12 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



IV. Stratigraphy of the Cretaceous. 

 I. Basement Complex. 



In the foregoing review it was stated that the Cretaceous 

 deposits of the West Coast are found, for the most part, 

 occupying the present valleys, which are the results of a 

 pre-Cretaceous folding, not yet obliterated. This fact is 

 worthy of being further emphasized, since it is not yet suf- 

 ficiently recognized. It can be shown in many ways that 

 this distribution of the Cretaceous rocks is not to be attrib- 

 uted to erosion, but it represents the original conditions of 

 Cretaceous and pre-Cretaceous physiography. 



It has already been shown by Diller and Stanton (1894), 

 by J. P. Smith (1894), ^"^ others, that the unconformity 

 between the Knoxville beds and those of the older Mesozoic 

 and pre-Mesozoic ages represents an uplift and period of 

 land erosion prior to the Cretaceous deposition. 



Dr. Smith places this period of folding, metamorphism, 

 and erosion at the close of the Mariposa epoch, or in late 

 Jurassic time. Indeed, it is now the opinion of most geol- 

 ogists that the prime movement (perhaps the intrusion) of 

 the granitic core of the Sierra Nevada occurred at this 

 period and was unquestionably the principal agent of both 

 the folding and metamorphism of the pre-Cretaceous sedi- 

 mentary rocks. Undoubtedly the diversification of the 

 surface was considerable before the inauguration of the 

 Cretaceous period, notwithstanding the subaerial reduction 

 during the long land interval following the Mariposa epoch. 



It is interesting to remember in this connection the two 

 parallel granitic axes of the Pacific border, most noticeable 

 in the central portion of California, between which most of 

 the Cretaceous and later deposits lie. It might be better to 

 refer them only to borders of the Great Valley region of 

 CaHfornia, were it not for the suggestiveness of well known 

 facts outside of this latitude. 



Nearly parallel to the granitic core of the Sierra Nevada, 

 a similar granite massif follows the coast from Santa 



