Page:Popular Science Monthly Volume 15.djvu/327

Rh deluging the lowlands with lava-floods, or discharging into the atmosphere 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 cañons 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 continuously 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 extent. 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 excursions 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 important 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, accumulated, 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 longitude 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 deposits 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