72 
THE GRAND CAS^ON DISTRICT. 
instantly be attacked by considerations arising from the evolution of the 
drainage system. 
It appears, then, that the Grand Cation district has undergone an enor- 
mous amount of upheaval during Tertiary time. The minimum is nearly 
12,000 feet and the maximum is about 18,000 feet The present altitudes 
of the different portions of its surface mark the difference between the 
amount of uplift and the depth of denudation. In these respects the region 
presents quantities above the average of the western half of the United 
States and which are surpassed only by the great mountain platforms. The 
inference of a great denudation might be traced to remoter consequences, 
and so far as I am able to do so I find indications of agreement with such 
facts as we know ; but knowledge becomes imperfect. 
III. The evolution of the drainage system of the region is a subject 
abounding in facts and inferences which group themselves most harmoni- 
ously with those already discussed. The origin of idvers has hitherto 
received too little attention from geologists, apparently because of the 
intrinsic difficulty which the subject offers in most regions. But it seems 
as if much more use could be made of it than has hitherto been done even 
in regions where there is more or less obscurity. There are certain propo- 
sitions regarding them which may read like truisms, yet which become 
extremely useful when followed out to their obvious consequences. The 
self-evident assertion that a river had a beginning implies a great deal. It 
implies that it originated and developed under the limitations of natural 
laws, and these laws we know. We are tempted to laugh at the assertion 
that water does not run up-hill. Yet it would be easy to point out mau}^ 
cases where vexed questions would have been solved if geologists had not 
forgotten it. 
In former writings I have laid stress upon propositions like the follow- 
ing: that the great rivers of a country are as a rule born with the country 
itself; that their courses were determined by the conditions prevailing at 
the time of their origin ; that their positions once established are (with cer- 
tain qualifications) immutable. From these propositions flow consequences 
of great importance. Thus when we find rivers flowing across or through 
mountain chains and plateaus we must infer that they are older than the 
