164 GEOLOGY. 



the thickness of the crust involved in the deformation would be about 

 three and a half miles. 



Within the United States, comparable, if less extensive, elevations, 

 deformations, and faultings took place along the southward continu- 

 ation of the Laramide range. At every point where the Rockies 

 have been studied, the post- Laramie deformation has been found to 

 overshadow both earlier and later deformations. Dana has called the 

 whole chain of mountains which received its initiation at this time, the 

 Laramide system. 1 



West of the Rockies, there were also orogenic movements along 

 more or less parallel tracts. Many of the ranges of the west have 

 not been studied in detail, but most of those whose history has been 

 worked out show deformation at this time. Here may be mentioned 

 many of the mountains of Colorado 2 and Wyoming, and the Wasatch 

 and Uinta Mountains of Utah. In northern California and southern 

 Oregon there were deformations, as shown by the unconformity between 

 the Upper Cretaceous and the Eocene, but the deformation here seems 

 to have been less intensive than farther east. Locally, however, it is 

 thought to have been sufficiently violent to develop the anomalous sand- 

 stone dikes of northern California (Fig. 417, Vol. I) 3 . In British Columbia 

 west of the Gold range, there had been a broad tract of deposition 

 250 miles in width. The beds (largely igneous) which had accumu- 

 lated in this syncline, estimated, in the usual way, to be 40,000 feet 

 (maximum) in thickness, suffered deformation at this time. Meta- 

 morphism here was so intense as to make the separation of Archean 

 and later rocks impracticable. 4 As in the Laramide range, the relief 

 produced was great. In intensity of tangential thrust, the disturb- 

 ances of this time were in contrast with those of other periods through- 

 out most of the area between the Sierras on the west and the Great 

 plains on the east. 



Faulting. — The mountain formation at the close of the Cretaceous 

 period was accompanied by faulting on a somewhat extensive scale 

 throughout the region of movement, though the faulting of this 



1 Dana, Manual of Geology, 4th ed. 



2 See folios of the U. S. Geol. Surv. for Colorado, Wyoming, and Montana. Also 

 Emmons, Bull. Geol. Soc. of Am., Vol. I. 



3 Diller, Bull. Geol. Soc. Am., Vol. I, p. 411; and Downieville, Cal., folio, U. S. Geol 

 Surv. 



4 Dawson, loc. cit. 



