g2 GRAND CANON DISTRICT. 



audits tributaries have been a system, and not a mere aggregate; for l be 

 latter are dependent upon and responsive to the physical conditions of 



the former. And now we come to the point. The Colorado and its tribu- 

 taries run to-day just where they ran after the region emerged from the 

 waters. Since that time mountains and plateaus have risen across their 

 tracks,' whose present summits mark less than half their total amounts 

 of uplift. The rivers have cleft them to their foundations. 



The Green River, passing the Pacific Railway, enters the Uinta plat- 

 form by the Flaming Gorge, and after reaching the heart of the chain 

 turns eastward parallel to its axis for 30 miles, and then southward, 

 cutting its way out by the splendid caiion of Lodore. Then following 

 the base of the range for a few miles a strange caprice seizes it. Not 

 satisfied with the terrible gash it has inflicted upon this noble chain, it 

 darts at it viciously once more, and entering it, cuts a horseshoe canon 

 in its flank :>,700 feet deep, and emerges near the point of entrance; 

 thenceforward, through a tortuous course of 300 'miles, it flows south- 

 ward through gently inclined terraces, which rise slowly as the river 

 descends. Along this stretch it runs almost constantly against the 

 dip of the beds, cutting through one after another, beginning with the 

 Upper Eocene until its channel is sunk deep in the Carboniferous. 

 Further down, the Kaibab Plateau rose up to contest its passage, and a 

 chasm 5,000 to 0,000 feet deep is the result. It is needless to multiply 

 instances; the whole province is a vast category of instances of river 

 channels catting through plateaus, mesas, and terraces where the 

 strata-dip up stream. The courses of the canons are everywhere laid 

 independently of the topographical inequalities, whether these inequal- 

 ities be due to the broader features of land sculpture or to displacement 

 and unequal uplifting. On the north and west side of the Colorado the 

 tributaries generally run counter to the structural slopes; on the east 

 and south sides, they ran more nearly with them. 



It is clear then that the structural deformations of the surface, the 

 uplifts and downthrows had nothing to do with determining the present 

 distribution of the plateau drainage. The rivers are where they are, in 

 spite of them. As irregularities rose up, the streams turned neither to 

 the right nor to the left, but cut their way through in the same old 

 places. The process may be illustrated by a feeble analogy with the 

 saw-mill. The river is the saw and the rising strata are the timber which 

 is fed against it. The saw-log moves while the saw vibrates in its place. 

 The river holds its place as rigidly, and the rising strata are dissevered 

 by its ceaseless wear. What, then, did determine the situations of 

 the present drainage channels? The answer is that they were deter- 

 mined by the configuration of the surface existing at, or very soon after, 

 the epoch of emergence. Then, surely, the water-courses ran in con- 

 formity with the burface of the uppermost (Tertiary) stratum. Soon 

 afterwards that surface began to be deformed by unequal displace- 

 ment, but the rivers had fastened themselves to their places and have 

 ever since refused to be diverted. 



