Clark: The San Lorenzo Series of Middle California 79 



with the hasal sandstone of the San Ramon formation, the shale having 

 been eroded away. 



Pholad borings were found in abundance on the north side of the 

 creek. The basal beds of the San Ramon formation, at this locality, 

 consist of a rather coarse, grey sandstone, in places finely conglom- 

 eratic, together with communuted shells scattered through it. 



Water-worn coal pebbles of considerable size and abundance are 

 found in the lower sandstones of the San Ramon at this locality. Tt 

 seems very probable that these pebbles were derived from the Tejon, 

 which is the only horizon in this general region known to contain coal 

 in any considerable abundance. The presence of these coal pebbles, 

 therefore, furnishes additional evidence for the unconformity between 

 the San Ramon formation and the Tejon. 



Lithology of Lower Monterey (Miocene). — Only one well-defined 

 shale member is present in this section of the "Monterey Group"; 

 this is about one hundred feet above the base. The beds below this 

 shale represent shallow-water deposits, consisting of coarse gray sand- 

 stone, in which cross-bedding is common, together with lenses of con- 

 glomerate and shale. 



The line of contact between the basal beds of the Monterey 

 (Sobrante formation as redefined) and the San Ramon formation is 

 marked by conglomerate and coarse, massive, gray sandstone. The 

 conglomerate is lenticular and, in some localities, has a thickness of 

 from ten to fifteen feet ; in other localities it is entirely absent. The 

 boulders and pebbles found in it were derived from many sources, 

 both igneous and sedimentary. 



Evidence for Stratigraphic Break. — The evidence in this section 

 for a stratigraphic break between the Monterey beds and those of 

 the San Ramon formation is as follows : First, it is suggested by 

 lithology ; conglomerates and coarse sandstone occur along a line of 

 contact below which there is a sudden change to a fine sandstone; 

 second, this line of contact is irregular; the irregularities, in some 

 localities, are as much as three to four feet and often are quite sharp ; 

 third, fossiliferous boulders which contain characteristic species of the 

 Agasoma gravidum beds are found in the conglomerates at the base 

 of the Area montereyana zone. At some localities these boulders are 

 so abundant that one must be careful in collecting from the matrix 

 of the conglomerate, lest he get a mixture of the upper and lower 

 faunas. The writer has collected over ten species of the Agasoma 

 gravidnm fauna from these boulders and undoubtedly a much larger 



