UC BERKELEY MASTER NEGATIVE STORAGE NUMBER 03-67.51 (National version of master negative storage number: CU SN03067.51) MICROFILMED 2003 UNIVERSITY OF CALIFORNIA AT BERKELEY LIBRARY PHOTOGRAPHIC SERVICE REPRODUCTION AVAILABLE THROUGH INTERLIBRARY LOAN OFFICE MAIN LIBRARY UNIVERSITY OF CALIFORNIA BERKELEY, CA 94720-6000 COPYRIGHT The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted materials including foreign works under certain conditions. In addition, the United States extends protection to foreign works by means of various international conventions, bilateral agreements, and proclamations. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. University of California at Berkeley reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. Sheffield, E. S. A cross-section of the Oakland hills 1904 BIBLIOGRAPHIC RECORD TARGET University of California at Berkeley Library Master negative storage number: 03-67.51 (national version of the master negative storage number: CU SN03067.51) GLADIS NUMBER: 184777521G FORMAT : BK AD:990922/FZB LEVEL:b BLT:am DCF:a CSC:d MOD: EL: 7 UD: 030623 /MAP CP: cau L:eng INT: GPC: BIO: FIC: CON: ARCV: PC: PD:1904/ REP: CPI: FSI: IC: IX: CUScCU 040 090 100 245 260 300 502 610 690 700 1 SbDISS.SHEFFIELD.GEOL 1904 Sheffield, E. S. 12 A cross-section of the Oakland hills. 20 Scl1904 8 leaves :Sbcol. maps ;$c29 cm. Thesis (B.S. in Geology) -University of California, Berkeley, May 1904. University of California, Berkeley.S$bDept. of Geology and GeophysicsSxDissertations. Dissertations, Academic$xUCBS$xGeologyS$y1901-1910. Lombardi, M. E. Microfilmed by University of California Library Photographic Service, Berkeley, CA FILMED AND PROCESSED BY LIBRARY PHOTOGRAPHIC SERVICE, UNIVERSITY OF CALIFORNIA, BERKELEY, 94720 DATE: 7/03 REDUCTION: 10 X PM-1 3%."x4"” PHOTOGRAPHIC MICROCOPY TARGET NBS 1010a ANSI/ISO #2 EQUIVALENT ug £2 2. 2 6 Ema » Lo SERIO, “w =1t ry THPFTERERErer 5/1 6] a" =} ny 4 hs LIE LOL lS hdd hd hl lin A CROSS-SECTION of the OAKLAND HILLS, Thesis submitted by E. 3S, Sheffield and M., EB. Lombardi. May, 1904. LIBRARY COPY DXssS SHEFFIELD GEOL oy Ha The section examingd lies east of Blair Pask, Oakland, in a line approximately north-east by cast for esven miles, It may be considered a osntral esction of the range of hills to the north-east of Oakland, These are a southward contimmation of the Berkeley | hills, and the main features of geological sequence and structire | | are conmonh $0 both ranges, | The object of investigation was to gather material for a eroso~-soctioned map along an arbitrary line, No attempt was made to follow the contacts of the various formations, or to map the areas of their exposure further than was thought necessary for the understanding of their geological sequence, The line chosen crosses the hills at right angles to the pro- nounced longitudinal axis of the range. The section ghows clearly a normal syncline, It also shows that the axis of the fold is not horizontal at this particular place. The center of the fold is at a point north of Roundtop ~the highest point on the section- and the depression seams t0 be cup-shaped. The folding which produced the synelinal structure occurred after the deposition of all the formation now represented. It occasioned a mumber of faults and slips, most of which run parallel de BE to the strike of the strata. The drainage of the hills is entirely subsequental. Geological Structures. “Q=0=0— The base of the series which compose these hills is Franciscan sandstone. It is a hard, siliceous stone, in characteristic mass- ive beds, and full of intrusions of green-stone. It lies almost flat, dipping eight degrees towards the north-east. Near the west end of the line is a small intrusion of green-stone, much al- tered. A bed of radiclarian chert eighty feet thick lies conform- ably in the sandstone. Above the Francisean, and lying on it unconformably, lies a band of soft shale, fifty feet wide. These are the Knoxville shales and are referred to the Shasta-Chiee. Above them is rep- resented the Knexville conglomerate, but in a narrow layer compared to other exposures. The material is very coarse. No evidence to the contrary being obtainable, they were assumed conformable with the underlying shale and the overlying sandstone and shale. The Knoxville shales are here cut by a twenty foot dyke of Serpentine, altered to a large extent to a quicksilver rock. | Above the conglomerate lies three thousand feet of soft sand- -3- gtone and shale, containing beds of hard blue limestone. This is the dpper part of a Shasta-Ohico series. COonformably on them and forming the first hijh ridge encountered, lie the Monterey chert and shale, This is a persistent ridge, a contimuation of Skyline Ridge in the Berkeley hills. The formation here is about two thousand feet thick and shows the highest inclination found on the sectioh, It is characterised by bold out-crops and thin soil, and by its well known chert and shale sequence; 2-1/2 inches chert to 1/2 inch shale. Gonformably on the Monterey, lies a bed of fresh water con- glomerates, at this point eighteen hundred feet thick. This is the Orindan formation. Lenses of sandstone occur in it and the conglomerates are in places cemented, showing good out-erop. But its peneral soft character have made its area a drainage basin to the north and south. These Orindan conglomerates are the lowest formation found on the east side of the syneline within the limibs studied. On the east, their thickness is very much greater, and beds of coarse sandstone more prominent. A hard sandstone bed one hundred and fifty feet thick forms the crest of Mulholland hill but its longitudinal extent is limited to about a mile. Twenty- five hundred feet lower down to the east of this sandstone bed, is a fifty foot bed of very hard cemented material, forming a bold bluff, This marked difference in the thickness of the Orindan eonglomerate indicates its deposition from the east, and a thinning nm out towards the west away from the source of the material. On these conglomerates lie the lava flows which form the cap of Roundtop. They occurred in two flows, with a time interval between, shown by a ten foot bed of agglomerate. The lower flow is only about twenty feet thick at the largest exposure measuved. It 1s an Andesite of fine, even strusture, characterized by amigules of chalcedony. The upper flow gives evidence of being much thick- er. Two hundred feet is measurable but as this forms the top of the range where it is best exposed, there is no means of telling how much has been eroded away. This flow is basalt, much weather- ed and showing several facies. These lavas cap the rugged line of ridges east of Roundtop. They dip down toward the north and east, and pass under the next formation, the Siestan, but do not re-appear on the other side of the syncline, owing to a fault of considerable flow. The Siestan formation, evidently an old lake basin, is here estimated to be one hundred and fifty feet thick, and is composed of brown and gray shale; fine grained, gray sandstone; conglomerates to a limited extent; white breccia; and a characteristic hard, blue clay. It is a very soft formation and has been eroded into a broad valley which can be traced for miles along its strike, Detached pieces of white limestone were found, showing mumerous fossil shells which fix the formation as fresh-water. Resting on the lake bed are the remains of a lava flow which is the latest formation found on the section studied. The lower part of the flow is of the character of breccia, and contains inclusions of pre-existing sedimentary rock. It is badly weathered but seems to have been andesidiec. The main part of the flow is basalt. The flow is three hundred and fifty feet thiek here, and is nearly horizontal, being about in the axis of the fold. It forms,by virtue of its hardness, a hill called Twin Peaks, rising out of the valleys eroded from the soft fresh-water formation and the Orindan conglomerates. There is mo evidence obtainable as to the conformity of this flow to the lake bed, but the presence of breccia structure at its base seems t0 indicate that the lava was poured out into an existing lake basin. The section is traversed by three faults of gome magnitude. The first occurs in the radielarian cherts, forming the ridge Just east of Blair Park. They have been opened for guarrying purposes, disclosing a north and south fault plain which has raised the coun- try west of the plain about seventy feet, and exposed the base of the chert. They rest at this point on a soft, gray rock whieh is evidently of velecanic origin, tut entirely decomposed and unrecog- nizable. There is no evidence of intrusion here, Where the line comes to the upper end of the Monterey chert, a fault of considerable magnitude running at a small angle to the strike of the chert bed, seems to oross from the Monterey into the overlying Orindan conglomerates. The country to the west of the fault plain has been dropped several hundred feet, and the east —, fo side eroded down. To the west of the plain, the north-east dip of the chert beds show conformity with the underlying shale and sandstones of the Shasta~Chico, whereas the higher part of the ved still existing to the east of the fault dips back under the Orindan conglomerates, and is conformable with them. In the valley bottom between Twin Peaks and Mulholland hill, the Siestan lake beds are found in contact with the re-appearing Orindan conglom@rates. This is best explained by the existence of a fault which raised the country to the east, The formations covering the conglomerates- Roundtop lava flows~ have since been eroded away, and the sequence found on the west of the axis of the fold apparently broken. The three faults described strike approximately parallel to the axis of the syncline., The two toward the west end of the line point to a letting down of the country between them, The Monterey cherts seem especially susceptible to faulting. i ¢ a PETROLOGY. at ad Lower flow of Roundtop lava: This is an amigdaloidal andesite of fine, even structure. It is very well preserved and very hard. Small thenocerysts of augite are very abundant. Upper flow of Roundtop lava: This is a fine, even-grained basalt. It weathers mich more easily than the andesite. The augite is abundant and in two generationg. The olivine is in small orystals and not abundant. Twin Peak Basalt: This basalt shows a more glassy ground mass and larger thenoerysts than ‘that above described. The thenocrysts are basic plagioclais and large crystals of augite, with wome olivine. Serpentine and Quicksilver Rock: The serpentine is evidently an It contains the remains alteration product of a basie intrusive. of augite and hornblend erystals, and the mesh structure of olivine. Co About three-fourths of the serpentine is altered to quicksilver gore 10 Tol Tew ~~ jrock. This is a hard mass of dolomite, calcite, and silica. I 1t contains a great deal of iron in the shape of magnatite grains outside nove om | * "fand limonite stains, 10 etuyroomens Lied shorofl 10 volt weal : a i rom dou eTedisew ows nt brs Sabo .insbruws fon 1] E] at y it i adntup bre enlineds 16 $oubory MOLIST X QV 2 Q YH S Q NN A\ Contra Costa 8 AH/armedo Geo/og/ca/ Sec tron Through Oakland /71//s Delterrrirzed Ly IE Lombards ond £SSher re/d Scole /rinch = ’7 bofeef Rovnd Top Twn Feaks ’Mulbollond Hrl/ Sand sto ard Shales Monrtery Shales Chert oly sha/ es ad Bosic intrusive Radralariorn Serpen Firme fimoxvelle Stale Corrg/omerote Sor chert 4 and Qu. S1lver rock Lower Berkeleyan Orss7lan Round 7op Lavaes Freshwoler Sard stone Arcesy te Agglomerote Basq/t Freshwoleyr Conglesmeretes rocks; sholes clays orrd [1 me SF, on AT] lg 2 mma, HELE X Q $ Q “ 2 Q NN Geo/og/ca/ Sec ror Through Oakland /71//s Delterrrrsr7ed Ly STE Lombards ond £8 Sher re/d Scole /rinch = 176 ofee¥ —_—. Contra Costa Alar edo Bou dary ! | Round Top Twin Feaks AA ra TR CLE? ila PN NMulbollond Hill Shasta Chico A TT] == — Bosic mmtrvsive Radralariors Serpentime fimovville Stale Corrg form erole Soma s tone chert and ord Qh. Silver rock Sha/e Lower Berkreleyarn 7 Pe Ors#7clanr Round Jop Lavas Jes tor 7 TN Shales Chert olnd Freshwoler Sard stone Arcesy te Agglomerote Basq/t Freshwoley sho / Conglormeretes rocks, shaoles | clays ord /1 me SE, A PEPER Erp ECE AL gg gg st, #1, g/t alt ie ot 6 [8 |z 9, & le, 2, [t™ ies Hh 6 END OF TITLE