LAWSON ~] 

 I'ALAI il i- J 



The Berkeley Hills. 



367 



iron, and, like most of the beds found in the Monterey series 

 throughout the Coast Ranges, are also magnesian. They are 

 usually less persistent along their strike than the sandstone beds 

 above described, and are to be regarded rather as discrete lenses 

 than continuous beds. The limestones and sandstones together 

 are estimated to make up less than five per cent of the entire thick- 

 ness of the section. 



The rocks of the Monterey series as represented in this section 

 must, from the foregoing description, be regarded as a peculiar 

 formation which has been laid down under conditions which differed 

 radically from those which have obtained in ordinary basins of 

 sedimentary accumulation. In the shales which interleave the 

 chert beds have been found certain fossil molluscs, such as Pecten 

 peckhami, which are characteristic of the Monterey series and 

 which establish the marine origin of the formation as a whole. 

 The cherts ordinarily show no fossil remains, but in thin sections of 

 a few specimens microscopic forms of minute organisms have been 

 detected imbedded in the chert matrix, and these, of course, sug- 

 gest that the silica of the cherts was in part at least derived from 

 organic sources, but the general problem of the origin of the 

 formation, which is presented by its remarkable composition, the 

 mysterious rhythm of its stratification, and its intercalation of 

 peculiar sandstones and limestones — this genetic problem is one 

 whose discussion must for the present be deferred. 



Monterey Only Partially Represented. — It should be observed 

 before leaving this part of our subject that this formation, as ex- 

 posed in Skyline Ridge, does not represent the entire Monterey 

 series. The series in Contra Costa County, only a few miles to the 

 eastward, is made up of an alternation of four fossiliferous sand- 

 stone formations and three formations of "bituminous shale," 

 aggregating in all several thousand feet in thickness. Considera- 

 tions which need not here be stated lead to the conclusion that the 

 formation with which we have now to deal is the lowest of the 

 three "bituminous shale" formations, or the second of the seven- 

 fold series. 



Having now become somewhat familiar with the petrographic 

 character of the formation, we may turn our attention to its struc- 



