254 Geology and Botany of Northern Pacific Railroad. 



recent times. Between the rugged rock-masses are level spaces 

 dotted over with bunch grass, sage {Artemisia), and Linosyris. 



The geological substructure consists of a series of Tertiary 

 beds of various kinds, sedimentary volcanic ash, washed down 

 from the highlands, and diatomaceous earth, interstratified with 

 sheets of basalt. It is evident that this belt was for a long 

 time, either wholly or in part, occupied by lakes. During 

 long periods of quiet, all forms of life were abundant ; the land 

 supported a varied growth of arborescent and herbaceous plants, 

 which furnished food to a great variety of animals, while the 

 water was inhabited by fishes and mollusks of many kinds. 

 At intervals, however, showers of ashes, mostly emanating from 

 the volcanic vents of the Cascade Mountains, covered the coun- 

 tay, destroyed, over large areas, all forms of animal and vege- 

 table life, and washing into the lakes, formed strata many feet 

 in thickness. At other times, floods of lava poured down into 

 this valley, spreading over the land and the lake-bottoms, to be 

 covered again in time with other sheets of stratified tufas, or by 

 fresh-water f ossiferous beds. 



The Columbia, Snake River, John Day's River, the Des 

 Chutes, and many minor streams, cut deeply into this plain, 

 and expose in their banks sections of the beds described. In 

 the valley of the Des Chutes, cliffs 1,000 feet in height are 

 formed of them ; and about the Dalles, the remains of horizon- 

 tal Tertiary beds are seen 2,000 feet above the present level of 

 the Columbia. These show that the lofty and continuous chain 

 of the Cascades formed a mighty dam, which kept back the 

 drainage of the interior so that it formed a series of great lakes, 

 bounded on the east by the Rocky Mountains, and on the west 

 by the Cascades, and separated into several basins by the Blue 

 Mountains and others of the desert ranges. 



The accumulated water found an outlet to the sea through the 

 lowest gaps in the Cascade Mountains. Of these, the most im- 

 portant was that where the gorge of the Columbia is now situ- 

 ated ; others exist further south and are now traversed by the 

 the Klamath and Pit River (Sacramento). In the Columbia 

 basin, the old lakes are all drained, or filled, and their bottoms 

 are deeply scored by the draining streams. The lake of the Kla- 

 math basin is now represented by the Klamath Lakes, RhettLake, 



