Law son ~| 

 PalacheJ 



The Berkeley Hills. 



443 



discharging into the existing sea, and at the same time a shoaling' 

 of the sea, inasmuch as conglomerates can only accumulate in 

 water of very limited depth. Conglomerates are very commonly 

 formed in broad sheets by the action of a sea encroaching upon a 

 land area, the waves working over the fragments detached from the 

 surface over which the sea is transgressing. This, however, can 

 not be the explanation in the case of the conglomerates with 

 which we are here concerned; for, although the conglomerate 

 occurs characteristically at this horizon* in the Coast Ranges, in 

 extensive strata, yet the action of the sea upon the soft Knoxville 

 shales could produce no such polygenous conglomerate as the one 

 in question. The source of the conglomerates was, therefore, 

 clearly beyond the limits occupied by the underlying shales. But 

 the shales themselves were also derived from beyond these limits, 

 and the change in the character of the materials supplied by the 

 streams could only have been due to a sharp orogenic deformation 

 which strongly accentuated the erosive and transporting power of 

 the streams. 



This acute movement was followed by a long-continued, steady, 

 and gentle subsidence of the sea bottom; for, resting upon these 

 shallow-water conglomerates, is a great volume of sandstones with 

 quite subordinate intercalations of shale. These comprise the 

 Chico division of the Cretaceous. The sandstones are for the most 

 part heavily bedded, indicating uniform conditions of deposition, 

 and they are uniformly of medium fine grain. The entire record 

 of Chico sedimentation is not revealed in our field, since the section 

 of these rocks terminates at a surface of erosion. Nor is the 

 attitude of the beds sufficiently exposed to indicate the degree of 

 deformation to which the Chico had been subjected prior to this 

 erosion. In the emergence into the zone of this erosion the region 

 was very probably deformed, but this defoi'mation does not seem to 

 have been acute, since the strike of the beds is in general accord 

 with the unconformably overlying strata. 



Reposing upon the erosion surface are beds of the Monterey 

 Miocene, and it is from this fact chiefly that we know that it is an 

 erosion surface; for, as has been already stated, rocks of Eocene 



* Cf. Diller and Stanton, Bull., G. S. A., Vol. 5, pp. 435-464. 



