AMERICAN GEOLOGY SURVEY UNDER KING. 6lS 



as that of the Laramie Plains, and then sees them sharply and sud- 

 denly rise against the foothills of the Archean, it becomes evident that 

 the entire area of the Rocky Mountains has suffered actual lateral 

 compression, and that the diminution of surface amounts to from 6 to 

 lo per cent." When he further considered that the post-Archean 

 sedimentaries were to be regarded as a mere thin covering over the 

 subjacent crust, he added that "'this diminution of area of actual 

 surface means an actual compression of the solid Archean shell of 

 the earth. 11 



Pursuing the same line of thought, King noted that the configuration 

 of America to-day is due to the configuration or topography of the 

 pre-Cambrian continent. Where Archean faults or mountain chains 

 existed, there were the lines of weakness along which later orographic 

 movements made themselves manifest. A comparatively thin coating 

 of sedimentary beds, foi illustration, overlies the generally smooth 

 Archean rocks of the Mississippi Valley, and here no subsequent dis- 

 turbances have taken place. On the other hand, the high Archean 

 Wasatch ridges, which were covered by 10,00Q feet of sediment in 

 post-Archean times, were again and again uplifted during the subse- 

 quent periods of disturbance. 



It was noted above that, at the close of the post-Cretaceous uplifting, 

 the Wasatch highland stood at an elevation of upwards of 40,000 feet. 

 Under such extraordinary conditions rapid and intense erosion was 

 inevitable, and in a comparatively brief period, geologically, the Ver- 

 milion Creek Eocene lake was tilled with sediments derived therefrom 

 to a depth of 5,000 feet. 



Then ensued another period of disturbance, by which the western 

 portion of these Vermilion Creek beds w T as upturned, while the 

 region to the immediate west, from which their sediments had been 

 derived, was as suddenly depressed, allowing the waters of the lake to 

 extend themselves 200 miles westward into Nevada. 



Another series of crustal movements was now inaugurated in the 

 east, whereby the Great Plains land area also underwent a subsidence, 

 which was most pronounced along the foothills of the Rocky Moun- 

 tains and gradually died out to the eastward. This movement marks 

 the dividing line between the Eocene and the Miocene periods. Con- 

 temporaneously with this the entire Great Basin area, including por- 

 tions of Washington, Oregon, Nevada, and California, lying to the 

 east of the Sierras and the present Cascade Range, became depressed, 

 and, receiving the drainage of the surrounding hills and mountains, 

 was converted into two large lakes which, throughout the Miocene 

 period, were depositories of sediment from the adjacent land. Power- 

 ful and profound crustal movements at the close of the Miocene threw 

 the beds into folds, but did not apparently raise them above the sur- 

 face level of the lake. Contemporaneously with this movement the 



