782 THE POPULAR SCIENCE MONTHLY. 



and Utah, where the river has apparently preserved even its minor 

 sinuosities in a canon thousands of feet in depth. The Colorado 

 River system is a magnificent example of the persistence of rivers. 

 Established ages ago, when only the great general contour of the 

 region was outlined, it antedated all the ranges of mountains and the 

 plateaus which now diversify the surface. Nearly all these uplifts are 

 at right angles, or nearly so, to the courses of the main streams ; yet, 

 in all cases save one, the rivers have preserved their courses, by cut- 

 ting: gorges as the mountains rose. Grand River, which is one of the 

 two largest branches of the Colorado, presents us with a fine succes- 

 sion of these cases. Indeed, it may be said that from its head, in Mid- 

 dle Park, to its mouth, the river is almost continually in trouble ; its 

 course is nothing but a succession of gorges and of transverse valleys. 

 In Middle Park it cuts several minor ranges ; at its point of exit from 

 the park it encounters the Park ranges, which it cleaves from summit 

 to base, making a canon two to three thousand feet in depth. Then 

 follow many miles of precipitous canon, of great depth, which the 

 river has carved in a high plateau. Emerging from this it meets a 

 barrier, in what is known as the Hogback range, through which it 

 levels a passage. Then follows for many miles a deep and narrow 

 valley, between the Book Cliffs on the north and the Battlement Mesa 

 on the south, which looks down on the river from a height of fully 

 four thousand feet. Next, the Little Book Cliffs dispute its passage. 

 These face the west, and toward the east, in which direction the river 

 approaches, have a long and gentle slope downward. The river, hold- 

 ing steadily its course, enters the plateau, and rapidly eats its way 

 below the surface. For many miles its caiion is so deep, narrow, and 

 tortuous, that it can with the utmost difficulty be traced. At the face 

 of the cliffs it emerges suddenly to daylight, in the broad, desert valley 

 of the Gunnison. It holds its normal course across this valle}^ meeting 

 the Gunnison on the west side. Then, right against the bluffs which 

 border the Uncompahgre Plateau, it turns sharply at right angles, and 

 flows off northwest, then west, then southwest again, and south, 

 hugging closely the northern end of this great plateau, while on the 

 right stretches away the desert expanse of the Grand River Valley to 

 the base of the Book Cliffs. 



It may be interesting to trace the behavior of a stream under 

 these trying circumstances, when a mountain-range rises to dispute 

 its path. We are not here concerned with those mountains which 

 have arisen suddenly, by catastrophic action, but only with such as 

 have been slowly evolved. In the former case, rivers, like all other 

 natural features, share in the general overturning and destruction. 

 When an elevation commences gradually across the course of a river, 

 its first effect is to lessen the rapidity of the current above the crest 

 of the elevation and to increase it below that point. The erosive 

 power of a stream is proportional, other things being equal, to the 



