlies south 4 deg. to 12 deg., varying in width from 4 to 12 feet, consisting of slaty material with tin and copper ores (black and vitreous). An elvan is seen in the mine. Heiiland MrMJ^^^cluding Wheal Drannack and Prince George). — The lodes vary in «Krection from K. 20 deg. N. to' E. 35 deg. N., with the exception of one striking N. W. and S.E. They underlie south or are verti- cal, and are all of small width, varying from an inch to 2 feet down to the 152-fathom level. As a rule the lodes could not be depended on to con- tinue productive for any distance, as they soon dwindle and die away or become split up into branches. In fact, the occurrence of the ore was sporadic and uncf rtain. In the Manor old lode the ore occurred occasionally in floors 2 or 3 feet in width. The lodes are heaved by fluccans and cross- courses. The minerals of the lodes are copper and iron pyrites, black copper ore, limonite, mispickel, and wolfram. In addition, there is a silver-bearing cross-course striking N. 30 deg. W. and from the 30 to 152- fathom level underlying E. 18 deg. to W. 18 deg., varying in width from 2 inches to 2 feet. The lode consists of several cracks and contains native capillary silver in cavities with pyrargyrite, silver glance and mis- pickel, bismuth, cobalt, smaltite, and horn silver. According to Phillips, £8,000 or £9,000 worth of silver ore was sold before 1814. The Herland Gaunter lode is said to have been traced for 3 miles. (Came and Henwood.) It contains principally copper and iron pyrites and blende, and was par- ticularly rich at its junction with other lodes. JisNNiNGs Wheal (formerly Parbola). — The mine was chiefly noteworthy on account of the curious occurrence of the tin ore in an elvan. The lode has been described by Henwood:]; and G. Seymour.§ The elvan belongs to the newer east and west non-porphyritic series. In Wheal Jennings the strike is due east and west and the elvan has a southerly underlie. The tin ore occurred in a number of small parallel strings and shrinkage cracks running across the elvan, which is 40 to 80 feet wide. In the vicinity ot the strings the elvan is completely altered and impregnated with ore. The cracks and strings vary in width from 4 or 8 iuches to a size so small that .30 can be counted to the inch. These cracks are sometimes continued into the killas, but generally finish at the wall of the * B. Kitto. Eep. Boy. Corn. PoVy. Soe., 1868, p. 49. t Henwood. Trans. Roy. Oeol. Hoc, vol. v., 1843, Tah. xliiii. t Trans. Boy. Qeol. Soc. Corn., vol. v., 1843, p. 38. § lUd.,yQ\. ix, 1877, p. 185. 108 GEOLOGY OF LAND S END. elvan. Under the IS-fathom level east of William's shaft, the stope was 6 feet in width and yielded 10 per cent, of black tin^ Katlb, Wheal (Phillack). — Down to the 36-fathom level the lode underlies south 4 deg. to 20 deg. and is from 6 inches to IJ feet wide, con- sisting of quartz, limonite, black copper ore and copperpy rites, galena, and chlorite. The lode is heaved by a fluccau and a slide. (Henwood.) Levant Mine. — The mine has been referred to by Henwcod, Carne, Warington Smyth, and otheis. It was visited by the Survey in 1903, who ■tlgirpmg ■tig amxa^ ■'ilgioiBauoso; S3 5; 'Hg'ann&u^ •^igsuariro: "^ggdmPi are indebted to Major White for the facilities he afforded for examining the mine, and to Mr. Leonard Thomas and other underground Captains for much assistance. The mine is worked for both tin and copper, and in the winter of 1903 about 120 tons of dressed copper ore and 40 tons of black tin were being sold each month. It is situated at the margin of the St. Just granite, which at this place is overlain by hornfelsed killas and greenstone (locally ' Iron killas '). The productive ore-ground in Levant is confined to the parts of the lodes traversing the killas and greenstone while in the granite, except in the upper levels, the lodes are barren! (Pigs. 13 to 19.) The lodes are narrow in comparison with those of other districts, but contain a variety of minerals such as bismuth MINING. 109 bistniithinite, carbonate o£ bismuth, malachite, native copper, fahlerz, arseniate of iron, aragonite, gothite, garnet, g7psa(n, native silver, scheelite, tetrahedrite, cuprite, and mispickel. The most northerly lode in the sett is the Prince of Wales lode, which was intersected by a cross-cut driven north from the North lode along a guide or cross-course near the Old Submarine shaft at about the 110 GEOLOGY OF LAND S END. Fig. 15. — Levant Mine. Diagramitiatie Sketch showing the Eelation of the Ore to to the Granite. Fig. 16. — Levant Mine. Fig. 17. — Levant Mine. s.w-l 1. 5 -i^i N.E. "^ hc7o*r .sea JflOO. S.W. N.E. Cross Section at Skip Shaft. mOOfeet heZory SK^L Section at Old Submarine Shaft. Fig. 18. — Levant Mine. S.W. N.E. 1 Sea ^"1 600 "^ "i^izoo '^1 %ijSOO reei. Section at New Submarine Shaft, Fig. 19.- S.W -Levant Mine. N.E 600 -moo ±800 feet, Leyvi- Section on the North-West of the New Submarine Shaft. MINING. Ill 170-fathom level. It was again met with in the deep workings about the 300 -fathom level near the New Submarine shaft, where it forms a junction, in going westwards, with the South lode. It has a bearing of N. 72 deg. W. and a southerly underlie. The lode, 15 inches wide, contains tin and copper ores with plenty of mundic. Where it was encountered in the deeper workings the lode was 4 or 5 feet in width and almost valueless. The North Vein is situated about 150 fathoms south of the Prince of Wales lode, is nearly parallel to it, and has a northerly underlie. It forms a junction with the North lode in going westwards a little west of the Old Submarine shaft near the 300-fatliom level. It has been a fairly pro- ductive lode, and during a depression in tin about £25,000 worth of tin ore were raised from it, whiuh helped the mine through a critical period. The North Lode is the next on the south and is one of the main lodes of the mine. It meets and cuts across the South lode in going westwards and as it became poor the lode has not beeii followed further. It has a bearing of W. 28 deg. N. and a southerly underlie of 20 deg. The ore is confined to a leader consisting mainly, of Cfuartz with occasionally fluorspar up to 18 inches in width. This lode, seen in granite in the deep levels, was small and poor. The lode has been worked for years in the greenstone country, and the occurrence of copper and tin is remarkable for its association at the 200-fathom level with a cinnamon-coloured garnet vein which occurs in the lode in the same manner as a quartz vein does. The Old Bal Lode it the next ou the south. In the old part of the mine, inland, it was the main lode, but near the Skip shaft it branched, going westwards. The northern branch, still called the Old Bal lode, has not been worked far seawards. The southern branch is the South lode. It was rich in tin and copper ores in its upper levels but poor in depth. At the Guide shaft the bearing is N. 30 deg. W. but under the sea the bearing is N. 23 deg. W. Underlie N. 20 deg. The Guide which runs through Carnyorth Moor appears to be a continuation of the Old Bal lode. The next lode is the Boscregan lode, which branches off from the Old Bal lode eastwards and crops out in Levant Zawn. According (o Henwood there are three Boscregan lodes— the Boscregan North, Middle and South lodes respectively. They contain jaspery iron ore, limonite, hicmatite, and cassiterite. The Shop Lode. — Like the guides it has a north and south direction and a westerly underlie. It consists of limonite, quartz, and vitreous copper ore. It crops out in Zawn Bunny, and inland it cuts the Old Bal lode near Boscregan shaft. The South Lode is at present the main lode of the mine. Eastwards it runs into the Old Bal lode. The general bearing is N. 40 deg. W. with a northerly underlie. The 278-fathom level has been driven sea- ward over 850 fathoms or about a mile. On the east of the intersection with the North lode it is about 2 feet in width and contained tin, copper ore, and zincfolende. Near the actual junction it was very rich, and a most profitable bunch of copper ore, which was called the ' Yankee Goose,' was worked out. Near the 338-fathom level the copper pyrites is mixed with garnet, which, in the dim light of the miner's candle, has been mistaken for tin ore and sent to surface as such. Locally it is known as 'spelter.' The lode has been explored westwards under the sea for al)out a mile and contains rich shoots of tin and copper ore and varies from one to five feet in width. Guides. — There are several cross-courses or guides with a general bearing E. 13 deg. S. and in width about 2 feet. Near the Old Submarine shaft the guide contains nodules and rounded fragments of the county rook (greenstone) embedded in an argillaceous matrix. It appears to be a crush conglomerate. Although the main workings are situated below the sea, the mine is very dry. In the old days, before the mine was so deep, an occasional panic was caused by unexpected flows of sea water finding a way into the working places, and Oarne states that stones could be heard rattling on the sea bottom at the time when the mine was only 42 fathoms deep.* A * ' Mineral Productions of St, Just.' Trans. Soy. Geol.Soc. Corn., vol. u.,lS22_ 112 GEOLOGY OF LAND S END. panic was caused in 1852 by sea water breaking into a winze above the 40-fathom level at 150 fathoms west of the Engine shaft. In 1857 the man-engine was put in to enable the miners to get to their work without loss of time or undue fatigue. This man-engine is still in use. Owing to the distance of the deep workings seawards, two submarine shafts were construotfed to obviate the necessity of making long haulage tunnels from the skip shaft. In this way the material broken in the deep workings is wheeled to the bottom of the 'New Submarine ' shaft and hauled up to a level leading to the ' Old Submarine ' shaft, up which it is hauled to another level leading to the bottom of the Skip shaft, through which it reaches the surface. The temperature in the deepest workings is 91 deg. F. About 270 gallons of water ppr minute is pumped from the mine. Annual Output from Levant Mine since 1820. Year. Black Tin. Copper Ore. Copper. Year. Black Tin. ; Copper Ore. Copper. Tons. Tons. Tons. Tons. Tons. Tons. 1820 *.. 1,290 192 1863 170 1,203 85 1821 1,188 210 . 1864 184 839 54 1822 ... 293 31 1865 183 009 42 1823 319 33 1866 195 349 20 1824 ... 334 28 1807 187 376 37 1825 107 14 1868 135 380 35 1826 176 22 1809 174 142 19 1827 415 50 1870 139 100 10 1828 ■ •• 581 58 1871 86 72 9 1829 ... 850 96 1872 40 1830 1,246 173 1873 84 "74 "s 1831 • ■■ 1874 150 61 12 1832 ... 1,188 1875 196 123 18 1833 ... 1,286 ... 1870 248 338 42 1834 ... 1,487 ... 1877 260 402 50 1835 .*. 1,967 ... 1878 233 741 101 1836 ... 2,345 1879 274 385 45 1837 56 ... 1880 227 519 70 1838 78 ... ... 1881 232 1,002 124 1839 08 3,005 ... 1882 230 1,173 117 1840 ... 2,475 ... 1883 283 1,477 155 1841 ... ... 1884 317 1,637 216 1842 ... 1885 452 1,.304 153 1843 ... 1886 456 034 85 1844 ... ... ... 1887 492 727 105 1845 ... 1,088 100 1888 437 1,209 176 1840 ... 1.293 130 1889 451 1,505 210 1847 851 99 1890 475 1,979 230 1848 ... 1,776 178 1891 478 2,189 230 1849 ... 1,904 171 1892 499 1,719 216 1850 ... 2,668 217 1893 665 1,236 140 1851 ... 1,539 118 1894 629 1,882 250 1852 57 1,333 102 1895 517 4,333 408 1853 41 1,G27 91 1896 422 4,897 470 1854 287 1,589 88 1897 572 3,455 351 1855 310 1,678 95 1898 550 2,981 200 1850 218 1.041 94 1899 551 3,027 250 1857 192 1,587 82 1900 464 5,064 300 1858 151 1,473 97 1901 514 3.550 230 1859 210 1,.507 90 1902 573 3,050 160 I860 227 957 57 1903 .502 3,381 170 1801 179 907 62 1904 540 2.884 130 1862 J 90 1,069 71 1905 528 3,387 271 MINING. 113 Lblant Consolidated. — Down to the 100-fathom level the lode varies in width from a mere parting to 1-^ feet, and contains quartz, earthy haematite, cassiterite, and tourmaline. Little Bounds Tin Mine (part of St. Just Amalgamated). — Three lodes in this mine were worked beneath the sea, the noise of which could be heard from the workings. In a level on Savealls lode an accidental com- munication was made into the sea, but no permanent damage was done. The lodes varied from a few inches to 5 feet in width, and consisted of chlorite and tin ore, quartz and tourmaline, with limonite. The mine is situated at the junction of granite and killas. Mabazion Mines (Wheal Virgin, etc.). — The Virgin Lode has a bearing a few degrees south of east and underlies S. from 15 deg. to 45 deg. Down to the 100-fathom level it varies in width from 1 to 8 feet, and consists of quartz, tinstone, limonite, iron pyrites, melaconite, and copper pyrites, and also a vein of blende. There is another called the Crab lode. (Hen wood.) According to Lean, in 1833-5 the maximum amount of water pumped from the mines was about 442 gallons a minute. Wheal Maegebt.— Situated between Trelyon and the sea coast. In 1857 copper ore was being worked beneath the foreshore in this mine, while in 1859 the 80-fathom level, which at this time was the deepest, had been driven 18 fathoms beyond the low-water mark seaward, near the American shaft. The American shaft, which has an incline seawards, was sunk to the 154 in 1866 and was afterwards carried down to the 165. The workings are all on one lode of small size which is not rich. Copper was yielded mainly in the upper workings, but the lode became stanniferous in depth. The lode was more productive inland. Iron pyrites was also raised. Mellanear. — Copper pyrites, tinstone, zincblende, and iron p5'rites raised. (Fig. 20.) Fig. 20. — Mellanear Mine. Mkllanowbth. — Anglesite and galena occurred in the gossan of, this mine below which copper was found. MiLLBT, Wheal. — Copper pyrites yielded. MoEVAH AND Zbnnob UNITED. — Situated near Rosemergy Cliffs in the parish of Morvah. (Pig. 21.) According to Henwood, two lodes intersect- ing each other nearly at right angles have been worked down to the 60-fathom level. They contain quartz, tourmaline, iron pyrites, hsematite, chlorite, and tin ore. A trawn (guide or cross-course) 2 to 3 fathoms in width runs parallel to one of the lodes. Nanoecothan and Avback Consols (Sanereed). — According to_ an unpublished report there are eight lodes with bearings in different direc- tions. 9564 * 114 GEOLOGY OF LAND S END. Neptune. — Malachite among minerals found. New Eosewarne. — Copper pyrites, mispiokel, chalcedony, pearl spar, semiopal, jasper, and dolomite, recorded from this mine. Fig. 21. — Morvah Consols. NoETH Battbkt Tin Mink. — According to an unpublished report by Warington Smyth, this mine is situated near St. Ives Head. A level has been driven for a distance of 20 fathoms under the sea at a depth of 7 fathoms. Wheal Owms and Boscean Mine. — Wheal Owles has been worked to the 130-fathom level and Boscean to a depth of over 78 fathoms, mainly for tin ores. Mispiokel and uranium, chalybite, chrysocolla, diallogite, mala^ ohite, pharmacosiderite, pitchblende, torbernite, gSthite, specular iron ores occurred in this mine. Other minerals found were calcite, aragonite Wheal Owles. — Wheal Boys Guide Lode. 135 fm,le»^ei. (rose lime), vivianite, and zippeite. Wheal Owles ceased working suddenly owing to an accident in which twenty men lost their lives about nineteen years ago. The accident was caused by a neglect to compensate for annual magnetic variation in making the plans, with the result that a level was unsuspectingly driven too near an old mine filled with water. The water burst through and flooded Wheal Owles. (Figs. 22 and 23.) Parknowbth.— According to Henwood there are nine lodes in the sett, all of them luiving a general north-westerly trend (W. 30 deg. N.). In width they vary from a few inches to 4 feet down to the 84-fathom level, and consist of quartz, hsematite, limonite, chlorite, tourmaline, kaolin, cassi- terite, and rarer minerals, as phosphate of iron, etc. The guide has a bearing of N. 30 deg. W., and at the 54-tathom level is 9 to 1§ feet i^ width, consisting of quartz, limonite, specular iron ore, etc. MINING 115 Pbnbbrthy Ckobts. — Pyromorphite has been recorded among other minerals from this mine. The mine yielded both copper and tin ores and some lead. Pendken Consols. — Previously to 1859 the shallow levels were worked but were proved to be poor. In depth, however, the lode improved, and the 82, 106, and 118-fathom levels we're driven seaward. The 85-fathom level was driven seaward 90 fathoms beyond high-water mark. It intersected the great quartz lode which passes between the Kenidjacks and the main- land, which was found to be barren and to consist of quartz and iron pyrites. The sea water made its way into the workings freely. In 1865 the mine was 154 fathoms in depth, and yielded a little tin and copper ore. The lode strikes due north and south and can be traced through to Boscaswell. There are several silver-lead veins outcropping in the elifE westwards, having a general north-westerly bearing. PoLLADBAs DowNs. — The mine is north of Wheal Vor. There are several lodes shown on the map, some of which were referred to by Henwood. They all underlie nortli, and down to the 83-fathom level con- tain tin ore, iron pyrites, and other minerals. The lodes are heaved varying amounts up to 14 fathoms by the great fluccan. Fig. 23. — Wheal Owles. — Gargodna part. rH"-'-^ ^ /hvlt^el Praze Tin Mine (near Bosvvedden).— At 20 fathoms below high-tide mark a level is driven under the sea 20 fathoms. The lode has not been worked since 1780*. Prosper, Wheal, ores of copper. •Melanterite has been found in this mine with other Prospidniok.— Wolfram occurs with tinsione. Providence Mines.— These include Wheal Speed, Wheal Providence, and other small mine setts. According to Henwood there are two principal lodes, the Laity and the Comfort, the former dividing westwards into the North and South lodes and having a strike E. 20 deg. N. The latter strikes N. 15 deg. W., and has been explored down to the 150-fathom level. Both lodes contain tin ore, vitreous copper, copper pyrites, and native copper, chessylite, cuprite, connellite, clinoclase, chalcedony, liroconite, mispickel, melaconite, malachite, torbernite, chlorite, limonite, tourmaline, iron pyrites, etc. Connected with the Comfort lode at 105 fathoms below surface (or 65 below adit) there is a carbona which is south of the intersection between the Laity and Comfort lodes. It consists of quartz, felspar, schorl, and tin * J. Came, ' On the Mineral Productions of St. Just.' Corn., vol. ii., 1822, p. 290. 9564 Trans. Sny. Qeol. Soc, I 2 116 GEOLOGY OF LAND'S END. ore, and is 15 feet wide, n fathoms long, and from 4 or 5 feet to 5 or 6 fathoms in height. The carbona goes vertically downwards and dies out, and is connected to the Comfort lode by strings and pipes. According to Penberthy* there was a North and a South lode, both ex- plored to over 100 fathoms below adit. The pitchblende which was dis- covered in the mine was first found at the 20-fathom level and then at the 40, which extends seawards 105 fathoms. In the main lode the pitchblende was seen above the 30-fathom level under the sea at about 200 fathoms from the place in which it was found in the South lode. According to Lean a maximum of over 113 gallons a minute were pumped from the mine when it was working.j Pkovidenoe, WHBAii (Gwiuear). — Uranite and argentiferous mispiclsel occurred. Bebth, Wheal. — Copper glance found. Eblistian Mine. — The lodes were largely in one of the newer east and west elvans ( 1 1 fathoms wide) of the same general character as that at Wheal Jennings. Some of the excavations in the mine are as much as 30 feet in width. Henwood states that the mine was worked to the 155- fathom level and yielded tin ore, mispickel, wolfram, iron and copper pyrites, vitreous and native copper. In the North lode at the 105-fathom level " globular masses of felspar " are stated to have been found ; also a conglomerate of slate fragments cemented by oxide of tin and copper ore. The mine was working as far back as 1715.J The maximum amount of water pumped from the mine when it was working, about 1835, was nearly 140 gallons a minute. KiBLOWs.- Several veins can be seen cropping out in a granite ledge above the shore below Ballowall Cliff. They are a continuation of the lodes which were worked on Hermon Hill, and were being worked in the early part of last century. Retallaok Mine. — Down to the 53-fathom level the lode is 4 inches to 2 feet in width, consisting of limonite with black copper ore and copper pyrites. The lode is heaved 7 fathoms by a fluccan. (Henwood.) An elvan traverses the sett. Rosewabne Mine. — Copper pyrites, tinstone, and opal occur. EosE AND Penbose. — Limonite and argentiferous galena. Nearly 350 years ago galena from Wheal Rose contained 30 to 40 ozs. of silver per ton, and from Penrose 60 ozs. per ton. St. Atjbyn and Geylls. — As seen on the map there are two series of lodes, the principal of which has a south-easterly bearing, while the other has a north-easterly bearing. According to Punnett§ the main lode passed from killas to elvan in which some curious deposits of tin were met with from the 50 to the 60-fathom levels. One of these was a cylindrical shoot 9 inches in diameter and about 2 fathoms in length. Other shoots were met with at the (50-fathom level up to 3 fathoms in length. Although principally worked for tin, some of the lodes contain copper ore and arsenical pyrites. St. Ives Consols. — This mine is chiefly noteworthy on account of its remarkable deposits of tin ore known as carbonas. Similar irregular or pipe-like deposits were found in Rosewall Hill and Ransome United Mine. The following notes are from Henwood and Salmon. || The main or standard * ' Note on the Discovery of Pitchblende at Providence Mines.' Trans Roy. 6eol. Soc. Corn., 1846, p. 106. t According to Henwood, the total receipts by sales of ore in the 36 years before 1871 amounted to £405,367. Working costs, £312,071. Lords dues £14,780. Total, £326,851. Profits, £78,516. t J. S. Courtney. Hep. Corn. Poly. Soc, 1836. § H. Macaulay Punnett. ' On some Peculiar Deposits of Tin Ore ' Trani Roy. Geol. Sob. Corn., vol. vii., 1847-65, p. 379. • / «». II H. C. Salmon, Mining and Smelting Magazine, 1863, p. 139, MINING. 1 17 lode, which is the principal lode of the mine, runs along the bottom of the valley leading to St. Ives, and in 1863 this lode had been worked upon to a depth of 197 fathoms from surface or 177 below adit. The lode contained mainly tin ore with peach (chlorite), tourmaline, and quartz, but there was also a little haematite, bismuth, cyanosite, cuprite, limonite, vitreous copper ore, and iron pyrites. The average width of the lode was about 2^ feet, and it is nearly vertical. The other lodes which were worked are William's, Kemp's, Daniell's, and Alexander's. There are two cross-courses or trawns which heave the standard lode 6J and 8 fathoms respectively. The great carbona appears to have been formed at the junction of a series of east and west lodes with a north and south vein or cross-course called Kemp's lode. It is a pipe-like mass, with a general north and south bear- ing, consisting of schorl, tia ore, chlorite, fluor, and copper and iron pyrites, and the change in the character of the rock in passing from the carbona to the country rock is gradual. The carbona had an average height of 4 fathoms and was about 2 fathoms in width. It was very irregular and had several branches. Gilbert* describes a vugh which was met with at the 167-fathom level in the most southerly or Daniell's lode. It was 15 feet in length, about 12 feet in widest place, and 10 feet in height, and was lined with quartz crystals and yellow copper ore. The maximum amount of water pumped from the mine when working in about the year 1835 was nearly 135 gallons a minute, according to Lean. St. Jcst United and Cape Cornwall Mines.— Worked below the sea for many fathoms. Melaconite, copper pyrites, vitreous copper ore, etc. Spbabn, Wheal. — According to Henwood there are nine lodes varying in width from a few inches to 2 feet. There are two principal lodes in this mine. One appears to be a, continuation of the Old Bal lode in Levant, and the other has a more or less east and west direction through Spearn Moor Mine to Roscommon Cliff. It has a southerly underlie. The lodes contain mainly tin ore with iron pyrites, fluor, chlorite, mispickel,and other minerals. A little melaconite, cuprite, vitreous copper ore, native copper, fahlerz, jasper, were also found. Strawberry, Wheal (Crowan), known also as Wheal Julia. — The lode strikes in a south-easterly direction, and has a southerly underlie. Con- tained mainly copper and- iron pyrites, black copper ore, and blende. Speedwell, Wheal. — The 30-fathom level has been driven below the sea on a copper lode. Tbebn Copper Mine (Gurnard's Head Mine). — A level has been driven at 13 fathoms below sea level. It goes eastwards of the shaft a distance of 20 fathoms and westwards 10 fathoms. The shaft is not far above the sea. TbannaOK. — Copper pyrites, vitreous copper, and tinstone occurred. Tregurtha (Pig. 24).-Carbonate of bismuth p 24>.—TrequHha occurred in the tin lode. _ ,,.'' „ m J. i- J i- -1 Uowns Mtnes. Tbbmaynk. — Toads-eye tin and native silver found with copper ores. Greenstone has been met with in the part of the mine now called Wheal Hampton — at the 32-fathom level in Clark's shaft. Trenwith, Wheal. — Situated on the south side of the valley immediately west of St. Ives. The lodes belong to the series worked in St. Ives Con- sols. The lodes yielded both copper and tin ore, while at the 35-fathom level pitchblende was found. Copper glance, cuprite, melaconite, ery- thrite, haematite, and torbernite. Trevaskus. — Blende, tinstone, native copper, copper pyrites, chalybite, mispickel, galena, ten- nantite, fahlerz, fluorspar, dolomite, and chalcedony found in this mine. • J. Gilbert. IVms. May. Qeol. Soo. Corn., vol. ix., 1864, p. 158. "a-i 118 GEOLOGY OF LAND's END. Carew*, in his Survey of Cornwall (p. 21), states that the miners " meet sometimes with ore [native copper] so rich as to be malleable, sometimes powdered with sparks throughout and sometimes -with the same in leaves so thai it may be twisted round the finger ; but this only in small quantities." Tkbwavas, Wheaii.— According to Henwood there are four lodes vary- ing in width from 1 inch to 6 feet, and yielding copper pyrites and copper glance with other minerals. Tbbwidden Bai. — Situated near the margin of the granite. The tin ore occurred in 'floors,' which, according to Hawkins, underlie northwards. This writer states that each ' floor ' occurred in a white porphyritic rook, varying from 2 to 3 feet In thickness, and alternating with layers of killas. These floors are intersected by several lodes from which, no doubt, the minerals of the ' floors ' were derived. Quartz and schorl accompanied the tinstone. Unitt, Wheal. — A great variety of minerals were found in this mine. Asbolane, blende, native copper, copper pyrites, liroeonite, mispickel, mimetite, scorodite, ohessylite, malachite, olivenite, marcasite, pharmacosi- derite, molybdenite, tennantite, chrysooolla, clinoclase, connellite, cuprite- erythrite, fluor, jasper, and iron pyrites. West Wheal Darlington. — Silver ores occurred in an east and west lode containing quartz, slate, yellow copper ore, ohalcopyrite, galena, argentite, and native silver at 40 fathoms from surface. West Godolphin.— Melaoonite, blende, malachite, copper glance, galena, and iron pyrites are recorded aimong minerals from this mine. WherbY Mine. — The early history of the working of this mine has been told by John Hawkins.j The old mine is situated on the Wherry Rocks on the coast near Penzance. The place at which the tin veins occurred was covered by the sea, except at low water, so that work could only be carried on intermittently. The tin ore occurs in veins in an elvan which has a strike of E. 45 deg. N. Some parts of the elvan were much impregnated with tin ore, so that the whole of it was worth raising. The mine workings are entirely in the elvan which is 18 feet wide, according to Hawkins, although Dr. Forbes states that the mine was 90 feet wide.J Among the flrst operations was the sinking of a pump shaft. The sea water was kept back by a watertight board partition 20 feet high and 2 feet square, kept in position by iron bars. In 1791 the workings were 18 feet in width and the shaft 4 fathoms la depth. In 1792 a trestle bridge was constructed between the mine and the mainland, while the mine was kept tree of water by pumps connected with an engine-house on the mainland by a line of rods. This structure was carried away by a ship which broke its moorings during a storm, but not before £70,000 worth of tin ore was raised from the mine. Borlase states that several tons of cobalt ore were also obtained. West Tolvaddon. — Situated on the rock coast between Newlyn and Mousehole. The workings are down to the 30-fathom level beneath the foreshore, but the lode, although containing a little copper, is poor. Opera- tions were commenced in 1859 and suspended in 1863. Violet Seton. — Situated on the west of West Wheal Seton. At the 100-fathom level the lode was 4 feet wide, and contained blende, lead, and copper, but lode was poor. * With Addenda by Thomas Tonkin in 1811. + 'On Submarine Mines.' Trans. Boy. Geol. Soc. Corn., vol. i., 1818, p. 127. T ' On the Land's End District.' Ibid., vol. ii., 1822, p. 242. MINING. 119 MISCELLANEOUS SECTIONS OP MINES. Fig. 25. — East Tregembo Mine. N. Fig. 26. — Whml Friendshvp. -LBOfm, Fig. 11.— Great Wheal Fortum. 120 GEOLOGY OF LANDS END. MISCELLANEOUS SECTIONS OP MINES— cont. Fig. 28. — Oreat Western Mime. 1 p IS "^ SI'S "5 -If Longitudinal Section of Kendall's Lode. Fig. 29. — Owm and Singer Mine. O SOnna " I i_j I l__J Fig. 30.— FAeai Hewrle. N. SO fin Fig. Sl,—r8ithn^ and Ga/mmeal Mine. N. MINING. 121 MISCELLANEOUS SECTIONS OP MINES— cont. Fig. 32.— South Wheal Fig. 33 Tmdene Mime. Speed. Longitudinal Section of the Gaunter Lode. Fig. 34. — Treloweth Mme. W. ,SS>S E. Fig. 35. — Worvas Downs Mimes. 122 MINERAL STATISTICS. General Statistics. For purposes of comparison the general statistics relating to the output of the mines comprised in the 1-inch maps 351 and 358 may be grouped so as to represent the principal mineral areas. The figures representing the output are incomplete owing to imperfection of the record, and they only refer to the yield of ores during certain stated periods. The totals for copper are from published statistics since 1815 ; and for tin since 1852, with the exception of one or two years before 1840. For lead, zinc, arsenic, iron, etc., the figures do not go further back than 1 854. g O 1 1 1 Crude and Eeflned Ar- senic. 1 i % Hi St. Just District. Whitesand Bay to Morvah Tons. 57,600 Tons. 133,400 Tons. 13,370 Tons. 3,950 Tons. Tons. 5 Tons. 4 Gwinear District and St. Hilary. East of line joining Marazion and the mouth of the Hayle Eiver 29,000 353,000 28,500 400 1,900 120 70 St. Ives District. St. Ives, Trencrom, Canon's Town, etc. - 28,000 38,000 3,050 12 5 3 Penzance District. Immediate neigh- bourhood 1,000 36,000 2,950 5 - . Total . . . 115,000 557,000 47,600 3,717 1,900 130 77 In addition to these statistics the output of black tin from the isolated mines of Ding Dong and West Ding Dong may be put at nearly 3,000 tons. Silver has been produced in some quantity, principally in the Gwinear district and the region to the south. In St. Ives a little silver has been raised. At St. Just some iron ore (75 tons) was wrought ; and in Perranuthnoe and Crowan over 1,800 tons, while ochre has been obtained in St, Ives. Two hundred and fifty tons of iron pyrites, or sulphur ore, has been raised in the Gwinear district, and about 33 tons in the St. Ives district. MINERAL STATISTICS. 123 Output of Copper Ore from 1816 to 1905, In 1865, 1866, and 1867. BinnerWood - ... 470 36 From 1822 to 1824 ; and in 1854 Binner Downs - 51,100 3,770 From 1819 to 1838. Boiling Well - 2,990 170 From 1854 to 1861. Be- 930 65 tween 182] and 1856, 2,157 tons of ores con- taining 142 tons copper were yielded (Phillips and Darlington). Bolton, Wheal- 1,630 135 From 1824 to 1826. Bosoaswell and 1,925 700 64 In 1837 and 1841 and from Boscaswell 315 • • t .,, 1851 to 1875, including Downs tin in 1838. Boscean - 2,400 284 ... In 1837, 1838, and 1839, and from 1852 to 1869. Bosorn and 75 ■ •* In 1837, 1838, 1839, 1841, Ballowall 1853, and 1854. Boswedden and Castle 1,375 117 200 20 In 1837 and 1841 and from 1853 to 1872. 124 GEOLOGY OF LAND S END. Name of Mine. Total yield in period stated, and largest amount raised in one year during that period. Black tin. Copper ore. Copper. KemarkB. Bosworgy. Botallack and Carnyorth Brea Consols - Cape Cornwall and St. Just Consolidated Carbona Mine Carne, Wheal - Carneiloe Mine Carn Galver - Carnyorth (bo- fore amalga- mation with Botallack) Caroline, Wheal Carpenter, Wheal Carriok Du Carzise - Castle, Wheal (part of Bos- wedden and Castle) Christopher, Wheal, and Christopher Consols Chypraze Consols Clowance, Wheal Tons. Tons. 25 ..• 14,040 20,290 501 1,274 75 ..• 18 ... 7 85 6 150 38 ... 1,050 ... 137 ... 9,830 ... 2,400 ... 1,230 5 1,120 398 185 2,360 10 16 60 ... 25 ... ... 830 Tons. 2,446 140 630 156 77 74 26 225 82 In 1874, 1875, and 1876. From 1815 to 1835; in 1837 and 1841 ; and from 1845 to 1905. Between 1815 and 1856, 20,276 tons of ore containing 2,552 tons of copper were raised according to Phillips and Darlington. Some black tin raised in 1838. Between 1860 and 1863. Between 1865 and 1867. In 1852. Between 1852 and 1856. In 1872 and 1873. In 1860 and between 1871 and 1876. Prom 1853 to 1865. Between 1826 and 1831. Between 1853 and 1855. Between 1856 and 1860. From 1825 to 1827 ; in 1838, 1839, and 1873. Some tin ore in 1837. Between 1820 and 1842, 4,128 tons of copper ore containing 363 tons of copper were raised. Tin ore in 1838 and 1886. Copper in 1821. In 1857 and 1858. In 1852 and 1853. In 1815 and 1816. MINERAL STATISTICS. 125 Name of Mine. Total yield in period stated, and largest amount raised in one year during that period. Cock, Wheal Crebor, Wheal- Crowan Consols (Wheal Dumpling) Cunning, Wheal (formerly Bos- wedden and Castle) Darlington, 'Wheal Ding Dong Drewlas, Wheal Durlo Bast Alfred Consols East Balles- widden East Bosoas well Bast Bosom East Botallack- Bast Wheal Cook (Garth Mine) East Godolphin East Wheal Grylls East Hallaman- ning Bast Wheal Kidney Bast Levant - East Wheal Margaret East New Rose - warne EastProvidenoe East Belistian- Black tin. Copper ore. Copper. Remarkg. Tons. 8 Tons. 2,175 Tons. 226 ... 1,000 210 68 9 355 96 ... 416 142 18,900 1,405 2,905 268 462 99 4,270 3,349 1,490 416 330 102 15 ... 65 1 6 60 500 10 42 168 100 5 10 ... i ... 25 775 92 25 ... 87 100 "i From 1821 to 1832. Black tin in 1841. Between 1827 and 1830, and in 1832 and 1835, 1,140 tons of ore containing 117 tons of copper were pro- duced. Between 1852 and 1854. Prom 1863 to 1866. Prom 1872 to 1876. Copper between 1833 and 1845. Prom 1833 to 1836 ; In 1838, 1839, 1840, and 1845, 10,100 tons of ore containing 450 tons of cop- per were yielded. Some of the tin raised in 1838 and 1839. From 1855 to 1878. In 1821 and 1822. Between 1859 and 1864. Prom 1857 to 1863. In 1852 and in 1873 and 1874. Prom 1872 to 1875. In 1854. From 1881 to 1885. In 1823 and 1824. In 1851. From 1862 to 1866. In 1852, 1855, and 1856. In 1901. In 1837. Prom 1852 to 1864. In 1872, Prom 1863 to 1871. In 1847. 126 GEOLOGY OF LAND's END. Name of Mine. Total yield in period stated, and largest amount raised in one year during that period. Black tin. Copper ore. Copper. Remarks. East Rose- warne East Straw- berry East St. Just United East Tregembo East Trenoweth Edward, Wheal Florence, Wheal Florence Consols Friendship, Wheal J'riendship and Prosper Garth Mine (see East Wheal Cook) Georgia Consols Georgia Tin and Copper Mine Gilbert, Wheal Gilmar, Wheal Godolphin Goole Pellas Great Wheal Alfred Great Wheal Fortune and others Tons. 2 3 20 140 12 2 22 95 14 170 1 23 15 10 526 3,055 417 Tons. 7,240 600 955 42 17,080 Tons. 702 40 100 4 1,597 125 8,425 800 21,510 2,782 5,200 3,143 1,144 158 426 258 From 1857 to 1873. From 1834 to 1837 and in 1841. In 1867. From 1884 to 1894. In 1877. From 1821 to 1856. In 1862 and 1863. In 1873, 1874, and 1875. From 1815 to 1819 ; 1849 to 1855. According to Phillips and Darlington 11,138 tons of ore con- taining 811 tons of copper were yielded between 1815 and 1824. In 1852. From 1852 to 1855. In 1873. In 1838 andJn 1890. In 1856 and 1857. From 1815 to 1818 ; 1838 to 1840; 1845 to 1847. Tin in 1839. According to Phillips and Darling- ton between 1815 and 1846, 9,803 tons of ore containing 936 tons of copper were raised. From 1877 to 1881. 65^1 metallic tin. Prom 1852 to 1863. In 1836 and 1838 and from 1855 to 1891. Wheal Fortune men- tioned by Phillips and Darlington, yielded 52,792 tons of ore con- taining 3,656 tons of copper between 1821 and 1852. MINERAL STATISTICS. 127 Name of Mine. Total yield in period stated, and largest amount raised in one year dnring that period. Black tin. Copper ore. Copper. Remarks. Great Godol- phin Bridge Great Wheal Grylls Great Treve- gean Great Western Mine " Great Work and Great Work Con- solidated Grey, Wheal Grylls, Wheal Grylls, Wheal Florence Gurlyn, Wheal Gurnard's Head G uskas and Anna(Priend- ship) Gwallon - Gwinear Con- sols Gwin and Singer (Breage Mine) Halamanning and Croft Gothal Halamanning and Eetal- lack Hampton, Wheal Hartley, Wheal Hawkes Point - Hayle Valley - Hearle, Wheal Herland, Wheal Hermon, Wheal, Carnleskis, and South Wheal Rose Hopes, Wheal Tons. ■ 1 1 2 20 412 6,256 359 95 683 253 12 180 753 10 16 1* 12 210 53 Tons. 1,020 6 "e 475 25 9,127 512 142 13,400 2,947 9,550 7 670 20 18,520 Tons. 26 75 36 3 520 24 885 197 640 28 2 2,000 In 1870. In 1864. From 1873 to 1876. From 1870 to 1873 and in 1886. From 1832 to 1836; in 1839 and 1840; and from 1849 to 1902. Some of the tin in 1837, 1838, and 1839. In 1838, 1839, and 1903. Fronj 1862 to 1867. In 1865 and 1866. From 1848 to 1852 and in 1904. In 1835. In 1852 to 1866. In 1837. In 1847 and 1848. From 1885 to 1895. From 1851 to 1858, From 1832 to 1836. In 1904. In 1864 and 1866. From 1851 to 1853 ; and in 1883. In 1863. From 1861 to 1864. Prom 1816 to 1843. Be- tween 1832 and 1836, 4,210 tons of ore con- taining 303 tons of cop- per were produced. In 1837 and 1841 and from 1873 to 1878. In 1825. 128 GEOLOGY OF LAND's END. Name of Mine. Total yield in period stated, and largest amount raised in one year during that period. Black tin. Copper ore. Copper. Kemarks. Jennings, Wheal Kayle, Wheal - Kelynaek Keneggy- Kitty, Wheal (otherwise Polpeor, part of Wheal Sisters) Lambo Lamin Leeds, Wheal - Leedstown Con- solidated Leeds and St. Aubyn Lelant Consols Lemon, Wheal Levant Mine Lewis Mines - Locke, Wheal - Lucy, Wheal - Marazion Mine's Margaret, Wheal Margery, Wheal Mary, Wheal - Mary and Kitty United Mary and Tren- crom Mellanear Millpool Tons. 220 3,160 277 770 106 144 32 17,430 665 1,145 262 2 24 326 3,340 362 100 3,940 255 60 230 80 525 Tons. 575 366 520 9,000 500 1,800 115,400 4,897 30,000 16,400 1,932 1,540 66,410 fi.741 Tons. 52 is 30 SIO 36 130 10,775 470 2,222 840 96 100 3,965 455 In 1875, 1876, and 1877 ; and from 1882 to 1884. From 1826 to 1846. In 1901. In 1854 and 1858. From 1834 to 1837 and 1852 to 1875. Some black tin in 1838 and 1839. According to Phillips and Darlington 1,012 tons of ore con- taining 80 tons of cop- par were produced be- tween 1834 and 1856. From 1815 to 1824 In 1823, 1824, and 1825, and in 1832. Prom 1837. to 1841. In 1901 and 1902. From 1857 to 1871. From 1853 to 1857. In 1855. From 1820 to 1841 ; 1845 to 1905. According to Phillips and Darlington 53,815 tons of ore con- taining 6,505 tons of copper were yielded be- tween 1821 and 1856. Prom 1852 to 1861. In 1894. In 1872 and 1873 and in 1893, 1895. From 1830 to 1841. Black tin in 1838, 1839, and since 1852. From 1855 to 1875. From 1854 to 1870. From 1837 to 1839; and from 1848 to 1876. Some tin raised in 1838, 1839. From 1860 to 1862. In 1877. In 1815 and 1816 and from 1866 to 1888. From 1852 to 1863. MINERAL STATISTICS. 129 Total yield in period stated. and largest amount raised in one year during that period. Name of Mine, Remarks. Black tin. Copper ore. _ Copper. Tons, Tons, Tons. Morvah Consols 6 • •t ... In 1873. Morvah and 195 >•> ... From 1837 to 1839. Zennor Mines Mount's Bay 50 175 16 From 1882 to 1884. Consols (Breage) Nanturras 12 • ■• ... In 1904 and 1905. New Balles- 50 ... ... From 1889 to 1894. widden New Great 35 ••• ... From 1892 to 1895. Work New Eosewarne 50 1,065 93 Between 1863 and 1875. New Trumpet 10 400 40 Prom 1881 to 1885. Consols New Wheal 3 ... ... In 1862. Vaddon New West 10 ... In 1874. Eosewarne Neptune, Wheal ... 1.3,760 1,400 Prom 1815 to 1823 and in 1838. (Nearly 3,000 tons in 1838.) North ... 60 3 In 1839. Godolphin North Great 10 4 ... In 1860 and 1862, Work North Levant 3,540 199 60 7 Prom 1854 to 1902. North Eose- ... 60 "9 In 1873. warne North Wheal ... 162 9 In 1856. Unity Old Great Work 98 From 1892 to 1895. Old Wheal 40 "2 In 1863 and 1864. Neptune Osborne, Wheal 2 350 30 In 1838 and 1839 and in 1874. Owen Vean and 100 • t» ... From 1883 to 1885. Tregurtha Downs I Owles, Wheal - 8,540 288 340 20 From 1837 to 1839, in 1841, and from 1853 to 1893. Parbola (see 120 ... *.. In 1838 and in 1874 and also Wheal 1875. Jennings) Parknoweth - 42 In 1837 and in 1841. Paul Downs - i 140 "s In 1855. Penberthy Crofts 60 8,700 631 From 1818 to 1824 and in 1881, 1882, and 1883. Pendeen 140 6,860 326 Prom 1858 to 1870. Consols Penzance 10 ,.. ... In 1853 and 1854. Consols Polrose Mine - 305 ... Prom 1875 to 1879. 9361 K 130 GEOLOGT 03? LANDS END. Name of Mine. Total yield in period stated, and largest amount raised in one year during that period. Black tin. Copper ore. Copper. Bemarks. Prosper, "Wheal, etc. (Ludg- van?) ■ Prosper United Prosper and Mitchell United Prospidnick, Wheal Providence, Wheal]' Providence Mines Providence United, Lelant Eeeth, Wheal - Eeeth Consols - Setallack Relistian Consols Rodney, Wheal Rosewall Hill and Bansome United Bosewarne Consols Bosewarne and Herland and Bosewarne United St. Aubyn and Grylls(Qreat Wheal Gry Us) St. Ives Consols St. Ives Wheal Allen St. Just Amal- gamated Tons. Tons. 14,600 5,993 Tons. 956 406 830 191 22,500 4,523 1,020 234 70 ... ... 25 ... ... 4,750 406 15,260 1,314 2,340 353 10,030 768 17 ... ... 1,955 ... ... 888 5 10,020 12,150 940 1,032 1,500 6,850 1,795 426 113 45 172 2,950 697 14,480 2,527 272 73 1,200 218 681 142 890 70 7,000 340 450 45 116 ... • •■ 1,112 ... ... From 1832 to 1835, in 1839 and 1840, and from 1845 to 1849. From 1863 to 1872. From 1863 to 1866. In 1861 and 1862. From 1820 to 1847. Accord- ing to the Mining and Smelting Magasine, 9,700 tons of black tin were raised between 1835 and 1862, 590 tons being largest amount raised in one year. Copper ore between 1836 and 1855. Tin ore be- tween 1852 and 1861. In 1885. In 1837, 1838, and 1839, and from 1853 to 1867. From 1855 to 1860. From 1831 to 1836. Between 1832 and 1842. Tin since 1852. Between 1824 and 1848. From 1859 to 1876, Some in 1839. From 1858 to 1869. From 1854 to 1874. From 1850 to 1862. In 1837, and from 1853 to 1892. Some of the tin in 1838 and 1839. Between 1862 and 1868. From 1868 to 1878 MINERAL STATISTICS. 131 Total yield in period stated, and largest amount raised in one year during that" period; ndAni/^ rxf KrT iv^/^ >_ _ Remarks. j-^ame oi iviine. Black tin. ^°o?r- <^0PPe- Tons. Tons. Tens. St. Just Consols 2 ... ... In 1864 St. Just United 1,870 ,,, • •• From 1862 to 1904. Shepherds 40 ... In 1885. United (Breage) Sisters, Wheal 4,650 600 2,990 235 From 1845 to 1848; 1875 tol900; 3,C06 tons of ore containing 238 tons of copper were produced betjveen 1825 and 1848. Sithney Wheal 18 ... ... In 1858. Buller South Alfred - • • • 3 In 1866. South Carzise 50 ... In 1872. and Maria South Crenver >•• 5,210 192 From 1853 to 1856. South Wheal Fortune South Great ... 770 86 From 1847 to 1850. 100 ... ... From 1872 to 1876. Work South Wheal ... 172 14 In 1842 and 1843. Neptune South Grylls - South Providence ... 18 In 1866. 80 ... From 1855 to 1882. South Speed. - 55 105 5 In 1852 and 1855. South Tindene 1 In 1891. Spearn Consols 565 34 "4 In 1833 and 1834 and from 1853 to 1873. Wheal Spearn between 1819 and 1821 yielded 88 tons of ore containing 9 tons of copper. Spearn Moor - 1,665 62 13 From 1835 to 1837 ; in 1841; 89 and from 1854 to 1878. Speed, Wheal - Speedwell, 4,100 305 Between 1825 and 1843. '"i 11,360 870 Prom 1819 to 1854. Wheal Stennack, Wheal Strawberry, 1 ... ... In 1880. • • . 9,750 575 From 1830 to 1837. Wheal Sydney Cove ... 350 27 In 1838 and 1839. Mine Sydney 91 • •• ... In 1853 and from 1886 Godolphin Tindene - 167 From 1887 to 1892. Tolvaddon 12 10,750 2,442 670 151 From 1857 to 1866. Trannack and 26 485 33 Since 1851. Bosence ^ » n 9564 132 GEOLOGY OP LANDS END. Name of Mine. Total yield in period stated, and largest amount raised in one year during that period. Black tin. Copper ore. Copper. Remarks. Treasure, Wheal Treasury, Wheal Trebarvah Tregembo Tregillia Stream Works Tregurtha Downs (after- wards Helena and now Wheal Hamp- ton) Treloweth Trelyon Consols Tremayne, Wheal Trenerom Trenow Consols Trenwith, Wheal Trevaskus Trevelyan Treven Mine - Trevenna Mine Trevethoe Trewavas Unity Consols, Wheal Verrant, Wheal Violet Seton - Virgin, Whe&l- Tons. 112 46 1,195 190 1,200 87 1,492 191 1,025 20 110 270 72 M 140 Tons. 7,180 Tons. 605 6,790 448 3,450 525 6 244..^ 36 6,490 1,030 100 405 60 9 5,260 1,646 309 85 2 6,765 13,080 2,062 654 1,450 236 1,190 121 15 ■ .. ■ 17,400 1,414 2,830 506 170 32 1,270 7,090 74 845 From 1815 to 1822. From 1826 to 1844. From 1852 to 1874. Prom 1883 to 1888. From 1855 to 1860. From 1886 to 1897. From 1854 to 1866. 1874. Tin from 1853 to Copper in 1851. From 1848 to 1868. From 1848 to 1856, 5,190 tons of ore containing 305 tons of copper were yielded. From 1861 to 1876. From 1844 to 1856. From 1825 to 1856. 10,840 tons of ore containing- 1,170 tons of copper were yielded between 1826 and 1836; in 1838, and from 1845 to 1857. From 1838 to 1842. Tin in 1838 and 1839. From 1852 to 1860. In 1872 and 1873. From 1852 to 1856. In 1903. From 1836 to 1846. From 1851 to 1865. From 1815 to 1856, 851 tons of ore containing 50 tons of copper were raised. In 1905. From 1881 to 1887. From 1838 to 1840. MINERAL STATISTICS. 133 Total yield in period stated, and largest amount raised in one year during that period. Namp nf IVf inp Remarks. XI ullic \Jl vlJ,M.lLKS» Black tin. Copper , ore. Copper. Tons. Tons. Tons. Weeth - ■ •. 4,370 465 From 1815 to 1821. Wellington • *. 5,415 450 From 1823 to 1827, 1847 to Mines and " 1851. "Wheal • .• Wellington West Wheal • •• 4,325 284 From 1815 to 1854. Alfred *•■ 1,957 139 West Alfred ■ •■ 8,400 347 From 1852 to 1865. Consols >•■ 1,188 48 West Bostraze- 18 >■• ... In 1889 and 1890. West Carzise - 4 ... ... In 1888 and 1889. West Ding 20 ... In 1853 and 1855. Dong Mine West Wheal ... 6,220 585 From 1815 to 1828. Fortune West Godolphin 1,510 210 36 From 1870 to 1890. West Great 462 177 14 From 1863 to 1876. Work West Grylls - 3 30 2 In 1862, 1864, and 1865. West Wheal 1 ... In 1873. Lucy- West Wheal • .* 9 • *> In 1878 and 1879. Mary West Wheal 7 IC In 1865 and 1866. Prosper West Provi- 790 1,535 163 From 1851 to 1862, 1881 to dence (Buzza) 1883. West Hoskear - 10 500 26 From 1874 to 1880. WestTolvaddon ■ •• 40 2 In 1862 and 1863. West Wheal *•. 9,500 724 From 1845 to 1854. Treasury 1,595 125 WestTremajne • >. 70 4 In 1868 and 1869. West Wheal 2 980 83 From 1859 to 1864. Trevelyan Wherry Mine - some ... ... In 1859. JE70,000 worth of tin ore raised before 1 818. Widden, Wheal 183 ... ... In 1859 and 1860. Worvas Downs 48 ... ... From 1862 to 1864, and in 1905. Yankee Boy - 15 ... ... In 1896. Output of Minerals other than Tin and Copper Ores. The amounts yielded by the mines of the region other than ores of tin and copper are estimated from details published in official records since 1854. ThSy cannot be considered as complete, but they afford a good general guide to' the relative importance of the minerals wrought, and of their quantitative distribution. 134 GEOLOGY OF LAND S END. Ontde and Botallaok Florence Consols Great Wheal Fortune Great Western Mine Great Work Mine Leedstown Consols . . . Levant... North. Rosewarne New West Rosewarne North Levant Wheal Owles Befitted Arsenic and Arsenical Pyrites. Tons. ... 1,525 Prosper United 10 Relistian Consols 1 90 Eosewall Hill and Ransome 50 St. Aubyn and Grylls 2 Spearn Moor... 12 Sydney Godolphin ... 3,865 T-indene 80 Tregembo 16 Tregnrtha Downs 2 Wheal Unity Consols 50 West Wheal Mary . Boiling Well Emily, Wheal Lead Ore and Lead. Lead Ore. Lead. Tons. Tons. ... 410 ... 303* 75 ... 55 Great Wheal Alfred, a few owt.j Millet, Wheal ... Si ... 4 Penberthy Crofts... ij ... , i Prosper United ... 60 ... 36 J Tolvaddon 3 ... 2 Treven Mine Trungle, Wheal ... Venton, Whea.1 Violet Seton West Alfred Consols Lead Ore. Tons. 1 .. U .. .. 4i .. .. 56 ., 3i . Tons. 1,165 5 12 15 8 15 12 5 32 144 5 Lead. Tons. West Rosewarne, a few cwt. West Roskear ... 48 ., Zinc Ore (Blende). Tons. Arthur, Wheal 160 Alfred, Wheal, and Alfred Consols 245 Boiling Well 54 Carpenter, Wheal 80 East Alfred Consols 25 Emily, Wheal 25 Gill, Wheal 200 to 300§ Mellanear Rosewarne and Herland Tolvaddon Trungle, Wheal Violet Seton ... West Alfred Consols. West Wheal Mary West Roskear... 36 2 35 Tons. 1,400 110 8 45 212 30 7 350 Iron Ore and Ochre. Binner Downs Castle, Wheal Trebarvah At Hawkes Point a ton of ochre was obtained. Brown Hsematite. 100 tons. 75 „ .. 1,730 „ East Alfred Consols Margery," Wheal . . . Mellanear Iron Pyrites. Tons. 92 35 12 Prosper United Treven West Rosewarne Tons. . 200 3 .. 14 Miscellaneous Ores. From East Rosewarne about £250 worth of arsenical silver ore was sold in 1858 and 1859. Silver ore obtained since 1854 from Her]and|| and Rosewarne (106 ozs.) ; West Roskear (105 ozs.) ; Wheal Trungle ; West Alfred Consols (28 ozs.) ; West Dolcoath and from Wheal Trebarvah in 1903 (21,000 ozs.). In 1905, 3,440 ozs. of silver were obtained from 14 tons of silver ore at the Perran Mine near Marazion. Silver has also been obtained by liquation from lead ores. Between 1852 and 1853, 351 tons of silver ore, realising £3,700, were sold. * Nearly 5,000 ozs. of silver obtained. j Before 1814 very many tons of galena and lead carbonate were sold from this mine. t Nearly 200 ozs. of silver obtained. . § Between A.D. 1820 and 1830. Pryce, Min. Corn., 1788. II Between £8,000 and £9,000 worth of silver ore was sold from the Herland Mine before 1814." - - . - INDEX OF MINES. ISS In, 1878 and 1879 about 5 cwt. of pitchblende and other uraninm oies with bismuth were raised from Wheal Owles. This mineral has been found in the St. Ives and other districts. In the Providence Mines (St. Ives) 3 tons of uranium ore were raised before 1846, wlule several hundred- weight have been raised since. Some tons of cobalt ore were raised from the Wherry Mine. Index of Mines Alphabetically Arranged, MiNB. Alfred, Wheal Alfred Consols Anna, Wheal Annie, Wheal A^us, Wheal Augusta, Wheal - Avrack and Nan- cothan Ayr, Wheal - Badger Shaft Bal, Wheal - Balleswidden Ballowall Baln'oon Consols - Balwest Bellan Mine - Billia - Binner Consols Binner Downs Bodraverran Boiling Well Mine Bolton, Wheal Bosoaswell Downs Boscaswell United Boscean Mine Bosorne and Ballowall - Bostraze Botallack Bounds and Bellan Boswase Boswarlas Mine - Boswartha Mine - Boswedden Mine - Bowling Green Boys, Wheal - Breage Mine Buck, Wheal - Bull, Wheal - Burnt Downs Button, Wheal Caer Bran Mine - Call, Wheal - Calloose Cape Cornwall Mine Cam, Wheal - Carnelloe Mine Carn Galver Mine Camleskis Carnyorth Pasish. Phillack Phillack St. Hilary Gwinear Sancreed St. Just Sancreed St, Ives St, Just St. Just St. Just St. Just Uny Lelant Germoe St. Just Towednack Crowan Crowan St, Erth Phillack Ludgvan St, Just St, Just St, Just St. Just St, Just St. Just St, Just Ludgvan St, Just Sancreed St, Just Gwinear St, Just Breage St, Just St, Just Crowan St. Just Sancreed St. Just Gwinear St. Just St. Just Zennor Zennor St, Just St. Just Mine, Caroline, Wheal - Carpenter, Wheal - Carrick Du Mine - Carzise Mine Castle, Wheal Charlotte, Wheal Cherry, Wheal Collarian Mine Cock, Wheal Croft an Vor Croft Gothal Mine Crowan Consols - Crowns Mine Cubert, Wheal Cunning, Wheal Darlington, Wheal Davy's Shaft Diamond, Wheal Ding Dong - Drannack Drea, Wheal - Drewollas Dumpling, Wheal - Durlo Bast Boscaswell - East Great Work - East Wheal Grylls East Levant ■ East Wheal Mar- garet - - - Bast Wheal Nep- tune - East Providence - East Wheal Reeth Bast St, Just United Bast Tregembo East Trevelyan Edward, Wheal - Emily, Wheal Bnys Wheal Virgin Fancy, Wheal Florence, Wheal - Fraddam Friendship, Wheal Fristan, Wheal Parish. Perranuthnoe Gwinear St. Ives Crowan St. Just Perranuthnoe Uny Lelaut Uny Lelant St. Just St. Just St. Hilary Crowan St. Just Uny Lelant St. Just Ludgvan St. Just St. Just Madron Gwinear St. Just Gwinear Crowan Towednack St. Just Breage Breage St. Just Uny Lelant Perranuthnoe St. Ives Uny Lelant St. Just Crowan Perranuthnoe St. Just Gwithian f St. Erth \ St. Hilary St. Hilary /St. Hilary l Perranuthnoe Gwinear St. Hilary Morvah 186 GEOLOGY OF LAND S END. Mine. Geevor, Wheal Georgia Mine Georgia, Wheal - Gilbert, Wheal - Gilmar Mine Gill, Wheal Godolphin Goldings Mine Goole Pellas Goth, Wheal - Great Wheal Grylls Great North Setou Great Trevegean Mine - - - Great Western Mine - - - Great Work Mine- Giey, Wheal Grous, Wheal Grouse Tin Mine Grylls, Wheal Gurlyn Mine- Gurnards Head Guskas Mine Gwallon Mine Gwin and Singer - Halamanning Hampton, Wheal - Hartley, Wheal Hawk, Wheal Hawkea Point Mine Hearle, Wheal Helena, Wheal Hen, Wheal - Hendra Mine Herland Mine Hermon Hill - Hobboys Mine Hopes, Wheal Hor, Wheal - Jennings, Wheal - Julia - - - Jewell, Wheal Kayle, Wheal Kelynack Kidney, Wheal - - Kitty, Wheal- Lambo - - - Lamin Mine - Land, Wheal - Lang, Wheal - Leeds^ Wheal Leeds and St. Aubyn - - - Pajhsh. St. Just Towednaok / Breage \ St. Hilary St. Erth St. Erth St. Ives Breage St. Just r St. Ives \ Uny Lelant Morvah Breage Camborne St. Just / Breage \ Germoe Breage Germoe Morvah St. Just f St. Hilary \ Breage ' St. Erth Zennor St. Hilary / Ludgvan \ St. Hilary Breage St. Hilary St. Hilary Gwinear r St. Ives \ Uny Lelant Uny Lelant St. Just St. Hilary St. Just Breage Gwinear St. Just St. Just Gwinear St. Ives Gwinear ■ Crowan Marazion Phillack St. Just St. Erth Uny Lelant Gwinear Gwinear St. Erth Morvah / Breage 1 St. Hilary / St. Hilary \ Germoe Mine. Lelant Consols Letcha Levant - - - Lewis Mine - Little Bounds Liverpool, Wheal - Locke, Wheal LogganS or Phil- lack Towans London, Wheal Lucy, Wheal - Maggot, Wheal Maitland, Wheal - Marazion Mines - Margaret, Wheal - Margery, Wheal - Mary, Wheal - Mellanear Mine Mellanoweth - Merth, Wheal Millet, Wheal Millpool Mine Molesworth, Wheal Morvah Consols - Morvah Hill Mine Mounts Bay Con- sols - - - Nanterrow - Nanturras Nelson, Wlieal Neptune, Wheal - Noble Dale - North Hearle North Levant Mine North Rosewarne - North Wheal Unity Old Tincroft Mine Osborne, Wheal - Owen Vean - Owl, Wheal - Owles, Wheal Parbola - - - Parknoweth - Paul Downs - Penberthy Crofts - Pendarves and St. Aubyn Pendeen Mine Perran Mine- Plain an Gwarry - Polkinghorne Polpeor ... Polrose Mine Powle, Wheal Praed Consols Praze, Wheal Pabish. Uny Lelant St. Just St. Just St. Erth St. Just Gwithian St. Ives Phillack St. Just Phillack Phillack St. Just Marazion {Ludgvan Uny Lelant St. Ives r St. Ives i Sancreed (.Uny Lelant St. Erth Phillack Uny Lelant Crowan / Breage \ St. Hilary Camborne Morvah Morvah Marazion Gwithian St. Hilary Crowan Perranuthnoe St. Hilary. St. Just St. Just Gwinear Gwinear Sancreed' Crowan / Perranuthnoe \St. Hilary St. Just St. Just Gwinear St. Just Crowan St. Hilary Gwinear St. Just Perranuthnoe St. Hilary Gwinear Uny Lelant Breage Sfc. Just Uny Lelant St. Jinst INDEX OF MtNES. 137 Mine. Prince George Mine Prosper, Wheal - Providence, Wheal Providence, Wheal Eeath, Wheal Eeeth, Wheal Reeth Consols Relistian Consols - Retallaok Riblose - Rodney, M'heal Rome, Wheal Rose, Wheal - Eosewall Hill and Ransome United Rosewarne and Her- land - - - Rospeath St. Aubyn and Grylls St. Ives Wheal Allen - St. Ives Consols - St. Just Amalgam- ated - - . Sisters, Wheal So,uth Crenver South Great Work South Wheal Mar- garet - South Wheal Nep- tune - - . South Providence - South Wheal Rose South Wheal Speed Spear n Consols Spearn Moor Speed, Wheal Speed, Wheal Speedwell Mine - Stennack, Wheal - Strawberry, Wheal Strawberry, Wheal Sydney Cove Mine Sydney Godolphin- Tindene Tolvean Trannaok, Wheal - Travarraok Mine - Treasury, Wheal - Trebarvah Treen Mine - Tregembo Tregurtha Tregnrtha Downs - Treloweth Trelyon Consols - Tl^elyon Downs Pabish. Gwinear f St. Hilary \ Ludgvan Uny Lelant Gwinear Uny Lelant Germoe Towednaok Gwinear St. Hilary St. Just St. Hilary Camborne Zennor f Lelant \ Towednack Gwinear Ludgvan Breage St. Ives r St. Ives \ Towednack St. Jitst Uny Lelant Crowan St. Hilary Uny Lelant Perranuthnoe Towednack St. Just Uny Lelant St. Just St. Just Breage St. Ives Breage St. Just Uny Lelant Crowan Breage Breage Breage St. Just St. Erth Uny Lelant / Crowan \ Gwinear Perranuthnoe Zennor St. Hilary St. Hilary St. Hilary St. Erth / St. Ives \ Uny Lelant St. Ives Mink. Tremayne, Wheal - Trembethow - Tremellin Trehcrom Trenow - Trenowyn Trenwheal Trenwith, Wheal - Trerice - Trescowe Tye Mine Trevan Mine Trevarthian Mine- Trevean Mine Trevethoe Trewavas Trewidden Bal Tolvaddon - Trungle, Wheal - Truthall Truthwall Mine - Truthwall Mine - Tyringham Consols Unity, Wheal Unity, Wheal Unity Consols Venton, Wheal Verrant, Wheal Violet Seton Virgin, Wheal Vyvian Consols Wellington, Wheal West Wheal Abra- ham - - - West Alfred Con- sols - - - West Wheal Alfred West Carzise- West Wheal Dar- lington - ^. West Godolphin - West Great Work West Wheal Lucy - West Wheal Owles West Poldice West Providence - West Roskear West Tolvaddon West Wheal Trea- sury - West Trevelyan - Wherry Mine Widden, Wheal William, Wheal - Winze, Wheal Worvas Downs Yankee Boy - Zennor Head Mine Zendra, Wheal Pabish. Gwinear Uny Lelant St. Erth Uny Lelant Perranuthnoe Penzance Breage St. Ives Sanoreed / Breage \ Germoe St. Erth St. HUary Perranuthnoe Uny Lelant Breage Madron Marazion Gwinear Ludgvan Crowan St. Just Towednack Gwinear St. Just Gwinear St. Just St. Hilary Camborne / Ludgvan \ Marazion Gwinear St. Hilary Crowan f Phillack \ St. Erth St. Erth Crowan Ludgvan Breage Uny Lelant St. Just Uny Lelant St. Erth Camborne Paul Crowan Perranuthnoe Penzance f St. Just \ Morvah St. Just Towednaok Uny Lelant St. Just Zennor St. Just 138 GEOLOGY OF LAND S END. List of Mines grouped according .to the parishes in which they are situated. The following index gives the positions of the mines on this sheet. The Boman numerals indicate the numbers of the 6-inch-and 25-inch maps issued by the Ordnance Survey. The letters indicate the quarter sheets of the 6-inch maps, while the figures represent the numbers by which the 25-inch maps are designated. Thus, Godolphin Mine LXIX., S.E. 15, means that Godolphin is situated on the 6-inch Ordnance map LXIX. in the S.E. quarter sheet ; while on the 25-inch map it is situated on sheet LXIX. in map No. 15. B RE AGE, Pariih of. Breage Mine, see Gwin and Singer. Bast Great Work, LXIX., S.E. 16. East Wheal Grylls, see Great Wes- tern Mine. Godolphin Mine, LXIX., S.E. 15. Georgia, Wheal, LXXV., N.W. 5. Great Western Mine, LXXV., N.W. 6. (Formerly Wheal Grylls, East Wheal Grylls, Great Wheal Grylls, Grylls Wheal Florence, and West Wheal Grylls.) Great Work Mine, LXXV., N.E. 3. Great Wheal Grylls, see St. Aubyn and Grylls. Great Work Mine, LXXV., N.E. 3. Grylls, Wheal, LXXV., N.W. 6. Gwin and Singer. Hendra Mine, LXXV., N.E. 7. Leads, Wheal, LXXV., N.W. 2. Leeds and St. Aubyn, LXXV., N.W. 6. Millpool Mine, LXXV., N.W. 2, Polrose Mine, LXXV., N.E. 4. Prosper, Wheal, LXXV., S.E. 11. St. Aubyn and Grylls, LXXV., N.W. 6. Sydney Cove Mine, LXXV., N.W. 6. Sydney Godolphin, LXXV., N.W. 6. Speed, Wheal, LXXV., N.W. 6. Speedwell Mine, LXXV., N.W. 5. Tindene Mine, LXIX., S.W. 14. Trenvrheal, LXIX., S.E. 12. Trewavas, LXXV., S.E. 11. Trescowe Tye Mine, LXXV., N.E. 3. West Godolphin Mine, LXIX., S.W. 14. West Great^Work, LXXV., -N.W. 2. CROWAN, Parish of. Binner Downs Mine, LXIX., S.E. 12. Binner Consols, LXIX.^S.E. 11. Burnt Downs, LXIX., S.E. 11. Carzise Mine, LXIX., S.E. 11. Crowan Consols, see Wheal Dump- ling. Dumpling, Wheal, LXIX.; S.E. 12. East Tregembo, see Wheal Osborne. Julia, Wheal, see Wheal Strawberry. Millet, Wheal, LXIX., S.E. 16. Nelson, Wheal, LXIII., S.W. 13. Osborne, Wheal, LXIX., S.E. 15. Paul Downs Mine, LXIX., S.E. 11. South Crenver. Strawberry, Wheal, LXIX., S.E. 12. Treasury, Wheal, LXIX., S.W. 7. Truthwall Mine, LXIX., N.E. 7. West Wheal Abraham, LXIX., S.B. 11. West Wheal Treasury, LXIX., S.W. 9. West Carzise, LXIX., S.E. 11. OERMOE, Parish oj. Balwest, LXXV., N.E. 3. Great Western Mine, LXXV., N.W. 6. Grey, Wheal, LXXV., N.E. 7. Great Work Mine, LXXV., N.E. 3. Leeds and St. Aubyn, LXXV., N.W. 6. Beeth, Wheal, LXXV., N.E. 3. Trescowe Tye Mine,- LXXV., N.E. 3. CAMBORNE, Parish pf. Great North Seton, LXIL, N.E. 8. Molesworth Wheal, LXIL, S.E. 16. Eome, Wheal, see West Roskear. Violet Seton, LXIL, N.E. 8. West Roskear, LXIL, S.E. 12. OULVAL, Parish of. Carnaquidden Mine, LXVJU., N.W. 6. Ding Dong Mine, LXVII., S.E. 12. INDEX OF MINES. 139 GWINEAR, Parish of. Annie, Wheal, LXIL, S.B. 16. Bowling Green, LXIX,, N.E. 3. Calloose, LXIX., N.E. 7. Carpenter, Wlieal, LXIX., N.E. 7. Drannack, LXIX., N.E. 3. Drewollas, LXIX., N.E. 8. Fraddam, LXIX., N.E. 7. Herland,. Wheal, LXIX., N.E. 3, Hopes, Wheal, LXIX., N.E. 7. Hartley, Wheal, LXII., S.E. 16. Jennings, Wheal, LXIX., N.E. 4. Lamin Mine, LXIX., N.E. 3. Lambo (part of Wheal Tremayne), LXIX., N.E, 7. North Eosewarne Mine, LXIX., N.B. 3. North Wheal Unity, LXIX., N.E. 7. Parbola, see Wheal Jennings. Pendarves and St. Aubyn Consols, LXIL, S.B. 16. Polkinghorne Mine, LXIL, S.E. 15. Prince George Mine, see Herland. Providence, Wheal, LXIX., N.W. 6. Eelistian Consols, LXIX., N.E. 3. Eosewarne and Herland United, LXIX., N.E. 3. Tremayne, Wheal, LXIX., N.E. 7. Trevaskus, Wheal, LXIL, S.E. 15. Trungle, Wheal, LXIX., N.E. 1. Treasury, Wheal, LXIX., N.E. 7. Unity, Wheal, LXIX., N.E. 8. Unity Consols, Wheal, LXIX., S.W. 9. Vyvian Consols, LXIX., N.E. 3. OWITEIAN, Pariah of . tJmily, Wheal, LXII., N.W, 6. Liverpool, Wheal, LXIL, S.W. 10. Nanterrow, LXIL, N.E. 7. LUDGYAN, Parish of. Bolton, Wheal. Boswase, LXVIIL, N.B..7. Darlington, Wheal, LXVIIL, S.E. 15. Gwallon Mine, LXVIIL, S.E. 16. Margaret, Wheal. Prosper, Wheal, LXVIIL, S.B. 16. Eospeath, LXVIII„.S.B. 16. Truthall, LXVIIL, S.E. 16. Virgin, Wheal, LXXIV., N.B. 4. West Wheal DarliBgton, LXXIV., N.E. 3. MADRON, Parish of. Ding Dong Mine, LXVII., S.E. 12. Trewidden Bal, LXXIV., N.W. 5. MARAZION, Pa/rish of. Jewell, Wheal, LXXIV., N.B. 4. Marazion Mines, see Wheal Virgin. Mounts Bay Consols, LXXIV., N.B. 4. Tolvaddon, LXXIV., N.B. 4. Virgin, Wheal, LXXIV., N.E. 4. MORVAH, Parish of. Fristan, Wheal, LXVII., NJE. 7. Goth, Wheal, LXVII., N.B. 7. Grous, Wheal, LXVII., N.E. 7. Lang, Wheal, LXVIL, N.B. 7. Morvah Consols, LXVIL, N.B. 7. Morvah Hill Mine, LXVIL, N.B. 7. Morvah and Zennor United, LXVIL, N.B. 7. (See Frisian, Goth, Grous, Lang, and Widden.) Widden, Wheal, LXVIL, N.B. 7. PAUL, Parish of. West Tolvaddon, LXXIV., S.W. 10. PENZANCE, Parish of. Trenowyn, Chellew, and Menwid- dian. Wherry Mine, LXXIV., N.W. 6. PERRANUTHNOE, Parish of. Caroline, Wheal, LXXV., N.W. 1. Charlotte, Wheal, LXXV., N.W. 5. East Trevelyan Mine, LXXV., N.W. 1. East Wheal Neptune, LXXV., N.W. 1. Florence, Wheal, LXXV., N.W. 5. Neptune, Wheal, LXXV., N.W. 1. Owen Vean Mine, LXXV., N.W. 1. Perran Mine, LXXV., N.W. 5. South Wheal Neptune, LXXV., N.W. 5. Trebarvah, Wheal, LXXV., N.W. 5. (Part of Mount's Bay Consols.) Trenow, LXXIV., N.E. 8.. Trevean Mine, LXXV., N.W. 5. West Trevelyan Mine, LXXV., N.W. 1. 140 GEOLOGY OF LAND S END. PHILLAGK, Parish of. Alfred, Wheal, LXIX., N.W. 2. Alfred Consols Mine, LXIX., N.W. 2. Boiling Well Mine, LXII., S.W. 10. Kayle, Wheal. Loggans or Phillack Towan, LXII., S.W. 14. Lucy, Wheal, LXII., S.W. 13. Maggot, Wheal, see Mellanoweth. Mellanoweth, LXII., S.B. 15. Prospect, Wheal, LXIX., N.W. 2, West Alfred Consols, LXIX., N.W. 2. ST. ERTH, Parish of. Bodraverran, LXIX., N.W. 6. Enys Wheal Virgin, LXIX., S.W* 14. Gilbert, Wheal, LXIX., S.W. 14. Gilmar Mine (Gear), LXIX., S.W. 10. Gurlyn Mine, LXIX., S.W. 14. Kidney, Wheal, LXIX., S.W. 14. Land, Wheal, see West Alfred Con- sols. Lewis Mine, LXIX., S.W. 10. Mellanear Mine, LXIX., N.W. 5. Treloweth, LXIX., N.W. 5. Tremellin Mine, LXIX., S.W. 9. Treven Mine, LXIX., S.W. 10. Trannack, LXIX., S.W. 10. West Alfred Consols, LXIX., S.W. 2. (Part of Mellanear.) West Wheal Alfred, LXIX., N.W. 5. West Providence, LXIX., N.W. 6. ST. HILARY, Parish of. Anna, Wheal (near Guskas), LXIX., S.W. 14. Croft Gothal Mine, LXXV., N.W. 2. Enys Wheal Virgin, LXIX., S.W. 14. Fancy, Wheal, LXIX., S.W. 14. Florence, Wheal, LXXV., N.W. 5. Friendship, Wheal, LXIX., S.W. 13. Georgia, Wheal, LXXV., N.W. 5. Grylls, Wheal, LXXV., N.W. 6. Guskas Mine, LXIX., S.W. 14. Gwallon Mine, LXVIII., S.E. 16. Halamanning, LXXV., N.W. 2. Hampton, Wheal, see Tregurtha Downs. Helena, Wheal, see Tregurtha Downs. Leads, Wheal, LXXV., N.W. 2. Leeds and St. Aubyn, LXXV., N.E. 6. Millpool Mine, LXXV., N.W. 2. Nanturras Mine, LXXV., N.W. 1. Noble Dale (or New Wheal Vaddon and New Grylls), east of Wheal Neptune. Owen Vean Mine, LXXV., N.W. 1. Penberthy Crofts, LXIX., S.W. 13. Plain an Gwarry, LXVIII., S.E. 16. Prosper, Wheal, LXIX., S.W. 13. Eetallack, LXXV., N.W. 2. Rodney, Wheal, LXXV., N.E. 4. South Great Work, LXXV., N.W. 2. Tregembo, near Halamanning. Tregnrtha Downs, LXXV, N.W. 1. Tregurtha, LXVIII., S.E. 16. Trevarthian Mine, LXIX., S.W. 14. Wheal Verrant. Wellington. Wheal, see Wheal Grylls. ST. IVES, Parish of. Ayr, Wheal, LXI., S.B. 11. Carrick Du Mine, LXI., S.E. 11. East Providence, east of Wheal Providence. Gill, Wheal. Goole Pellas, LXI., S.E. 11. Hawk, Wheal, see Providence Mine. Hor, Wheal, LXL, S.E. 11. Looke, Wheal. Margery, Wheal, LXI., S.E. 16. Mary, Wheal, LXL, S.E. 11. St. Ives Wheal Allen, LXL, S.E. 11. St. Ives Consols, LXL, S.E. 11. Speed, Wheal, south of Wheal Pro- vidence. Trelyon Consols, LXL, S.E. 11. Trelyon Downs, LXL, S.B. 16. Trenwith, Wheal, LXL, S.E. 11. ST. JUST, Parish of. Augusta Mine, west of Balles- widden Badger Shaft, LXXIIL, N.W. 1. Bal, Wheal, LXVIL, S.W. 10. Balleswidden, LXXIIL, N.W. 2. Ballowall (see Bosorne), LXXIIL, N.W. 1. Bellan Mine, LXXIIL, N.W. 1. Boscaswell Downs, LXVIL, S.W. 10. Boscaswell United, west of Boscas- ' well Downs. Boscean Mine, LXXIIL, N.W. 1. Bosorne Mine and Ballowall. LXXIIL, N.W. 1. Bostraze. Boswarlas Mine, LXXIIL, N.W. 6. Boswedden Mine (see Wheal Castle). LXVn., 8.W. 13. '' INDEX TO MINES. 141 Botallack (and Truthwall), LXVII., S.W. 13. Bounds and Bellan Mine (part of St. Just Amalgamated), LXXUI., N.W, 1. Boys, Wheal, LXVII., S.W. 14. Buck, Wheal, near Wheal Bellan. Ball, Wheal, LXXIII., fJ.W. 6. Button, Wheal, part of Botallack. Call, Wheal, LXVII., S.W. 13. Cape Cornwall Mine, LXXIII., ■ N.W.I. Carn, Wheal, LXVII., S.W. 10. Carnleskis, see South Wheal Bose. Carnyorth, LXVII., S.W. 14. Castle, Wheal, LXVII., S.W. 13. Cock, Wheal, LXVIL, S.W. 9. Croft an Vor, south of Balleswidden. Crowns Mine, LXVlL, S.W. 13. Cunning, Wheal, LXXIII., N.W. 1, Davy's Shaft, LXXIII., N.W. 2. Diamond, Wheal, LXXIII., N.W. 5. Drea, Wheal, LXVII., S.W. 13. Bast Boscaswell, LXVIL, S.W. 10. East Levant Mine, LXVII., S.W. 10. Bast St. Just United, see Bosorne and Ballowall. Edward, Wheal, LXVIL, S.W. 13. Geevor, Wheal, see North Levant. Goldings Mine, LXXIII., N.W. 1. Great Trevegean Mine, LXXIII., N.W. 5. Grouse Tin Mine, LXXIII., N.W. 1. Hearle, Wheal. Hen, Wheal, near Wheal Cock. Harmon Hill, LXXIIL, N.W. 1. Hobboys Mine, LXXIIL, N.W. 2. Kelynack, LXXIII., N.W. 6. Letcha, LXXIIL, N.W. 5. Levant Mine, LXVIL, S.W. 10. Little Bounds, LXIIL, N.W. 1. London, Wheal, see Boscaswell. Maitland, Wheal, formerly Wheal Carne, Wheal London, etc. North Hearle, south-east of Fendeen Consols. North Levant Mine, LXVIL, S.W. 10. Owl, Wheal, part of St. Just Amal- gamated. Owles, Wheal, LXVIL, S.W. 13. Parknoweth, between Botallack and Wheal Owles. Pendeen Mine, LXVIL, N.W. 6. Powle, Wheal, LXVIL, S.W. 10. Praze, Wheal, LXVIL, S.W. 13. Eiblose, LXXIIL, N.W. 1. St. Just, Wheal, LXIIL, N.W. 1. St. Just Amalgamated, LXXIIL, N.W. 1. South Wheal Rose, LXXIIL, N.W. 1. Spearn Consols, LXVIL, S.W. 10. Spearn Moor Mine, LXVIL, S.W. 9. Stennack, Wheal, see Boscaswell and East Levant. Tolvaen, part of Wheal Cock, Truthwall, see Botallack. Unity, Wheal, LXVIL, S.W. 10. VentoD, Wheal, LXXIII,, N.W. 1. West Wheal Owles, LXVIL, S.W. 13. Widden, Wheal, LXXIIL, N.W. 1. William, Wheal, near Wheal Castle. Yankee Boy, LXVH., S.W. 13. ■Zendra, Wheal (part of B,oscaswell Downs), LXVIL, S.W. 10. SANGREED, Parish of. Argus, Wheal, LXXIIL, N.E. 8. Avrack and Naneothan Mine, LXXrV., N.W. 5. Boswartha Mine, LXXIIL, N.B. 7. Caer Bran Mine, LXXIIL, N.E. 7. Treriee, LXXIIL, N.E. 8. TOWEDNAGK, Parish of. Ayr, Wheal, LXI., S.B. 11. Billia (or Durlo), see Eeeth Consols. Brea Consolidated, LXI., S.W. 10. Georgia Mine, LXVIIL, N.W. 6. Mary, Wheal, LXL, S.B. 11. Old Tincroft Mine, LXVIIL, N.B. 7. Eeeth Consols, LXVIIL, N.E. 3. Eosewall Hill and Eansome United, LXL, S.B. 15. St. Ives Consols, LXL, S.E. 11. South Providence, LXVIIL, N.B. 3. Tyringham Consols, LXL, S.B. 15. Winze,, Wheal, LXL, S.B. 15, VNY LELANT, Parish of. Balnoon Consols, LXL, S.B; 15. Cherry, Wheal, LXVIIL, N.B. 8. Cubert, Wheal, LXVIIL, N.B. 4. Collurian Mine, LXVIIL, N.B. 8. East Wheal Margaret, LXVIIL, N.B, 8. East Wheal Eeeth. Goole Pellas, see Eosewall Hill and Eansome. Hawk, Wheal, LXL, S.B. 16. Hawkes Point Mine, LXL, S.B. 16, Kitty, Wheal, LXVIIL, N.E. 7. Lelant Consols, LXVIIL, N.B. 7. Margaret, Wheal, LXVIIL, N.B. 7. Mary, Wheal, LXVIIL, N.B. 7. Merth, Wheal, LXVIIL, N.E. 8. Polpeor, see Wheal Kitty. Praed Consols, see Wheal Cherry, providence Mine, LXI., S.B, 10. 142 GEOLOGY OF LAND S END. Eeath, Wheal, LXVIII., N.B. 3. Eosewall Hill and Bansome United, LXL, S.E. 15. Sisters, Wheal (or Wheal Reath. Formerly Polpeor or Wheal Kitty, and includes also Wheal Mary, Margaret, and Trenerom), LXVIII., N.B. 7. South Wheal Margaret, LXVIII., N.E. 7. South Wheal Speed, LXI., S.B. 16. Strawberry, Wheal, LXVIIL, N.B. 8. Trenerom, LXVIII., N.B. 4. Trelyon Consols, LXI., S.B. 11, Trembethow, see Lelant Consols. Travarrack Mine, LXVTII., N.B. 4. Trevethoe Limited, LXVIII., N.B. 8, West Poldice, see East Wheal Mar- garet. West Wheal Lucy, LXIL, S.W. 13. Worvas Downs, part of Balnoon. ZENNOR, Parish of. Carnelloe Mine, LXL, S.W. 13. Cam Galver Mine (or Morvah and Zennor Mine), LXVIL, N.E. 8. Gurnards Head Mine, LXVIL, N.E. 4. Rose, Wheal, see Carn Galver. Treen Mine, see Gurnards Head Mine. Zennor Head Mine, LXL, S.W.{13, 143 APPENDIX II. IjISt of Principal Wokks on thjs Gteology of the District. 1602. Cakew, R.— Survey of Cornwall, 4to. (Reprinted in 1769 ) 1671. Anon. — Some Observations on the Mines of Cornwall and Devon, Phil. Trans., No. 69 ; and Phil. Trans, abridged, vol. i., p. 565. 1675. Anon. — The Improvement of Cornwall by Sea Sand. Phil. Trans., vol. X., p. 293. 1757. BoBLASE, Rev. W. — An Aocounb of some Trees discovered under- ground on the Shore at Mount's Bay in Cornwall. Ibid., vol. 1., p. 51. 1758. BoBLASE, Rev. W.— The Natural History of Cornwall. Folio. Oxford. 1778. Pbycb, W. — Mineralogia Gornubiensis. Folio. London. 1781. Jabs, M. G. — Voyages M^tallurgiques. 4to Paris. [Tome iii., p. 186.] -1799. Tatloe, J, — Sketch of the History of Mining in Devon and Corn- wall, Phil. Mag., vol. v., p. 357. 1801. HiTcmiNS, Rev. M. — Account of the Discovery of Silver in Herland Copper Mine. Phil. Trans., vol. xci., p. 159. 1802. Playfaib, Prof. J. — Illustrations of the Huttoniau Theory of the Earth. 8vo. [Granite Veins of St. Michael's Mount, p. 317.] 1814. Phillips, W.— On the veins of Cortiwall. Trans. Geol, 8oe., vol. ii., p. 110. [Herland Mine and Wheal Alfred.] 1818. Caenb, Joseph. — On Elvan Courses. Trans. Boy. Geol, Soc. Corn., vol. i., p. 97. Cakne, Joseph. — On the Discovery of Silver in the Mines of Corn- wall. Ibid., p. 118. Davy, John. — An Account of some Granite Veins at Forth Just, near Cape Cornwall. Ibid., p. 21. Davy, Sir Humphry. — Hints on the Geology of Cornwall. Ibid., p. 38. Hawkins, John. — On Submarine Mines. Ibid., p. 125. [Wherry Mine, p. 131, and PI. i.] Majendie, a. — Notes on the Coast, west of Penzance, and on the Structure of the Scilly Islands. Ibid., p. 27. Paris, J. A. — On a recent Formation of Sandstone, occurring in various Parts of the Northern Coasts of Cornwall. Ibid., p. 1. 1821. Sedgwick, Rev. A. — On the Physical Structure of those Formations which are immediately associated with the Primitive Ridge of Devonshire and Cornwall. Trans. Oamb. Phil. Soe., vol. i., p. 89. 1822. BoASE, H. S.— Observations on the Submersion of part of the Mount's Bay ; and on the Inundation of Marine Sand on the north coast of Cornwall. Trans. Boy. Geol, Soc. Com., vol. ii., p. 129. BoASE, Dr. H. S. — On the Tin-ore of Botallack and Levant. Ibid,, p. 383. Cabne, J. — On the Mineral Productions and the Geology of the Parish of St. Just. Ibid., p. 290. On the Relative Age of the Veins of Cornwall. Ibid., p. 49. FoBBES, Dr. John. — On the Geology of the Land's End District. Ibid., p. 242. On the Geology of St. Michael's Mount. Ibid., p. 366. Hawkins, J. — On the stratified deposits of Tin-stone, called Tin- floors, and on the diSusioi^ of Tin-stone throughout the mass of some primitive rocks. Ibid,, p. 29, 144 GEOLOGY OF LAND's END. 1823. MoTLE, M. P.— On Granite Veins. Ann. Philosophy, n. a., voi. \i. p. 90. [Bast of Trewavas Head.] 1828. Babham, T. p.— Some Arguments in support of the opinion that the Iktis of Diodorus Siculus is St. Michael's Mount. Trans. Boy. Geol. Sac. Corn., vol. iii., p. 86. BoASK, Dr. H. S.— On the Sand Banks of the Northern Shores of Mount's Bay. Ibid., p. 166. BoASB, Dr. II. S.— Some Ohservations on the Alluvial Formations of the Western Part of Cornwall , Ibid., vol. iii., p. 17. Cabnb, J.— On the Granite of the Western Part of Cornwall. Ibid., p. 206. Hawkins, J. — On the Intercourse which subsisted between Cornwall and the Commercial States of Antiquity ; and, On the State of the Tin-trade during the Middle Ages. Ibid., vol. iii., p. 113. 1829. Oetnhausen, C. von, and H. von Dechbn. — On the Junction of the Granite and Killas Rooks of Cornwall. Phil. Mag., n.s., vol. v., p. 161. 1832. BoASB, Dr. H. S.— Contributions Towards a Knowledge of the Geology of Cornwall. Trans. Roy. Geol. Soc, Corn., vol. iv., pp.352— 359, Cabne, J.— a Description of the Stream Work at Drift Moor, near Penzance. Ibid., vol. iv., p. 47. 1834. BoASE, Dr. H. S. — Treatise on Primary Geology. 8vo. 1836. TdoKB, A. W.— The Mineral Topography of Great Britain, Mining Review, No. viii., p. 253. 1839. De la Beche, Sir H. T. — Report on the Geology of Cornwall, Devon, and West Somerset. Geol. Survey, 8vo, London. 1841. CoiTHTENAT, J. S.— Statistical Remarks on St. Just. 9th Eep. Com. Polytech. Soc, p. 91. 1843. Henwood, W. J.— On the Metalliferous Deposits of Cornwall- and Devon. Trans. Roy. Geol. Soc. Corn., vol. v; 1846. Carne, J. — Notice of the Remains of a Submarine Forest in the North Eastern Part of Mount's Bay, Ibid,, vol. vi., p. 230. 1850. AtJSTEN, R. A. C. [Godwin]— On the Valley of the English Channel, Quart. Journ. Geol, Soc., vol. vi., p. 69. 1851, On the Superficial Accumulations of the Coasts of the English Channel and the Changes they Indicate. Ibid., vol. vii., p. 118. Db la Beche, Sir H. T.— Geological Observer. 8vo. London, 1864, Caenb, Miss E. — On Transition and Metamorphosis of Rocks in the Land's End District. Trans. Roy. Geol. Soc., Corn., vol. ix., p. 1. 1871, Allpoet, S.— On the Microscopical Structure and Composition of a Phonolite from the Wolf Rock. With an Analysis by J. A. Phillips. Geol. Mag., vol. viii., pp. 247, 336. Collins, J. H. — A Handbook of the Mineralogy of Cornwall and Devon. 8vo. Truro. 1873. Baenett, a. K. — Observations on the Elvan Courses, Greenstones and Sandstones of Cornwall, with remarks on the associated Minerals, 4ist Ann. Rep. Roy. Corn. PoUjtech. Soc, p. 143. 1874. BoRLASE, W. C— Historical Sketch of the Tin Trade in Cornwall, from the Earliest Period to the Present Day. Plymouth. Whitaker, W. — List of Works on the Geology, Mineralogy, and Palaeontology of Cornwall. Jomn. Roy.Jnst. Corn., p. 61. 1875. Caene, Miss • E.— Enquiry into the nature" of the Forces that have acted on the formation and elevation of the ' Land's End Granite. Trans. Roy. Geol. Soc. Corn., vol. ix., p. 132. GiLBEET, Capt. J. — Notice of a Vngh in St. Ives Consols Mines. Ibid., p. 158. Phillips, J. A.— Rocks of the Mining Districts of Cornwall, and their relation to Metalliferous deposits. Quart. Journ. Geol. Soc, vol. xxxi., p. 319. 1876. Allpoet, S.— On the Metamorphic Rocks surrounding the Land's End Mass of Granite. Ibid., vol. xxxii., p. 411. PHiLLiPff, J, A.— On the so-called "Greenstones" of Western Cornwall. Ibid,, vol, xxxii., "p. 155. APPENDIX. • 145 1879. Foster, 0. Le Neve. — On a rook resembling LuxuUianite from St. Just ; and on some Globular Masses of Schorl-rock from Ding- Dong Mine. Trans. Boy. Geol. 8oc. Corn., vol. x., p. 8. UssHEE, W. A. B.— The Post Tertiary Geology of Cornwall. Svo. Privately printed, Hertford. ^Historical Geology of Cornwall. Geol. Mag., pp. 27, 74, 102, 166, 203, 251, 307. 1880. Phillips, J. A. — On Concretionary patches and fragments of other rocks contained in Granite. Quart. Journ. Geol. Soc, vol. xxxvi., pp. 1 — 22. 1881. Collins, J. H.— On the Geology of Central and West Cornwall. Journ. Roy. Inst. Corn., p. 18. 1882. On Some Cornish Tinstones and Capels. Journ. Min. Soc, vol. iv., pp. 1 and 108. 1882. Whitlbt, N. — The evidence of Glacial Action in Cornwall and Devon. Trans. Boy. Geol. Soc. Corn., vol. x., p. 132. 1884. Collins, J. H., and H. F. Collins. — On the Geological Age of Central and West Cornwall (2nd paper). Journ. Boy. Inst. Corn., p. 162. Collins, J. H. — On Some Cornish Tinstones and Capels. Journ. Min. Soc, vol. v., p. 121. Hunt, E. — British Mining. 4to. London. 1885. Millet, P. W. — Notes on the Fossil Poraminifera of the St. Erth Clay Pits. Trans. Boy. Geol. Soc. Corn., vol. x., p. 213. Wood, S. V. — On a New Deposit of Pliocene Age at St. Erth, 15 miles east of the Land's End, Cornwall. Quart. Journ. Geol. Soc., vol. xli., p. 85. 1886. Kendall, P. P., and R. G. Bell.— On the Pliocene Beds of St. Erth. Ibid., vol. xlii., p. 201. Millet, P. W. —Additional notes on the Poraminifera of the St. Erth Clay Pits. Trans. Boy. Geol. Soc. Corn., vol. x., p. 222. Eeid, C. — On the Pliocene Deposits of North-Western Europe. Nature, vol. xxxiv., p. 341. 1887. Bell, JR. G.— The Pliocene Beds of St. Erth. Trans. Boy. Geol. Soc. Com., vol. xi., p. 45 ; {Brit. Assoc.) Geol. Mag., p. 468. Collins, J. H. — Sketch of the Geology of Central and West Corn- wall. Proc. Geol. Assoc, vol. x. 1888. Harris, G. F. — Granites and our Granite Industries. Svo. London. [Chapter iv., Cornwall.] Teall, J. J. H. — British Petrography. Svo. London. 1890. Reid, C— Pliocene Deposits of Britain. Memoirs Geol. Survey. Teall, J. J. H. — Metamorphism in the Hartz and west of England. Trans. Boy. Geol. Soc Corn., vol. xi., p. 221. 1892. Collins, J. H. — On the Pinite of Breage in Cornwall. Journ. Min. Soc, X., p. S. Peestwich, Sir J.— The Raised Beaches and "Head" or Rubble- drift of the South of England; their Relation to the Valley Drifts and to the Glacial Period ; and on a late post-glacial Submergence. Quart. Journ. Geol. Soc, vol. xlviii., p. 263. 1895. Millet, F. W.— Tlie Poraminifera of the Pliocene Beds at St. Erth. Trans. Boy. Geol. Soc Corn., vol. xi., p. 655. 1896. Phillips, J. A., and H. Louis. A Treatise on Ore Deposits. 2nd Edition. Svo. London. 1897. Millet, F. W. — The Poraminifera of the Pliocene Beds of St. Erth in relation to those of other deposits. Trans. Boy. Geol. Soc. Corn., vol. xii., p. 43. 1898 Bell, A.— On the Pliocene Shell-Beds at St. Erth. Ibid., vol. xii., p. lil. Millet, P. W. — Additions to tiie List of Poraminifera from St. Erth. Ibid., vol. xii., p, 174. 1899. Hill, J. B.— In "Summary of Progress for 189S." Mem. Geol. Survey, p. 97. 1900. Hutchinson, A. — On Stokesite, a new mineral containing tin, from Cornwall. Journ. Min. Soc, vol. xii., p. 274, 9564 ^ 146 ' GEOLOGY OP land's END. 1904. J'lbtt, Dr. J. S.— First Notes on the Petrography of Western Cornwall. " Summary of Progress for 1903," p. 150. Mem. Geol. Survey. Low, Dr. J. Spencer. — Report to the Local Grovernment Board upon the Sanitary Circumstances and Administration of the Eight Sanitary Districts comprised within the Penzance Kegistration District (No. 200). Pol. Byre and Spottiswoode, Is. Reid, C— On the probable Occurrence of an Bocene Outlier ofi the Cornish Coast. Quart. Journ. Geol. Soc, vol. Ix., p. 113. Reid, O. and B. M. — A probable Palseolithic Floor at Prah Sands. Ibid., vol. Ix., p. 106. 1905. Andrews, A. W. — Climbing on the Cornish ClifEs. Climbers' Gliib Journ., vol. vii., pp. 55 — 67. [Illustrations of ClifEs around Zennor.] 1906. Stkutt, Hon. R. J. — On the Distribution of Radium in the Earth's Crust, and on the Earth's Internal Heat. Proc. Royal Soc. Ser. A., vol. Ixxvii., p. 472, and vol. Ixxviii., p. 150. Hill, J. B. — On the Relation between the Older and Newer Palaeozoics of West Cornwall. Gfeol. Mag., p. 205, INDEX. Abraham, Wheal, 102. Actinolite, 33, 34. Adinoles, 26, 27, 29. Agriculture, 1. Alfred Consols, 99, 100, 123, 134. , Wheal, 64, 96, 98, 100, 123, 134. Alice, Wheal, 123. AUport, S., on greenatones, 31, 36, 87 ; metamorphic rocks, 20, 21, 23, 25, 27, 28 ; the Wolf Rock, 70, 71, 144. Alluvium, 77, 78, 81, 82. Alteration caused by elvans, 20, 61 ; by granite, 7, 8, 10—26, 31, 34— 39, 42, 43, 45, 53 ; by greenstone, 11, 12, 15, 16, 20, 26—30 ; pneuma- tolytic, 53—60. Amalebrea, granite of,. 46; lodes near, 98. Amphlbole, 27, 28, 36, plate 5. Analyses of altered slates, 29, 30, 60; of granite, 59, 60 ; of greenstone, 35, 60. Andalusite, 17, 23—25, 30, 52, 53 ; alteration products after, 22. hornfels, plates, 5, 6. Andrews, A. W., on Cornish cliffs, 146. Ann, Wheal, 100. Anne, Wheal, 123. Anticlines, 7, 10, 14, 62. Antimony, 103. Apatite, 24, 33—35, 37, 48, 50, 52, 53, 56, 57, 59, 66. Aplite, 52—54. Arctic conditions, 78, 81. Area described, 1. Argus, Wheal, 123. Arsenic, 97, 100, 103, 104, 106, 107, 109, 116, 134 ; yield of, 122. Arthur, Wheal, 123, 134. Asbolane, 118. Atlantic swell, effects of the, 74, 77, 83, 84. Augite, 32-34, 37, 38,39. Augite-andesites, 35. Augusta, Wheal, 123. Aureole of metamorphism, 7 — 9, 12—26; outer limit of the, 7, 10, 11, 17 — 19 ; relation of the lodes to the, 85, 86, 93, 94 ; thickness of the, 8, 40, 46, 49. Austin, B. A. C. [Godwin-], on the English Channel, 144. Axinite, 27, 32, 34, 38, 39. Bal, Wheal, 123. Balleswidden Mine, 95, 97, 98, 100, 101, 123. Ballowall Cliff, mine at, 116. 9564 Balnoon Mine, 97, 101, 123. Banded slates, 7, 9, 19. structure in elvans, 61 — 62, 65. Banffshire, phyllites compared, 27. Barham, T. F., on Iktis, 144. Barnett, A. K., on elvans, etc., 144. Barrow, G., on erratics in Soilly, 78 ; on folded rocks, 6. Battery Rocks, 16. Wharf, 87. Beaches, modern, 68, 69, 75 ; raised, 75-79. Beagleton Downs, granite of, 46. Bearing of the lodes, 98, 99. Bedding in granite, 41 — 43; in slate, 6,20. Bell, A., on Pliocene of St. Erth, 71, 145. , R. G., on Pliocene of St. Erth 72, 145. Bell Mine, 101. Bellan, Wheal, 97, 101, 102, 123. Bessack Rocks, 19. Bezurrel, elvan of, plate 6. Billia Consols, 123. Binner Downs, anticline of, 10. Mine, 96—99, 102, 104, 123, 134. Wood Mine, 123. Biotite, 7 - 9, 11, 21-24, 28, 30, 32, 35-38, 47, ,50-53, 65, 67, plates, 5,6. trachyte in raised beach, 76. Bismuth, 100, 103, 106—109, 117. Black Cliff, 19, 20. tin. See Tin. Blende, 96, 100, 103, 104, 106, 107, 117, 118, 134. Boase, Dr. H. S., on alluvial de- posits, 81 ; the geology of West Cornwall, 143, 144, on jointing, 63. Bohemia, china-clay of, 47. Boiling Well Mine, 98, 123, 134. Bolton, Wheal, 102, 123. Bonney, Prof. T. G., on luxuUianito, 56. Boric vapours, 20, 37—39, 54. Borlaae, Rev. W., on Cornish geology, 143 ; flint-gravels, 68 ; St. Just Mines, 96, 97, 103; Wherry Mine, 118, 133. ; W. C, on the tin-trade, 144. Boscaswell Mine, 98, 102, 115, 123. Boscawen Point, greenstone of, 77, Boscean Mine, 104, 114, 123. Boscregan lodes. 111. Bosom and Ballowall Mine, 123. Bosparva, lodes near, 99. Bossiliack lode, 104. L 2 148 INDEX. Boswedden Mine, 102, 115. and Castle Mine, 123-125. Place, lode at, 104. Bosworgy Mine, 124. Botallack, cordierite at, 24 ; garnet at, 38, 39; granite of, 59 ; bornfels of, plate 5 ; liornstone of, 26, 27. Head, altered rocks of, 13. Mine, 93, 95—98, 102-104. 124, 134, plate, 2. Boys, Wheal, 98. Brandys, mines near the, 98. Brea Consols, 103, 124. Breage, cross course near, 88. mines, 100, 107, 127, 138. Breccias in greenstone, 34, 36 ; in lodes, 95-97 ; in slate, 19, 27. Bronze Age, 85. Building stone, 1, 46, 47, 89, 90. Bunches of ore, 97. Burnt Downs, lodes near, 98. Bussa lode, 105. Busz, Prof., on cassiterite in granite, 52 ; cordierite at Luxullian, 52. Calamine, 100. Calcareous bands in slates, 7, 45. Call, Wheal, 102. Camborne, mines of, 3, 85, 138. Cambrian rocks, 6. Canon's Town, elvan at, 63 ; mines at, 93, 122; Pliocene deposits near, 73 ; slate of, 17. Cape Cornwall, drift of, 76 ; granite of, 44 ; granite veins of. 44, 57 ; lodes near, 93 ; metamorphic rocks of, 12-14, 23, 24, 26, 27, plate 6 ; tourmaline st, 25. and St. Just Consolidated Mine, 117, 124. Carbis Bay, granite near, 11, 47, 55, 56, 60, 91, plate 6 ; greenstone of, 11 ; lodes at, 11, 86, 87,98 ; mines near, 93, 95, 98 ; raised beach of, 76 ; slate of, 10, 11, 13 ; topaz near, 53. Oarbonas, 86, 87, 96, 115, 116, Carbona Mine, 124. Carboniferous Period, 4. Carew, JR., Survey of Cornwall, 118, 143. Carfury, granite of, 89. Carlsbad twins, 32, 50, 65, Carnabargas, greenstone of, 33, Carnaquidden, granite of, 46. Carn-du, granite of, 43. Carne, Miss E., on the Land's End, 144. J., on alluvial deposits, 81, 82 ; Cornish geology, 143, 144 ; mines, 100, 102, 103, 107, 108, 111, 115; pebbles in Ding Dong Mine, 106 ; St. Michael's Mount, 83, 84 ; tin- floors, 97. Carne, Wheal, 124. Carnelian, 68. Carnelloe Mine, 103, 124. Carn Galver Mine, 94, 124. Carnleskis Mine, 127. Carnmeal Mine, 99. Carnmenellis, mines near, 93. Cams, 46. Carnyorth Mine, 93, 103, 104, 124. Moor, guide on. 111. Caroline, Wheal, 99, 124, Carpenter, Wheal, 99. 124, 134. Carrack Dhu Quarry, 90. Gladden, slate of, 11. Carrick Du, greenstone of, 33, 34, 39, 60. Mine, 104, 124. Symons's, 15. Carzise Mine, 104, 124. Cassiterite, 48, 52, 55—58, 66, 67, 87. See also Tin. Castle-an-Dinas, granite of, 46, 47, 49, 89, 90. — — Giver Cove, 19. , Wheal, 102, 124. 134. Gaunter lodes, 88, 99, 102. Celestine, 102, Ceres Bocks, 19. Chalk-flints, 68, 69, 75-77. Chalybite, 100. Charcoal in the Head at Prah Sands, 80, 81. Charlotte Mine, 99. Ohenhalls, greenstone of, 33, 37, 38, 39. Chiastolite, 23. Chilled margin of elvans, 61—63, 65. Chimney Rock, elvan of, 63. China-olay, 5, 47, 89. stone, 58. Christopher, Wheal, 124. Chyandour, altered slate of, 16; greenstone of, 33, 36— 39, 91, plate 5 ; hornblende slate of, 29 ; sub- merged forest of, 82. Chymorvah, greenstone of, plate 5. Chypraze Consols, 124. Cleavage, 7-9, 13, 16, 20, 61, 62; relation of lodes to, 97. Cliffs, height of, 2, Oligga Head, topaz at, 48. Climate, 1 ; former, 78, 81, 83. Clowance Gaunter, 99. , Wheal, 124. Cobalt, 103, 107, 118. Cook, Wheal, 93, 98, 102, 103, 123. Cockle, 103. Collins, J. H., on the mineralogy and geology of West Cornwall, 5, 144,145. Concretionary, action in metamor- pbism, 23, 24. INDEX. 149 Conglomerate, Tertiary, 73, Contact alteration caused by elvans, 20, 61 ; by granite, 7—26, 31, 34—39, 43, 45; by greenstone, 11, 12, 15, 20, 26—30. Contemporaneous igneous rocks, 33. Contortion, 6, 7, 9, 10, 16, 20. Contours, 1—4. Coombe Cottage, greenstone at, 16. , The, 15, 16. Copper lodes, 11. 85—87, 93, 96, 100—104, 106-118. , native, 117, 118. statistics, 112, 122—132. Copper Bottom lode, 98. Copperhouse, slate of, 20. Coralline Crag, 73. Cordierite, 9, 13, 23—25, 28, 30, 49, 50, 52, plates 5, 6 ; alteration pro- ' ducts after, 22, 24 ; in elvans, 65. Cornubianite, 25. Corrosion of quartz - crystals in elvan, 65. Corundum, 24, 25, 30. Country rock, 13, 95. Oourtenay, J. S., on St. Just, 144. Courtis, Wheal, 99. Cowloe, 14. Crebor, Wheal, 125. Crenver, Wheal, 102. Cressars, The, 17, 63. Cretaceous material in drift, 68, 69, 75-77. Cross- courses, 88, 96, 99, 100. Cross-shaped felspar twins, 41, 50. Crowan, mines in, 117, 125, 138 ; iron-ore at, 122. Crowlas, elvan at, 64; granite of, 46; spotted slate of, 17. Crowns Mine, 93, 102, 103, plate 2. Crush-breccias, 27, 34, 95. Cudden Point, greenstone at, 10. Cunning, Wheal, 104, 125. Darlington, Wheal, 64, 82, 99, 104, 125. Dartmoor, Eocene rivers of, 70, granite of, 52. Davy, Sir H., on Cornish geology, J., on granite veins, 143. Deadman's Cove, 19. Decalcification of shell sand, 75, 76. De la Beche, Sir H. T., on correla- tion of rocks, 4 ; granite viens, 45 ; lodes, 97 ; Report on the Geology of Cornwall, etc., 4, 5, 144. Denudation, 69, 70, 78, 81, 83, 84. Devon, Eocene of, 68, 69 ; Permian volcanic rocks of, 76. Devonian rocks, 4, 6. Diabase, 32, 35, 36. hornfels, 32, 35, 37. porDhyrites, 32. Diabase schists, 32, 34. Diluvial theory, 5. Ding Dong Mine, 85, 94, 98, 104, 105, 122, 125. Diodorus Sioulus on lotis, 83. Dips. 6, 7, 9 ; of elvans, 63, 65, 88 ; of greenstone sills, 9, 10. Dixon. B. B. L., on elvans, 64 ; the Falmouth Series, 18 ; greenstones, 10 ; isolated metamorphic areas, 8, 17- 19, 22 ; Portsoatho sand- stone, 18, 19 ; raised beach, 75, 76. Dorset, Eocene of, 69. Drannock, Wheal, 107. Drea, Wheal, 106. Drewlas, Wheal, 125. Drift, 5, 75—83. Duffleld Mines, 95, 96. Dumpling, Wheal, 82, 83, 99, 125. Dunes, 82, 83. Durlo, Wheal, 125. Dykes, elvan, 61—67. Bast Alfred Consols, 125, 134. Balleswidden Mine, 125. Boscaswell Mine, 125. Bosom Mine, 125. Botallock Mine, 125. ■ Godolphin Mine, 125. Hallamanning Mine, 125. Levant Mine, 96, 125. New Rosewarne Mine, 125. Providence Mine, 125. Relistian Mine, 106, 125. Eosewarne Mine, 126, 134. St. Just United Mine, 126. Strawberry Mine, 126. Tregembo Mine, 119. Trenoweth Mine, 126. Wheal Cock, 106, 125, 126. Fortune, 99. Grylls, 125. Kidney, 125. Margaret, 106, 125. Eastern Green, 83. Economic geology, 85 — 142. Edward, Wheal, 98, 106, 126. Elizabeth, Wheal, 106. Elvans, 4, 9, 16, 61—67; use of term, 61 ; used for building, 90 ; con- vergence of, 86 ; decomposition of, 66 ; distribution of, 62 ; masses in lodes, 95 ; metamorphism pro- duced by, 20, 61 ; as ornamental stone, 91 ; photomicrograph of, plate 6 ; relation to lodes, 98 ; as road metal, 90 ; tin-ore in, 86—88 ; 107, 118 ; water-supply from, 91 ; width of, 62-65. Emily, Wheal, 134. Ennys Wheal Virgin, 99. Eocene, 5, 68—71. Epidote, 27, 32—34, 38, 39. Escall's Green, elvan at, 6? 150 INDEX. Falmouth, Geology of, 5. Slates, 5-7, 18, 19. Faults, 88, 99, 102, 104 ; coinciding with lodes, 88. Felsite, 61-67. Felspar, cross-shaped twins of, 41, 50 ; phenocrysts, 50, 65 ; rock, 43. Felspathic grit, 19, 20. Fire, traces of, in Palseolithic de- posit, 81. Fishing Cove, 19. Flints in Cornwall, 68, 69, 75—77. Floods, 78. Floors of tin-ore, 97, 103, 118. Florence Consols, 106, 126. , Wheal, 99, 126, 134. Flower culture, 1 . Pluccans, 101. Fluoric vapours, 20, 37, 38, 54. Fluorspar, 38, 39, 49, 53, 54, 104, 107. Fluxion structure in el vans, 61 — 63, 65 ; in granite, 41, 42, 44, 49 ; in greenstone, 33. Folding, 6, 7, 9, 10, 16, 19, 20, 61, 62. Foliation in greenstone, 34 ; in phyllite, 21. Forbes, Dr. J., on Land's Knd and St. Michael's Mount, 48, 143; Wherry Mine, 118; Whitesand Bay, 43. Formations, table of, 3. Fortune, Wheal, 96. 100, 126. Foster, Sir C. Le N.j on Balleswid- den Mine, 100, 123; boulders in lodes, 96, 97, 145; Ding Dong Mine, 104, 106, 145 ; luxuUianite, 145 ; New Kosewarne Mine, 96, 97. Fossils, absence in slates, 4 — 7, 9. in the raised beach, 75, 76. , Pliocene, 72—74. Fox, Howard, on the Runnel Stone, 14. Fraddam, Mines near, 98. Friendship, Wheal, 99, 119, 126, 127. and Prosper Mine, 126. Frost, effect of, 78, 81. Fnichtschiefer, 21. Gala Rocks, drift near, 76. Galena. See Lead. Garbenschiefer, 21. Garnet, 9, 12, 25, 27, 32, 34, 39, 45, 109, 111, plate 3, Garth Mine, 106, 125, 126. Gateposts, 41, 46, 89. Geological Photographs Committee, 45. Society, illustrations lent bv the, 2, 69, 72, 80. Structure of the area, 3. Georgia Mine, 98, 99, 106, 126, 138. Germoe, mines in, 138. Giant granite, 47, 49, 53, 66. Gilbert, J., on St. Ives' Consols, 117, 144. Gilbertite in granite, 53. Gilbert, Wheal, 126. Gill, Wheal, 134. Gilmar, Wheal, 126. Glacial epoch, 4, 78 81. Goath vein, 101. Godolphin, granite of, 17, 48, 49, 93, 94, 98, 99. Cross, cross-course near, 99, 100. Hill, 2. ■ Mines, 93, 97, 106, 126. Godrevv, raised beach .of, 75, 76 ; slate of, 8, 18, 19. Goldsithney, elvan at, 65. Gook, 100. Goole Pellas Mine, 126. Gorran, fossiliferous rooks of, 6. Gossans, 88. Granite, alteration of greenstone by, 31, 32, 36-39; alteration of slate by, 7, 8, 9, 12-15, 18, 20— 26; cooling of the, 61, 62, 86; fine-grained, 43, 46, 47 ; intrusion of the, 4, 5, 7, 9, 10, 13, 14 ; joint- ing of the, 14, 41-43,89; killas inclusions in, 24, 25, 29, 30, plate 5 ; limits of the, 40, 43 — 46 ; masses in lodes, 95, 96 ; photomicrographs of, plate 6 ; radium in, 60 ; rela- tion of the lodes to the, 93, 94, 97 ; underground surface of the, 3, 7— li; 14, 17, 44, 49, 61, 85, 103; veins, 12—14, 42—45, 48, 49, 61, 62, 86, plates 1, 3; used for beams, 89 ; used for building, 89, 90 ; as an ornamental stone, ' 91 ; as road metal, 90. Granophyres, 66. Graphic structure in elvans, 66. Graphite, 22. Grauwacke, 4. Gready, granite of, 59. Great Godolphin Bridge Mine, 127. Trevegean Mine, 127. Western Mine, 99, 120, 127, 134. Wheal Alfred, 126, 134. Fortune. 102, 119, 126, 134. Grylls, 127, 130. Work Mine, 94, 99, 106, 107, 127, 134. Greenpease lode, 105. Greensand-chert in drift, 68, 69, 75-77. Greenstone, 5, 6, 9- 12, 15, 16, 31—39. 43, 44, 46 ; altering slates, 11, 12, 15, 16, 20, 26—30; chilled margins of, 33, 34, 36 ; date of in- trusion, 10 ; dip of the sills, 15, INDEX. 151 16 ; mefcamorphism of the, 31, 32, 36-39; microscopic structure of, 31- 39, plate 2, 5 ; strike of, 10 ; as ornamental stone, 91 ; as road metal, 90 ; use of the term, 31. Greisen, 26, 44, 45, 48, 54, 55, 57—59, 66, plate 6. Grey, Wheal, 127. Gribba Point, lodes near, 93. Gries, 100. Grylls, Wheal, 127. Florence, 127. Grylls' Bunny, 97, 103. Guides, 99, 100, 111. Gulval, altered slate of, 17 ; mines of, 138 ; old cliff of, 77. Downs, granite of, 41, 43, 46, 47, 89, 90. Gunwyn Quarry, 11,36. Gurlyn, Wheal, 99, 127. Gurnard's Head, greenstone and slate of, 12. Mine, 103, 117, 127. Guskus Mine, 99, 127. Gwallon Mine, 64, 99, 107, 127. Gwavas Quarry, 35, 36, 37, 90. Gwin and Singer Mine, 120, 127. Gwinear, cross-course near, 88 ; elvan at, plate 6 ; greenstone at, 10, 34 ; mines of, 93, 95, 98, 116, 139 ; spotted slate of, 22. Consols, 95, )27. District, mineral statistics of, 122. Downs, mines of, 93, 99. Gwithian, slate of, 21, 49 ; anticline at, 10 ; Red Eiver at, 3 ; mines in, 139. Halamanning Mine, 99. and Croft Gothal Mine, 127. Betallack Mine, 127. Haldon, cretaceous rocks of, 68, 69. Hall, T. C. photographs by, 45, plates 1 — 6. Halse Town, altered granite of, 45. Hampshire Basin, Eocene of the, 70. Hampton, Wheal, 99, 117, 127, 132. Harris, G. P., on granite, 145. Hartley, Wheal, 127. Harvey's Pit, 72, 89. Hawkes Point Mine, 11, 127, 134. Hawkins, J., on mines, 87, 97 101, 103, 118, 143, 144. Hawk's Point, spotted slate of, 11. Hayle, anticline at, 10 ; greenstone near, 33; sand-dunes near, 83; slate at, 7, 10, 20, 21 ; stone quar- ried at, 90. River, 3, 69, 76. Valley Mine, 127. Hazel-nuts in submerged forest, 82. Head, 71, 73, 76 -81, plate 4. Hea Moor, elvan at, 63. Hearle, Wheal, 120, 127. Heights, 1—3. Helena Mine, 132. Hell's Mouth, 19. Hendra, granite vein at, 46. Henwood, W. J., on elvans, 64, 65 ; guides, 100 ; mines, 87, 100—104, 106—108, 111, 113, 118, 144; on stockworks, 97. Herlaud Mine, 95— 98, 100, 107,127, 134 ; elvan in, 67. Hermon Hill Mine, 116, 127. Highland rocks, 6, 34. Hill, J. B., on the geology of West Cornwall, 5, 6, 145, 146. Hitchins, Rev. M., on Herland Mine, 143. Hoe Point, slate of, 17. Hone-stone of Gwithian, 21. Hopes, Wheal, 127. Hornblende, 28, 32, .33, 36, 37. schist, 15, 16, 34. slates, 29. veins, 27, 33. Hornfels, 5, 7, 8, 11—14, 17, 20-26, 36, 43, 45, 53, plates 3, 5, 6. Hornstone, 26. Howe Downs, lodes at, 98. Hudder Down, slate of, 18. Huel. See name of mine. Hunt, R.. on carbonas, 87 ; on min- ing, 145. Hutchinson, A., on stokesite, 145. Ice, action of, 4, 78, 81. Ictis, 83, 84. Ilmenite, 33, 34. Implements, Palseolithic, 81. Inch's Castle, quarry at, 47. Inclusions in granite, 24, 41,43, 45, 53. Index of mines, 135—142. Iron ores, 96, 122, 134. Iron pyrites, 122, 134. Island, drift of the, 76. Jars, M. G., Voyages Metallurgiques, 143. Jasper, 102. Jennings, Wheal, 97, 107, 116, 128, 129 Jointing, 41—43, 57, 61—63, 99. Julia, Wheal, 97, 117. Kaolin, 40, 48,50, 51, 89, 100, 106, 114. Eaolinisation, 58, 60—67. Kayle, Wheal, 108, 128. Keethan, 102. Kelynack, Wheal, 128. KenddU, P. F., on Pliocene of Brth, 72, 145. Keuidjack, cordierite hornfels at, 13, 24, 28 ; lode at, 115. Kenneggy, mines near, 94, 128. Kerbs of granite, 41. 152 INDEX. Kestal, lodes at, 99. Kettle's Bottom, 14. Killas, age of the, 4, 5 ; description of the, 6—30; divisions of the, 5—7 ■ thicliness of the, 6—9 ; altered by granite, 5, 7, 8, 11—14, 17, 20—26. 36, 43, 45, 53, plates 3, 5, 6; altered by greenstone, 11, 12, 15, 16, 20, 26—30 ; inclusions in granite,24,41, 43, 45, 53 ; radium in, 60. Kine, Wheal, 107. Kitty, Wheal, 128. Knill's Monument, granite at, 47, 60, 91, plate 6 ; mines near, 93, 95, 98 ; topaz at, 53. Knotted slates, 9, 11 — 13. Laccolites of granite, 3. Lambo Mine, 99, 128. Lamin Mine, 128. Lamorna, drift of, 77 ; granite of, 24, 40—42, 49, 53, 59, 60, 89 ; in- clusions of slate in granite of, 29, 30, 41, 53. Land's End, 14; cliffs of, 40, 43, plate 1 ; elvan of, 62, 91 ; granite of, 49, 89, 93 ; raised beaches of, 75, 77 ; schorl veins of, 48. Lanyon Moor, water from, 91. Latham, Mr., on elvan near Pen- zance, 63. Lead-ore,- 122, 134. Lean, Capt. J., on unwatering mines, 101, 102, 104, 108, 113,116, 117. Leeds and St. Aubyn Mine, 17, 99, 128. , Wheal, 128. Leedstown Consolidated Mines, 128, 134. , metamorphio spotting near, 8. Lelant Cliffs, 20. Consols, 113,128. Towans, 10, 83. Lemon, Wheal, 128. Lenham Beds, 73. Lesceave, altered rooks of, 23. ■ — • — Por, topaz at, 53. Lescudjack, greenstone of, 33. Lencoxene, 32, 33, plate 5. Levant, breeciation near, 34. , garnet at, 38, 39. — — , junction of granite and slate at, 44. Mine. 56, 86, 93, 95, 96, 98, 108, 112, 117, 128, 134. Zawn, 111. Lewis Mines, 99, 128. Lintels, granite used for, 41, 46. Literature, 4, 5. Lithia-miea, 49, 51, 54. Little Bounds Tin Mine, 113 Llandeilo fossils, 6. Locke, Wheal, 128. Lodes, connection with the granite 42, 85, 86, 93, 94 ; distribution of, 85, 93, 94 ; formation of, 86 ; influ- ence of, on granite, 42 ; origin of, 95—98 ; seen in the cliffs, 11—13. Logan Rock, 43. Long Kock, 17, 63, 64. Longships, 14, 43. Lonsdale, W., on the Devonian system, 4. Loss of land, 83, 84. Louis, H., on ore-deposits, 145. Low, Dr. J. S., oa water supply, 91, 92j 146. Lower Pentreath, altered rooks of, 23. Lucy, Wheal, 98, 128. Ludgvan, chalk-flints at, 68, 69 ; elvan at, 63 ; greenstone of, 14 ; metamorphism at, 17 ; mines in, 139; old cliff of, 77; slates and greenstone of, 10. Lease, elvan at, 64. Parish Quarry, 47. Luxullianite, 56, 66, 91, 104. MacAlister, D. A., on mining and statistics, 86, 93-142. McGrigor, G. D., on the Perran silver mine, 88. Madron, elvans of, 62 ; granite of, 46 ; lodes near, 98 ; mines in, 94, 139. Magow Rocks, raised beach of, 76. Majendie, A., on the coast west of Penzance, 143. Malkins lode, 104, 105. Man-engines, 112. Manganese, i03. Marazion, building stone of, 47 ; flint-gravel near, 68, 69 ; fore- shore near, 16, 17 ; greenstone at, 10, 33, plate 5 ; head at, 78 ; mines in, 94, 96, 99, 113, 122, 128, 139 ; raised beach of, 75, 77 ; recent changes near, 83, 84; submerged forest of, 82. Marsh, 83, 84; elvans under, 64 ; lodes under, 99. Margaret, Wheal, 128. Margery, Wheal, 113, 128, 134. Marine erosion, 83, 84. Market gardening, 1 . Mary, Whtal, 92, 128. . — — and Kitty United Mine, 128. Matthews, T., on the Longships, 14. Mediterranean affinities of the St. Erth fauna, 73. Mellanear Mine, 98, 113, 128, 134. Mellanoweth Mine, 113. Menedarva, sandstone near, 19. Merth, Wheal, 98, 106. Messinian, 73. Metal, Wheal, 93, 99. INDEX. 153 Metamorphio rocks, 3, 5, 7, 8, 11 — 14, 17, 20—26, 36, 43, 45, 53, plates 3, 5, 6 ; hardness of the, 43,44. aureole, 20 — 26 ; relation to lodes, 85, 86, 93, 94 ; width of, 40. Metamorphism caused by el vans, 61. of greenstone by granite, 31, 32, 36, 37. Metasomatic action, 26, 54. Mica veins, 49. Microcline, 51. Micrographio fringes, 66. Mill Bay, granite of, 56. MiUett, Wheal, 99, 113, 134. Millett, P. W., on Pliocene of St. Erth, 145. Millpool Mine, 99, 128. Minerals, 93, 142. Mineral statistics, 87—89, 100, 103, 111,112,118,122-132. veins. See lodes. Miner's paths, 13. Mines, distribution of, 93, 94 ; elvans proved in, 61, 64, 65; index of, 135 — 142 ; water-supply from, 91, 92. Mining, 1, 85—88, 93—121. and Smelting Magazine, 130. Miocene earth - movements, 70 ; strata, 73. Mispiokel, 100. Mollusoa, Pliocene, 72—74. Molybdenite, 118. Morvah and Zeunor United Mines, 94, 113, 129. Consols, 129. , Mines near, 98, 122, 139. Moulding sand, 72, 89. Mount's Bay, 1, 2, 69, 70 ; drift of, 77, 78 ; foreshore of, 16, 17 ; recent changes in, 83, 84 ; sand dunes of, 82, 83 ; submerged forest of, 82. Consols, 129. Mousehole, granite of, 42 ; green- stone of, 38 ; greisea of, 57 ; killas of, 14, 15 ; mines near, 118 ; raised beach near, 77, plate 4 ; schorl- rook of, 25, plate 6. Moyle, M. P., on granite veins, 144. Mullion, flints at, 69. Murohison, Sir E. I., on the Devonian system, 4. Muscovite-tourmaline schist, 26. Museum of Practical Geology, 13, 90, 91. Mylor slates, 5, 6-18, 62, 90. Nancecothan and Avrack Consols, 113. Nanceddan, granite of, 46. Nancemellin, sandstone near, 19. Nanoothan, disturbance near, 15. Nanturras Mine, 129. Narrow lode, 103. Navax Point, slate of, 18, 19. Negative crystals of quastz, 51. Neptune, Wheal, 88, 99, 114,129. Newlyn, absence of elvans near, 63 ; greenstone of, 33 — 36; hornfels of, 15, 28, 42, 90 ; hornstone of, 26, 27 ; mines near, 118 ; raised beach of, 76, 77 ; road-metal of, 90 ; strike at, 62. Newmill Quarry, 41, 53, 89, plate 6. Newquay, fossiliferous rocks of, 4, 5 ; greenstones of, 39. Newtown Brick Works, 64. , lode at, 104. New Balleswidden Mine, 101, 129. Great Work Mine, 129. Rosewarne Mine, 96—98, 114, 129. Trumpet Consols, 129. West Eosewarne Mine, 129, 134. Wheal Vaddon, 129, North Battery Tin Mine, 114. Godolphin Mine, 129. Great Work Mine, 129. Levant Mine, 129, 134. Eosewarne Mine, 98, 129, 134. Wheal Unity, 129. Occupations, 1. Ochre, 122, 134. Oeynhausen, C. von and H. von Deohen, on the junction of the granite and killas, 144. Old Bal lode, 98. Great Work Mine, 129. ■ men, mining by the, 86, 102. Wheal Neptune, 129. Opal, 102. Ophitio structure in greenstone, 33. Ordovician system, 6. Ore-deposits, 4, 5, 85—88, 93—121 ; relation to the granite, 7, 8, 85 ; successive deposition of, 95 —97. statistics, 100, 103,111, 112, 122 —132. Orientation of the felspars ingraijite, 41, 42, 49. Ornamental stones, 91. Orography, 1—4. Orthoclase phenocrysts in granite, 41, 42, 48—50, 65. Osborne, Wheal, 93, 99, 129. Overthrusting, 6, 11. Owen Vean Mine, 99, 129. Owles, Wheal, 98, 114, 115, 129, 134. Pack ice, effects of, 78. Palseolithic remains, 78 — 81. Parbola Mine, 107, 129. Paris, J, A., on consolidated sand, 143. Parknoweth Mine. 114, 129. 154 INDEX. Paul, granite of, 41, 42 ; greenstone near, 90 ; mines in, 129, 139. Hill, green bands of, 15, 29. Peach, 102. Pedn-men-du Point, 43. Pegmatite, 47, 49, 53, 66. Penberthy, Consols Mine^ 115. Crofts Mine, 99, 129, 134. Penbertliy, Capt., on Wheal Provi- dence, 11 116. Pendeen, cliffs of, 12, 13 ; granite near, 44 ; lodes at, 93, 98. Consols, 115, 129. Pendour Cove, Drift of, 76. Penlee, greenstone of, 14 — 16, 34 — 36, 39, 90, plate 4 ; raised beach of, 77, plate 4 ; slate of, 14—16, 26, 27. Penolver Quarry, 15, 90. Penzance, blown sand at, 83 ; build- ing stone used in, 46, 90; china-clay shipped at, 89 ; clay used at, 71 ; cross course near, 88 ; elvans of, 62, 63 ; flint-gravels near, 68, 69 ; granitenear, 40, 41,89, 90; green- stone near, 9, 31, 34 — 36, 91, plate 5 ; mines near, 85, 87. 94, 106, 118, 139 ; raised beach of, 75, 77 ; re- cent changes near, 83, 84 ; shearing near, 15, 16 ; submerged forest of, 82 ; water supply of, 63, 91. Consols, 129. District, mineral statistics of the, 122. Permian volcanic rocks, 76. Perran Downs, elvan at, 64. Silver Mine, 86, 88, 134. Perranporth, topaz near, 48. Perranuthnoe, elvan at, 64 ; green- stone at, 10 ; mines near, 88, 93, 96, 99, 122, 139. Downs Mine, 96. Petrology of elvans, 65—67 ; of granite, 49—60 ; of greenstones, 31 —39; of Mylor slates, 7, 20—30. Phenocrysts in elvans, 65 ; in granite, 41, 42, 48—50. Phillack, mines in, 100, 108, 140; slate of, 20. Towans, 76, 83. Phillips, J. A,, analyses of granite by, 59 ; on greenstones, 5, 15, 31, 34, 35, 144 ; on hornblendic slates, 29; on inclusions in granite, 24, 25 ; on ore-deposits, 144, 145 ; on the Wolf Rock, 71, 144. W., on Herland Mine and Wheal Alfred, 100, 143, and Darlington, Messrs., min- eral statistics, 123, 124, 126, 128. Phonolite, 70, 71. Phyllites, 7, 21—23. Physioial features of the area, 1-4. Pie lodes, 101. Pinite, 24, 40, 44, 46, 47, 49, 50, 52, 64—67, 90, plate 6. Pitch of folds, 19, 20. Pitchblende, 86, 87, 106, 114, 117. Playfair, Prof. J., on granite veins, 143. Pleistocene, 5, 75—83. Pliocene, 1—5, 69-75, 78. Plymouth, fossiliferous rocks of, 4, 5. Pneumatolysis, 30, 37—39, 53—60, 66, 67, 86. Poljigga, elvan at, 63. PoUadras Downs Mine, 98, 115. Pollard, Dr. W., analyses by, 30, 35, 59, 60. Polrose Mine, 129. Population, 1. Porphyritic crystals, removal by straining, 42, 61 , orientation of , 41 , 49 ; in elvans, 61, 62 ; in green- stone, 34. Portheras Cove, granite of, 12, 44 '; drift of, 76. Porthleven, china-clay shipped at, 89 ; granite under, 49. Porthmeor, drift of, 76 ; granite of, 12, 44, 45, plate 3 ; greenstone of, 37 ; killas of, 23, 24, 44, 45. Porthminster Point, 11. Porthzennor, granite of, 45. Perth Curnow, elvan at, 62, 63. Gwidden, drift of, 76. Nanvan, drift of, 76. Portscatho slates, 5, 6, 10, 18—20, 90 ; absence of elvans in, 62. Prah Sands, drift of, 77—81 ; elvan of, 64—66, 79 ; granite near, 48 ; slate of, 17. Praze tin mine, 102, 115. Precense, Wheal, 107. Preston, G. V. and H., on granite veins at Porthmeor, 45. Prestwich, Sjir J., on raised beaches and head, 145. Priest's Cove, granite and hornfels of, 13, 44, plate 6 ; drift of, 76. Prince George Mine, 107. Prosper and Mitchell United Mines, 130. United Mines, 130, 134. , Wheal, 99, 115, 130. Prospidnick, Wheal, 115, 130. Providence Mine, 11, 26, 47, 56, 87, 91, 95, 96, 98, 115, 116, 130. United Mines, 130. , Wheal, 130. Pryoe, W., on mines, 103, 134, 143. Psendomorphs after felspar, 45, 55 — 58. cordierite, 52. Puckering, 17. Puddling clay, 71. INDEX. 155 Punnett, H. M., on tin-ore, 116. Pyroxene, 34. Quartz crystals in elvan, 62, 65, 66. , palSBolithic implements of, 81. porphyry, 4, 9, 61—67. Radium in rooks of district, 60. Raised l)eaches, 3, 5, 75 - 77, 96, plate 4. Red River, 3 ; raised beach, near, 76 ; sandstone near, 19 ; sub- merged forest near, 82 ; towans of, 83. Eeeth Consols, 130. , Wheal, 97, 107, 116, 130. Reid, Mrs. B. M., on drift at Prah Sands, 79—81, 146. Relistian Mine, 96, 98, 116, 130, 134. Reskajeage, hone-stone of, 21. Retallack, elvan at, 64. Mine, 116, 130. Riblows Mine, 116. Rinsey, altered slate of, '40 ; granite of, 49. Road-metal, 34—36, 46, 47, 63, 64, 90. Rodney, Wheal, 99, 130. Roman mining, 86. Roscommon Cliff, lode in, 117. Rose and Penrose Mine, 116. Rqgemergy Cliffs, mine at, 113. Rosemorran, granite of, 60. Rosenbusch, Prof.H., on oassiterite, 52. Rosevidney, elvan at, 64. Rosewall Hill, 69. Mines, 92, 93, 96, 98, 116, 130, 134. Rosewarne, Mines at, 85, 96, 97, 116, 130, 134. Roseworthy, greenstone of, 34 ; spotted slate of, 22. Eospeath, slate of, 17. , Wheal, 102. Rov?e, Capt., on Balleswidden Mine, 100. Rundell, W. W., on granite masses in a lode, 95, 96. Runnel Stone, 14. Rutile, 22-24, 65. Ryeman, elvan of the, 63. Saint Agnes, tinstone pssudomorphs of, 55. Beacon, 5. Aubyn and Grylls Mine, 96, 99, 116, 130, 134. Clement's Isle, granite vein at, 42. Erth, elvans at, 63, 64 ; green- stone at, 10 ; mines in, 85, 101, 140 ; Pliocene of, 71—74, 78, 89. Valley, origin of, 69-72. Saint Gothian's Chapel, 83. Hilary, anticline near, 10 ; elvans of, 64; mines in, 85. 93, 96, 99, 140. District, mineral statis- tics of, 122. Ivns, building stone of, 47 ; drift of, 76 ; granite near, 89 ; greenstone of, 9, 34, 37, 39, 60, 90 ; mines near, 85—87, 93, 95, 96, 98—100, 103, 117, 140 ; raised beach of, 76 ; road metal of, 90 ; water supply, 92. Bay, 1, 2, 69 ; slate of, 18 ; towans of, 82, 83. Consols, 86, 86, 92, 93, 96, 98, 116, 117, 130. ■ — District, mineral statis- tics of, 122. Head, drift of, 76 ; green- stone and slate of, 11, 12 ; mines near; 114. Island, hornstone of, 26, 27. Wheal Allen, 130. Just, cliffs of, 44 ; granite of, 55 ; greenstone of, 9, 37, 91. Amalgamated Mine, 113, 130. ■ Consols, 131. District, mineral statis- tics of, 122 ; ore-deposits of, 44, 85, 86, 93, 95—100, 140, 141. United Mines, 101, 117, 131. ■ Loy, raised beach of, 77. Michael's Mount, absence of elvans at, 64 ; altered rocks of, 23; date of isolation of, 83, 84; Eocene near, 69 ; foreshore near, 16, 17 ; granite of, 40, 48 ; greisen of, 57, 59, 60. Salmon, H. 0., on boulders in lodes, 96; Saint Ives Consols, 116, 117. Sancreed, elvan at, 63 ; lodes near, 98 ; mines in, 113, 141. Sandberger, P., on lithia-micas, 51. Sand dunes, 19, 82, 83. Sarah, Wheal, 102. Schists, 15, 16, 34, 42. Schorl in elvans, 62, 67 ; in granite, 40, 41, 47, 48, 51. rock, 9, 14, 25, 26, 42, 44, 45, 54 — 58, 87, plate 6 ; as an orna- mental stone, 91. Scilly, connection of the granite with that of, 44; ice-scratched erratics in, 78. Scotland, phonolite of, 70. Scrivenor, J. B., on replacement of biotite by tourmaline, 56 ; on topaz in granite, 53. Sedgwick, Prof. A., on the Devonian System, 4, 143. 156 INDEX. Selective metamorphism, 8, 18, 19, 25. Sellan, elvan near, 63. Sennen, elvan at, 62, 90, 91 ; topaz at, 53. — — Cove, altered, rocks and granite of, 13, 14, 23, 24, 43 ; raised beach . of, 77. Serpentine, radium in, 60. Seven Years Cove, 12. Seymour, G., on Wheal Jennings, 107. Shark's Pin, 14. Shearing, 11, 13, 20, 29, 33, 41. Sheffield quarry, 89. Shell-sand in the raised-beach, 75, 76. Shepherds United Mine, 131. Shrinkage of granite, 61, 62. Sillimanite, 24, 25, 30. Silver, 85, 88, 100, 103, 107, 109, 116-118, 122, 134. Sisters, Wheal, 98, 128, 131. Sithney and Carnmeal Mine, 120. Wheal BuUer, 131. Slate altered by granite, 5, 7, 8, 11—14, 17, 20—26, 36, 43, 45, 53, plates 3, 5, 6 ; by greenstone, 11, 12, 15, 16, 20, 26—30; cleavage of, 7—9, 13, 16, 20, 61, 62 ; inclu- sions in granite, 24, 41, 43, 45, 53; radium in, 60. Slides, 88, 101. Smyth, Sir W. W., on mines, 102, 103, 108, 114. Snow-slopes, 81. Soil, 1 ; Palseolithic, 80. Soil-cap movement, 81. South Alfred Mine, 131. Carzise and Maria Mine, 131. Crenver Mine, 131. Great Work Mine, 131. Grylls Mine, 131. Pier, Penzance, elvan at, 63. Providence Mine, 98, 131. Speed Mine, 131. Tindene Mine, 131. Wheal Breage, 107. — Fortune, 131. Neptune, 131. Kose, 127. Speed, 121. Spearn Consols, 98, 131. Moor Mine, 131, 134. Wheal, 117. Speed, Wheal, 97, 99, 115, 131. Speedwell, Wheal, 99, 117, 131. Sphene, 34, 35, 37, 89. Spilites, 35. Spilosites, 26, 27. Spinel, 24. 25, 30, plate 5. Spotted slates, 8, 9, 11, 15, 19, 21— 24, 27, 76, plate 6. Statistics, ore, 122—132. Stennack, Wheal, 131. Stockworks, 97, 101. Stones, The, 19. Strain-slip cleavage, 7. Strap Eocks, raised beach of the, 75, 76. Strawberry, Wheal, 97, 99, 117, 131. Stream-tin, 77, 78, 81, 85. Strike of elvans, 62; of lodes, 98, 99; of slates, 9-11, 15,20. Strontium, 102. Strutt, Hon. E. J., on radium iu Cornish rocks, 60, 146. Submerged forests, 5, 81, 82. Sulphur ore, 122. Sydney Cove, drift near, 79 — 81. Mine, 17, 131. Godolphin Mine, 17, 131, 134. Symons, Brenton, geology of Corn- wall, 5. Synclines, 7, 10. Tater-du, granite of, 43, 50 ; green- stone of, 9, 14, 37 ; greisen of, 57 ; hornfels of, 23, 24, plate 6. Taylor, J., on mining, 143. Teall, Dr. J. J. H., on greenstones, 31 ; on metamorphio rocks, 20, 23, 25 ; on phonolite, 71 ; on petro- graphy, 145. Temperature of mines, 112. Tertiary deposits, 5, 68 —74. volcanic rocks, 70, 71. Thickness of strata, 6 — 10. Thomas, L., on Levant Mine, 108. Tindene Mine, 121, 131, 134. Tin-floors, 97, 103, 118. Tin-lodes, 44, 45, 57, 93—121 ; re- lation to the granite, 7, 8, 10, 20, 53, 54. Tin-mining, 85-87, 95. Tin-ore, statistics of, 112, 122—132. Tin-stone, 48, 52, 55—58, 66, 67, 87 ; in elvans, 66, 67 ; percentage workable, 97 ; pseudomorphs after felspar, 45, 55 —58. Toad's-eye tin, 117. Tolcarne, greenstone of, 15. Tolroy, elvan at, 64. Tolvaddon Mine, 131, 134. Tolvean Mine, 103. Tooke, A. W., on minerals, 144. Topaz, 38, 48, 52—59, 66, plate 6. Torbernite, 115. Tourmaline, 7, 9, 11, 22-25, 30, 32, 34, 37, 38, 40—42, 44, 47, 50—58, 65—67, 87, plate 6. schist, 26, 54. Towans, 82, 83. Towednack, mines in, 103, 106, 141. Trannack Mine, 95, 117. and Bosence Mine, 131. Ttawns, 99, 100, 104, 113. Treasure, Wheal, 13l INDEX. 157 Treasury, Wheal, 132. Trebarvah Mine, 99, 132, 134. Treen Copper Mine, 117. Tregassack, elvan at, 63. Tregellast, elvan at, 63. Tregembo Mine, 132, 134. TregiUia Stream Works, 132. Treglistian, greenstone at, 33. Tregonning Hill, 2, 69 ; granite of, 48. Tregurtha Downs Mine, 99, 117, 132, 134. Treloweth Mine, 98, 121, 132. Trelyon, mines near, 11, 92, 98, 113, 132. Tremayne, Wlieal, 98, 117, 132. Treinearne, granite veins of, 49 ; raisud beach of, 77. Tremethick, greenstone of, 14. TremoUte, 28. Trenorom, 69 ; mines near, 93, 122, 132. Trendrine Hill, 2. Trenow Consols, 99, 132. Trenwith, Wiieal, 86, 87, 92, 96, 117, 132. Tresoweshill, granite of, 49. Trevalgan, granite vein of, 45, 55, 91 ; mine at, 87. Trevarthian, lodes at, 99. Trevaskus Mine, 96, 100, 117, 132. Trevaylor, greenstone of, plate 5. Trevegean, lodes at, 96, 98. Trevean Cove, elvan at, 64. Trevelyan Mine, 99, 132. Treven Mine, 132, 134. Trevenna Mine, 132. Trevethoe Mine, 106, 132. Trevorian, slates near, 18. Trewavas, altered rocks of, 23, 26 ; granite of, 17, 40, 48, 49, 53, 55 ; raised beaches near, 75; tour- maline at, 25. Mine, 118, 132. Trewellard, tin-floors at, 97. Trewidden Bh\, 97, 118. Trinity House, specimens supplied by, 14. Trink Hill, 69. Trungle, Wheal, 134. Truro, anticline of, 10 ; green- stones of, 39. Truthwall, lodes at, 99. Tungsten, 46, 48, 54, 100, 107, 109, 115, 116. Unity, Wheal, 118, 132, 134. Uny Lelant, mines in, 141, 142. Upton Towans, 18, 19, 83. Uralite, 32, 39. Uranium, 48, 54, 85—87, 106, 114—117. Ussher, W. A. B., on drift deposits, 5. 145. Valleys, Eocene, 69—71. Values of minerals, 122—132. Variegated slates, 5. Veriton, elvan at, 64. Wheal, 134. Verrant, Wheal, 132. Veryan Beds, 5, 6. Violet Seton Mine, 118, 132, 134. Virgin, Wheal, 99, 113, 132. Volcanic tuffs, 28. Vor, Wheal, 93, 97, 99, 115. Vorlas, chalk-flints at, 68, 69. Vyvian Mine, 98. Water in mines, 101, 102, 104, 106, 112, 113, 116, 117. Water supply, 91, 92. "W^eeth Mine, 133. Wellington Mines, 133. , sarcophagus of the Duke of, 56. West Alfred Mine, 98, 133. Bostraze Mine, 133. Carzise Mine, 99, 133. Ding Dong Mine, 133. Dolooath Mine, 134. Godolphin Mine, 99, 107, 118, 133. Great Work Mine, 133. — — Grylls Mine, 133. ■ Poldice Mine, 106. Providence Mine, 133. Rosewariie Mine, 96, 134. Koskear Mine, 133, 134. Tolvaddon Mine, 118. Tremayne Mine, 133. Wheal Abraham, 99, 104. Alfred, 133. Darlington, 99, 118. Fortune, 133. Lucy, 133. Mary, 133, 134. Prosper, 133. Seton, 118. Treasury, 98, 133. Trevelyan, 133. Western Green, 83 ; submerged forest of, 82. Wheal. See name of mine. Wherry Mine, 63, 86—88, 118, 133; ■ Rock, submerged forest near, 82. Town, elvan at, 63. Whetstone, 46. Whitaker, W., bibliography by, 144. White, Major, on Levant, 108. WhitesandBay,elvan at, 62; granite of, 43, 44; mines of, 122; raised beach of, 77 ; towans of, 82, 83. Whitley, N., on glacial action, 145. Wicca Pool, drift near, 76 ; granite veins of, 45. 158 INDEX. Widden, Wheal, 102, 133. Wilkinson, B. S. N., on elvans, 64, 65 ; granite veins, 43 ; green- stones, 10 ; My lor slates, 12. Wolf Rook, 1, 2, 70, 71. Wolfram, 46, 48, 54, 100, 107, 109, 115, 116. Wood, S. v., on the Pliocene of St. Erth, 71, 145. Wood-tin. 106. Worvas Downs Mine, 121, 133. Yankee Boy Mine, 133. Goose, 111. Zawn Bunny, 111. Za'wns, 12, 13. Zennor, andalusite-bearing granite of, 53 ; granite of, 41, 45, 46, 89 ; granite veins at, 48 ; junction of slate and granite at, 12 ; mines in, 94, 142. Zeolites, 38. Zincblende, 39, 48, 54, 96, 100, 103, 104, 106, 107, 117, 118, 134. Zinc-ore, statistics of, 122. Zircon, 24, 50—53, 56, 57, 66. Zirkel, Prof., on phonolit© of Wolf Rock, 71. Zoned felspars, 50. Plate I. View of the south side of the Land's End. _ Exhibiting the castellated appearance of the granite clifif, and the weathering of the upper part into isolated stacks or earns. The height of the cliff on the right is about 150 feet ; but the waves and wind during storms have removed the soil up to the highest point here shown. The cliff consists in the main of coarsely porphyritic granite ; but in several places the photo- graph shows irregular veins of finer-grained granite. Plate II. Crag below Crowns Mine, Botallack Head. Shows, on a joint-face, greenstone and slate, sheared into thin alternating laminae, and afterwards baked and altered into hornfels by the intrusion of the granite, here about 200 yards away. Though weathering brings out the alternation, the rock is very tough, and breaks with a conchoidal or splintery fracture in any direction. The fractured surface shows alternate stripes of dark and light green, sometimes brecciated. The pale irregu- lar blotches are lichen, and not rock-structures. ti, "« I »^ ^ Plate III. Granite Veins in Killas, Forthmeor. A vertical vein of coarse porphyritic granite intersects and shifts a slightly older vein or iine-grained non-porphyritic granite. The surrounding rock is fine-grained Mylor slate, with a little sheared greenstone (not distinguishable in the photo- graph). The slate is altered into knotted hornfels, and a few yards from this spot yields small perfect garnets ; these are readily seen on the weathered surface of a narrow band, which was probably more calcareous than the rest of the rock. The main mass of the granite is seen in the same cove. so I o Cb Plate IV. Raised Beach in Penlee Quarry, near Mousehole. Rock-platform and sea- worn clifif of greenstone, against which is banked coarse, well-rounded shingle, covered by a wash of ' head ' from the slope above. The platform is 65 feet above Ordnance datum, and this is the highest Pleistocene beach yet found in Cornwall. 1^ o W H P o 1^ M ■< Iz; « << O* M u:i |Zi ei Ph W o a m Plate V. Photomicrographs (2). FIG. 1.— Neg. No. 310 M. Slide No. B. 3i58. Magniaed 10 diameters. Ordinary Light. Andalusile-Hornfels. Cape Cornwall (S. Side). This photograph shows large crystals of andalusite, with dark enclosures, lying in a matrix consisting of quartz and biotite, with iron oxides, etc., and indistinctly spotted with pale spots consisting of quartz, chlorite, and rnuscovite. FIG. 2— Neg. No. 321 M. Slide No. E. 4277, Magniaed 23 diameters. Ordinary Light. Hornfds. Enclosure in granite, Latnorna. The photograph shows crystals of biotite, andalu- site, spinel, and iron oxides, in a clear matrix of quartz and cordierite. FIG, 3. -Neg. No. 325 M. Slide No. E. 3718. Magniaed 23 diameters. X. Nicols. Greenstone. N. entrance to Penzance Harbour. Example of a porphyritic greenstone. The phenocrysts, which are of plagioclase felspar, lie in a matrix of weathered felspar, chlorite, leucoxene, etc. FIG. 4.— Neg. No. 324 M. Slide No. B. 3488. Magnified 10 diameters. Ordinary Light. GreenstoTie. 200 yards E. of Chymorvah, Marazion. Example of a greenstone, with remains ot ophitic structure. The augite is all converted into secondary hornblende, and the felspar is much decomposed. There are also scattered grains of ilmenite which are weathering to leucoxene. FIG. 5.— Ne.g. No. 318 M. Slide No. B. 3724. Magnified 23 diameters. Ordinary Light. Hornfels. Botallack. The photograph shows slender, nearly colourless, needles of amphibole, in bands and stellate groups. These lie in a matrix which is composed partly of felspar, partly of cordierite. The rock is full of black grains of magnetite arranged in bands. PIG. 6.— Neg. No. 322 M. Slide No. E. 3427. Magnified 10 diameters. Ordinary Light. Spotted Greenntone. Trevaylor Quarry, Chyandour. Rounded spots, consisting of dark-green horn- blende surrounded by pale-yellow augite, lie in a fine, highly sheared matrix of felspar, leucoxene, iron oxides, augite, etc. GeolqcjlJ of Ihr hnm^ fyn4. Plate llOTOMICROGRAPHS, Photomicrographs. Plate VI. FIG. 1.- Neg. No. 335 M. Slide No. B. 4016. Magnified 10 diameters. Ordinary Light. Granite. Newmill. The photograph shows broad areas of clear quartz, partly idiomorphic, and of highly turbid felspar (perthite). A longitudinal section of a pinite pseudomorph (consisting of muscovite and chlorite) after cordierite exhibits the window-bar structure usual in these ag|?regates. Muscovite, and chlorite after biotite are also present in the field. FIG. 2.— Neg. No. 334 M. Slide No. E. 3519. Magnified 30 diameters. Ordinary Light. Granite. 8 chains N.W. of Knill's Monument. This photograph is taken from a section of the finer variety of Land's End granite. In the upper part of the field^ there is a rough colourless grain of topaz with good cleavage. Below there is a patch consisting of chlorite, biotite, and small pleochroic crystals of andalusite. Two small andalusites lie near the centre of the field. The rest is clear quartz and turbid felspar. FIG. 3.— Neg. No. 329 M. Slide No. E. 3800. Magnified 17 diameters. Ordinary Light. EUan Dyke. Bezurrel, Gwinear. This shows porphyritic quartz, but all the felspar has been converted into a mixture of muscovite and quartz by the greisenifig action of pneumatolytic vapours. The dark patches are chlorite. FIG. 4.— Neg. No. 331 M. Slide No. E. 3473. Magnified 17 diameters. Ordinary Light. Schorl Rock. Vein in Granite, Mousehole. This consists of a granular matrix of quartz, with brown, yellow and blue tourmaline. A few grains ot cloudy felspar also appear in the section. The tourmaline is usually parti-coloured or zonal. FIG. 5.— Neg. No. 313 M. Slide No. E. 3459. Magnified 12 diameters. Ordinary Light. Andalusite-HornfeU (Spotted). Priest's Cove, Cape Cornwall. The spots, which are pale, consist mostly of muscovite and chlorite. The matrix between is a mixture of quartz and dark-brown biotite. In this matrix, and independently of the spots, small crystals of andalusite (not clearly shown in the photograph) are developing. FIG. 6.— Neg. No. 312 M. Slide No. E. 3985. Magnified 23 diameters. Ordinary Light. Biotite- Horn/els. Tater-du. This rock consists of biotite, quartz, a little felspar, tourmaline, and iron oxides, zircon, etc. It has been intensely altered, but is free from spots. (ieoloyf/ of the Land's l£ad Plate r,. 0£N£BAL H£MOIBS. SUMMARY OF PEOGEESS of the GEOLOGICAL SUEVEY for 1897, 1898, 1899, 1900, 1901, 1902, 1903, 1901, 1905 and 190S. Each 1<. PLIOCENE DEPOSITS of BEITAIJT. By C. EBID. Bs. id. CBBTACEOUS UOCES OB' BKITAIN.— Vol. I. GAULT AND UPPER GEBENSAND pP ENGLAND. 9». Vol. IL LOWER AND MIDDLE CHALK. 10». VoL in. UPPER CHALK. 10s. By A. J. JCKKS-BEOWNK and W. HiLt. JURASSIC EOCZS OF BRITAIN.— Vol. I. YORKSHIRE, 8». 6d. Vol. II. YORKSHIRE, Fossils. 12». Bjr C. FOX-Stranqways. Vol. ni. LIAS OF ENGLAND (Yorkshire excepted). Is. U. By H. B. WOODWARO. Vol. IV. The Lower Oolitic Rocks of England. 10«. By H. B. WOODWABD. Vol. V. The Middle and Uppw Oolitic Rocks of England. 7a. 6i{. By H. B. WooDWASD. BRITISH ORGANIC REMAINS. 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