GEOLOGICAL SURVEY OF FORTIETH PARALLEL. 313 



deluging the lowlands with lava-floods, or discharging into the atmos- 

 phere clouds of ashes which, borne far eastward by the prevailing- 

 winds, were the agents of more widespread and scarcely less complete 

 devastation. In the end the elevation of the Rocky Mountains, and 

 the erosion of the canons of the Columbia, Klamath, Sacramento, and 

 Colorado, converted the greater part of the rich Tertiary plain into 

 the only real deserts that now exist on the continent. 



Through the center of the region where these great changes were 

 wrought, the belt of the fortieth parallel survey stretches contin- 

 uously for 750 miles, and yet does not reach near to its eastern border, 

 while it covers but an insignificant portion of its north and south ex- 

 tent. It is evident, therefore, that but a small portion of the records 

 which form the history of the Tertiary ages in Western America come 

 within the limits of Mr. King's survey, but he has made wide excur- 

 sions both north and south of his special field, and has availed himself 

 of the observations of his co-laborers in Western exploration, so that 

 he has been able to write this history much more fully than had before 

 been attempted. 



The following brief summary is all we can give of the most impor- 

 tant points in the chapter on the Tertiary rocks, perhaps from its facts 

 and suggestions the most interesting of any in Mr. King's report. 

 During the Eocene four great lakes with different boundaries, and 

 forming different series of sediments, occupied the middle portion of 

 the fortieth parallel belt. These are named by Mr. King : 1. Ute 

 Lake, in which the Vermilion Creek beds, 5,000 feet in thickness, ac- 

 cumulated, and which filled the Green River basin to the width of 150 

 miles, reaching to that distance north of the fortieth parallel, and to 

 a yet unmeasured distance southward ; 2. Gosiute Lake, from which 

 were deposited the " Green River Beds " of Hayden (the Elko Group 

 of King), 2,000 feet in thickness, which extended westward to the lon- 

 gitude of 116, and eastward, perhaps, into Middle Park ; 3. Washakie 

 Lake, in which the Bridger Beds, 2,500 feet thick, were deposited ; 

 this occupied the country about Fort Bridger, reaching some 150 

 miles east and west, and to an unknown distance north and south ; 4. 

 Uintah Lake, a limited body of water south of the Uintah Mountains, 

 which received the last Eocene sediments, a thin group of clays and 

 sands containing fossils, differing from those of the Bridger Group. 



In the Miocene age, the area occupied by the Eocene lakes was 

 mostly dry land, but other lakes not less extensive, and perhaps of 

 equal duration, occupied contemporaneously portions of Nevada and 

 Oregon in the west, and a wide district in the great plains on the east. 

 To the western lake Mr. King gives the name of Pah-ute, and its de- 

 posits he calls the Truckee Group. The eastern Miocene lake he calls 

 Sioux Lake, and its basin contains the strata named by Hayden the 

 White River Group. In the Pliocene a wide extent of the Great Basin 

 was occupied by what Mr. King has named the Shoshone Lake, and 



