74 
THE GRAND CAlJON DISTRICT. 
To apply this reconstruction to every drainage channel in detail 
would lead to an interminable discussion of the dryest and most repulsive 
kind. An example must suffice. Take the Marble Canon in its relations 
to the Glen Canon above it. The Colorado in the Glen Cation flows 
tln-ough 150 miles of Mesozoic strata, the walls being for the last 50 miles 
chiefly in the Cretaceous and Jura. At the foot of this chasm the river 
emerges through a gateway 2,400 deep upon the Marble Canon (Carbon- 
iferous) platform. Just as it approaches the end the Echo Clitf monocline 
tui’ns up the entire stratigraphic system to the westward, with a displace- 
ment, the amount of which is not accurately known, but which exceeds 
certainly 3,000 feet. The age of this flexure is Tertiaiy, for it involves 
the Cretaceous beds and farther north involves the Tertiary. That the river 
at this point has cut through the entire Mesozoic and Permian, and proba- 
bly also the Eocene, is self-evident. Imagine now at a given epoch in the 
early Eocene the river situated only a few hundred feet above sea-level, 
and all these beds lying beneath its trough. Imagine the monocline 
smoothed out. This gives us the position of the Marble Canon platform 
at the stated epoch; viz, 7,500 to 8,000 feet below sea-level. To maintain 
the river we must restore that thickness of later strata. 
Let us suppose now that these strata thinned rapidly along the course 
of the Marble Canon. The supposition speedily raises difficulties. That 
would imply that the Carboniferous platform had a long upward tilt in that 
direction at a considerable angle, and that this tilt has since come back to 
approximate horizontality. Now in truth there is a tilt of this kind, but it 
amounts to less than one degree, and we may assume that it is con- 
genital so far as the river is concerned. If true it would not materially 
affect the conclusion. But the arbitrary assumption of a much greater tilt 
and its subsequent reduction without a trace of evidence is hardly an 
admissible argument. A still greater difficulty is encountered by applying 
the test to the Little Colorado, which joins the main river at the foot of the 
Marble Canon. This tributary has had the same kind of battles to fight in 
order to maintain its right of way as the Colorado itself In no stream 
could the fact be clearer that it has cut through thousands of feet of strata, 
and we know pretty nearly how much. It flows northward to its junction 
