THE RIVER GORGE. 53 



There stand great cities on its alluvial banks. The crumbling 

 bluffs by spells slide into the river. Above the limits of city 

 populations the river is already gathering' in the mud destined 

 to journey to the Gulf of Mexico mud which has already 

 been floated from some remoter region and deposited here at 

 times of overflow. Here comes the Niobrara, with slime from 

 the prairies of Nebraska; the Cheyenne, with washings from 

 the mining camps in the Black Hills ; the Little Missouri 

 and Yellowstone, with sands worn from the Big Horn, the 

 Wind River, and the Snow Mountains ; here, on a grassy 

 plain, unite the Jefferson, Madison and Gallatin tributaries, 

 which bring the dust of the continent from the high water- 

 shed of the Red Rock Mountains, which parts the continental 

 drainage to opposite points of the compass. It is a bewildering 

 breadth and complexity of operations. Over every foot of this 

 wasting expanse the land is yielding to the corrosive action of 

 rivers and rains and frosts. The proud mountain domes and 

 pinnacles are coming down to acknowledge the supremacy of 

 the powers of denudation. The Rocky Mountains have begun 

 their journey to the Gulf of Mexico. Cubic miles of their 

 granitic substance are buried in the delta of Louisiana and the 

 bar of the Mississippi. 



Now that we discover in action the forces which could 

 transform the face of the land in some hundreds of thousands 

 of years, we take a new view of the aspects of the terrestrial 

 surface which had already been acquired when man came into 

 existence. We discover that the face of the earth had already 

 been transformed before we began our observations on it, and 

 by means of agencies which corroded the rocks and carried 

 away the materials precisely as the forces of nature are wast- 

 ing the continent before our eyes. We have already recog- 

 nized the fact that aqueous erosion cut through the Straits of 

 Mackinac and chiseled down the steep sides of the monumental 

 island in the Straits. We have seen the deep precipitous- 

 walled gorge of the Niagara, and the rock-bluffs bounding on 

 certain sides the basins of the great lakes the works of 

 rivers and waves. 



