446 



University of California. 



[Vol. 2. 



nothing to the probability of rhythmical supply of silica from vents 

 connected with this volcanic activity. 



It must be admitted, therefore, that we have not at present any 

 reasonable working hypothesis explanatory of the rhythm of sedi- 

 mentation of these remarkable strata. It may, however, be pointed 

 out that the rhythm referred to is rather local in its development, 

 since we have much greater volumes of the bituminous shales in 

 other parts of the Coast Ranges in which such peculiar bedding is 

 not apparent. The local development of the rhythmical sedimen- 

 tation appears to be connected with the proximity of this portion 

 of the basin to the land, and to be due to the rhythmical interrup- 

 tion of a continuous deposition of silica by influxes of fine terrig- 

 enous silts. If this be a fact, then the explanation of the rhythm 

 in sedimentation must be sought for in the variation of the condi- 

 tions on the surface of the land, whereby periods of discharge of 

 fine sediments into the sea alternated with periods of little or no 

 discharge. Under such conditions the accumulation of silica, in 

 the outer portions of the sea, removed from the seat of terrigenous 

 deposition, would proceed uninterruptedly, and no rhythm would 

 be apparent in the deposit. This consideration, it may be pointed 

 out, favors the first possible explanation mentioned, viz., an annual 

 rotation of conditions. But the problem is here regarded as an 

 entirely open one, which invites earnest investigation. 



In portions of the Coast Ranges only a very few miles distant 

 from the Berkeley Hills to the eastward there are several other 

 formations of the Monterey series aggregating in volume 4,700 feet 

 reposing upon this particular formation of cherts and shales. These 

 higher formations undoubtedly originally covered the region of 

 the Berkeley Hills, but were removed by erosion; after deformation, 

 before the development of the basin in which the Lower Berke- 

 leyan beds were deposited. We have, therefore, at the summit of 

 this formation of cherts and shales an important hiatus in the 

 history of sedimentation of the Coast Ranges. At the close of 

 Monterey time orogenic movements affected this region in common 

 with other portions of the Coast Ranges. The strata were folded, 

 broken, and elevated above sea -level into the zone of erosion. 



After the Monterey rocks had been in places partly removed, 



