HISTORY OP DEFORMATION IN GREAT RASIN PROVINCE 243 



which created it was probably in late Cambrian or post- Cambrian times, 

 although it may have been later. That it was differential and was 

 locally accompanied by folding and faulting is probable, but certainly 

 the disturbance was not extensive, since within this ancient continental 

 area the Carboniferous and Cambrian rocks seem nearly everywhere con- 

 formable. 



POS T-DE VON I A N MO YEMEN T 



Somewhere near the close of the Devonian or the beginning of the 

 Carboniferous there was a general depression of the Silurian-Devonian 

 continent below the level of the ocean, as is shown by the fact that there 

 were deposited on it the same thick Carboniferous sediments as in the 

 region farther west. This depression may have been accompanied by 

 folding in some places, but so far there is no evidence of it, and from the 

 general conformability of the Cambrian and Carboniferous, where these 

 occur nearly or actually in juxtaposition, it is probable there was no 

 widespread deformation. 



POS T- CA RB ONIFER US MO YEMEN T 



Mr King has reasoned* that after the Carboniferous period the region 

 between the Wasatch and longitude 117 degrees 30 minutes in Nevada 

 was elevated to a land-mass, so that it did not receive any Mesozoic sedi- 

 ments. What were the effects of this movement in mountain-building 

 is uncertain, since they have been obscured to such an extent by the 

 post- Jurassic upheaval. 



POST- J UBA SSIC MO YE ME NT 



The Sierra Nevada, as proved by Whitne}^ experienced its chief fold- 

 ing and upheaval at the close of the Jurassic.f The range consists of a 

 great series of slates and schists, which as a rule dip easterly. The 

 apparent monocline which this dip indicates has been explained J as a 

 series of closely appressed and overthrown folds, the tops of which have 

 been truncated. In this connection it is interesting to note that in the 

 White Mountain range, which lies next east of the Sierras, Mr Walcott § 

 has described an overthrown fold whose strata, however, dip westerly. 



In the western part of the Great Basin the Jurassic and Triassic rocks 

 are highly folded, suggesting that they took part in the post-Jurassic 



* Geological Explorations of the Fortieth Parallel, vol. i, p. 759. 



t H. W. Turner : Rocks of the Sierra Nevada, Fourteenth Ann. Rept. U. S. Geol. Survey, part ii, 

 p. 441. 

 I Le Conte : Am. Jour. Sci., 3d ser., vol. xxi, p. 101. 

 J. S. Diiler : Fourteenth Ann. Rept. U. S. Geol. Survey, part ii, p. 444. 

 § Am. Jour. Sci., vol. xl, p. 169. 



