CORRELATIVE MOVEMENTS TX THE SIERRAS. 279 



On the Pacific border of the western or Nevada continent, both stratigraph- 

 ical and paheontological conditions are much less easily defined. Whitney 

 and King regarded the Jurassic beds of western Nevada, which apparently 

 overlie conformably the Star Peak or Alpine Trias, as of the same age as the 

 auriferous slates which are upturned against the western flanks of the Sierra 

 Nevada, and considered the uplift of the Sierra Nevada as post-Jurassic and 

 contemporaneous with that which folded the Nevada beds. As the Jurassic 

 fauna of the latter corresponds with that of the marine Jura of the interior 

 region, the movement would closely correspond with the Jurassic movement 

 we are now considering. 



Later observations by Mr. G. F. Becker* and Dr. C. A. Whitef differ in 

 some respects from the conclusions drawn by Whitney and King. They 

 consider the auriferous slates (Mariposa beds) to be palreontologically distinct 

 from the Nevada Jurassic and to be more closely allied to the Knoxville 

 beds of the Shasta group. Dr. White is not fully decided as to their age, 

 but is inclined to place them in early Cretaceous (Neocomian) or late Jurassic. 

 The Chico-Tejon beds, which rest unconformably upon the Shasta group, 

 he considers as in part very latest Cretaceous (in this confirming Mr. 

 King's earlier view) and in part early Eocene. While Mr. Becker does not 

 commit himself definitely to a statement of the change in previous orographi- 

 cal views which this would involve, doubtless because he was on the eve of 

 obtaining further and more decisive data from his proposed detailed study of 

 the auriferous slates of California, he evidently foresees the necessity of some 

 such view as the following, if future investigation confirms the conclusions 

 then reached by Dr. White and himself. This is, that an uplift of the Sierra 

 Nevada region occurred at the close of the Nevada Jurassic which perma- 

 nently excluded the ocean from western Nevada and established the shore- 

 line of the Mariposa beds and their contemporaries west of the crest of the 

 Sierra Nevada, and that the movement which upturned these beds and pro- 

 duced the main uplift of the Sierra Nevada occurred in Cretaceous times 

 previous to the deposition of the Chico-Tejon series and hence may prove to 

 have been closely related to the great post- Laramie movement of the Rocky 

 Mountain region. 



It is an interesting coincidence that in Europe, also, there occurred an 

 orographic movement in Jurassic time, in consequence of which, according 

 to the generalizations of Suess| and Neumayr,§the sea retreated entirely from 

 the middle regions of Europe, where toward the close of this period only 

 fresh-water sediments were deposited, and not until Cretaceous time did ma- 

 rine forms again appear. 



*Bull. No. 19 U. S. Geol. Survey, Washington, 1885. 

 t Bull. No. 15 U. S. Geol. Survey, Washington, 1885. 

 X Antlitz der Erde. II Bd., Wien, 1888, p. 350. 

 I Erdgeschichte. II Bd., Leipzig, 1887, p. 387. 



XXXVII— Bull. Geol. Soc. Am., Vol. 1, 1889. 



