464 DILLER AND STAXTOX THE SHA8TA-CHTC0 SERIES. 



The Shasta-Chico series is composed of the Knoxville, Horsetown and 

 Chico beds, all of which are well exposed in the same sections upon the 

 western border of the Sacramento valley. 



The Knoxville, Horsetown and Chico beds are each characterized by 

 its own fauna. The faunas of adjacent beds, however, are so bound 

 together by many common species that there is no paleontologic break 

 anywhere within the series. 



The Shasta-Chico series is conformable throughout and the intergrada- 

 tional character of the sediments, taken in connection with the faunal 

 continuity of the series and its relation to the great unconformity be- 

 neath, shows that it is the result of continuous deposition. 



The attenuation of the Shasta-Chico series westward from the Sacra- 

 mento valley and the overlapping of the newer beds upon the older 

 crystalline rocks of the Coast range shows that the Coast range was 

 formed before the deposition of the Shasta-Chico series, and probabty at 

 the close of the Jurassic when the Mariposa beds were upturned. 



The successive peripheral attenuation of the lower beds and the land- 

 ward overla23ping of the upper ones shows that the Pacific coast from 

 Alaska to Mexico was subsiding and the sea transgressing. 



The subsidence was probably not uniform throughout the whole re- 

 gion. The deposition of 30,000 feet of sediments in the Sacramento 

 valley under shallow-water conditions apparently indicates a greater 

 subsidence in that region than for the mountains from which the sedi- 

 ments were derived. 



The -Mariposa and Knoxville beds are faunally distinct and uncon- 

 formable. The former is Jurassic and the latter Cretaceous. 



The final folding of the Sierra Nevada rocks and an uplifting of the 

 range occurred at the close of the Jurassic. 



The Shasta-Chico series represents the Cretaceous time from the be- 

 ginning of the Lower Cretaceous to the middle of the Upper Cretaceous, 

 and it may be closely correlated with the Queen Charlotte Island and 

 Nanaimo groups. 



The fact that certainly 4 and possibly 14 out of 22 fossil plants found 

 in the Knoxville and Horsetown beds of California are identical witli 

 forms found in the Potomac formation of the Atlantic border indicates 

 that the Potomac epoch is included in that represented by the lower 

 part of the Shasta-Chico series. 



The relation which the Comanche series of Texas and Mexico is be- 

 lieved to hold to the Aucella beds of that region and also to the Upper 

 Cretaceous renders it highly probable that it is contemporaneous with a 

 large part of the Shasta-Chico series. 



United States Geological Survey, 



Washington, D. C, March 20^ 189 If. 



