THE TOOTH OF TIME. 345 



the streams which traverse the " Great American Desert." 

 For the most vivid descriptions of the geology of this for- 

 saken region we are indebted to Dr. Newberry, the geolo- 

 gist of Ives's Colorado Expedition under the general gov- 

 ernment. The surface formations are mostly of later Car- 

 boniferous and Mesozoic age, interrupted at intervals by 

 mountain-like outbursts of volcanic origin. The region is 

 a vast plateau stretching for hundreds of miles in either 

 direction (Fig. 96). The floor of the plateau is a mass of 

 horizontal strata. Far in the hazy horizon may be seen 

 the bold wall, which rises to a more elevated table-land 

 composed of overlying strata. These higher strata were 

 once continuous over the surface of the lower plateau, but 

 have been swept off by denudation. Still farther in the 

 horizon looms up another gigantic terrace, rising to the up- 

 per plateau of the desert. The traveler journeying across 

 this apparently monotonous and desert plain finds himself 

 suddenly standing on the brink of a precipice. It is the 

 wall of a deep gorge. Down into this gloomy chasm he 

 endeavors to cast a look. It is like a vertical rent through 

 the strata to the appalling depth of more than a mile. 

 Far down at the bottom winds the sky-lighted stream 

 which has executed this tremendous piece of engineering, 

 quiet now as a lamb, but in spring-time roaring and de- 

 structive as a lion. This is the Colorado. Its immediate 

 banks are fringed at intervals by a narrow border of grass, 

 and these meagre grass-plots down in the rocky cleft are 

 the occasional abode of the desert Indian. The great Black 

 Canon of the Colorado is a gorge with perpendicular walls 

 of rock three hundred miles long, and from three thousand 

 to six thousand feet high ! The lateral streams have cut 

 similar gorges, and these almost impassable chasms con- 

 stitute formidable difficulties in traversing the country 

 (Fig. 97). The Colorado has cut through the entire series 



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