University of California. 



[Vol. 2. 



the western flank of the Berkeley Hills north of Berkeley, it is 

 clear that before the formation of the Campan trough the Berke- 

 leyan syncline had been so reduced by erosion that it had feath- 

 ered out, somewhere between the line of the Canon fault and the 

 present front of the Berkeley Hills, where we find the Campan 

 beds resting directly upon the sandstones of the Shasta-Chico 

 series. In this fact we have a measure of the unconformity. Not 

 only was the time interval between the Berkeleyan and the Campan 

 sufficient for the great orogenic deformation exhibited by the 

 Berkeleyan syncline, but also for the degradation of that syncline, 

 so that the Campan trough was established across the worn edges 

 of the northwest end of the tapering, canoe-shaped structure. We 

 may, therefore, safely conclude from these considerations that the 

 Campan trough, or basin of accumulation, was long subsequent to 

 the Berkeleyan epoch, and that the interval between the two 

 epochs was probably not less important in the geological evolution 

 of the Coast Ranges than those epochs themselves, although it is 

 not represented in this region by strata. 



It is not clear whether the Campan basin was originally a 

 diastrophic trough or merely an ordinary valley of erosion which 

 had become dammed, owing to some geological accident, such as 

 its partial occupation by lava. But inasmuch as the Cafion fault 

 clearly made it a diastrophic trough, it is a fair hypothesis to sup- 

 pose that the forces which culminated in that dislocation had pre- 

 viously been active, and that the original depression was due to 

 local deformation. 



Deformation of Campan and Berkeleyan Contrasted. — The 

 contrast in the character of the deformation of the Berkeleyan 

 and Campan rocks is interesting. The Campan basin, like the 

 Berkeleyan, has been folded synclinally, but the flexure is much 

 more gentle. On the other hand, the Campan basin is much more 

 broken by faults than is the Berkeleyan, and it is probable that 

 most, if not all, of the faulting of the region took place either 

 during the Campan epoch or subsequent to it. Inasmuch as the 

 rocks occupying the two basins are very similar, we must ascribe 

 the difference in the condition of deformation to some other than 

 a petrographical cause. One general difference in the character of 



