1.AWSON T 



palach eJ 



The Berkeley Hills. 



355 



removed from ordinary terrigenous sedimentation, and yet their 

 stratified upbuilding in thin layers of hard chert alternating regu- 

 larly with partings of a peculiar shale, points clearly to a rhyth- 

 mical oscillation of the conditions of accumulation, and the signifi- 

 cance of the rhythm is as yet an unsolved problem.* These 

 rocks may be observed on the lower slopes of the Berkeley Hills, 

 north of Berkeley, and to still better advantage in the Piedmont 

 district of Oakland, particularly on the ridge to the north of 

 Oakland Park. 



Another interesting formation of the Franciscan series is a 

 compact light gray limestone, with which are generally intercalated 

 thin lenses and sheets of dark chert. On a smooth surface of this 

 limestone there usually may be seen small hyaline spots resembling 

 somewhat the fossil radiolaria in the red cherts just described, but 

 the)' are not so round. These are also fossils, but of an entirely 

 different order from the radiolaria. They are the casts of cham- 

 bered calcareous shells of various species of foraminifera, and the 

 rock is therefore known as a foraminiferal limestone. This lime- 

 stone is unfortunately not exposed along the base of the Berkeley 

 Hills, and the nearest outcrops at which its acquaintance may be 

 cultivated are on the San Francisco Peninsula and in Marin 

 County, near Tomales Bay. There are, of course, associated with 

 the sandstones of the Franciscan series also shales and conglom- 

 erates, and the former may be seen well exposed in some of the 

 road cuttings in the hills back of Oakland. At the mouth ot 

 Strawberry Canon in the creek bed the shales crop out for a few 

 yards, but they have been intensely sheared and crumpled so that 

 they have rather the character of crumpled phyllites than ordinary 

 shales. The)" are, in respect of their deformation, in strong con- 

 trast with the little disturbed shales of the Knoxville series, which, 

 resting upon them, are exposed a little above on the cutting of the 

 canon road. 



*For an account of the occurrence of radiolarian cherts in the Bay region, 

 see Ransome on The Geology of Angel Island, Bull. Dept. Geol. Univ. Cal., 

 Vol. i, No. 7. Also Lawson, Sketch of the Geology of the San Francisco 

 Peninsula, 15th Ann. Rpt., U. S. G. S. 



