204: 
THE GEAND CANON DISTRICT. 
though this ratio varies somewhat. From what we have seen of the Grand 
Canon we must conclude that the Marble Canon would be much more 
impressive if its width were five or six times the depth, instead of double. 
Nothing resembling the great cloister buttes and temples is seen in the 
Marble Canon. It is everywhere characterized by extreme simplicity. But 
the enormous expanse of vertical I’ock-face when seen from below is very 
impressive. Generally, in the deeper portions, the Red Wall limestone pre- 
sents those buttresses with vertical flutings and scorings which characterize 
the same beds in the inner gorge at the Toroweap. It all looks very sol- 
emn, very architectural, and very imposing. 
The only tributary which the Marble Canon receives is the Little Col- 
orado. There are some lateral amphitheaters, but they do not set back into 
the platform more than two or three miles from the river, and they cannot 
be properly called side chasms. But the Little Colorado is an important 
tributary. It heads far to the southeastward among the lavas of the Great 
Black Mesa of east-central Arizona. Its length is nearly 300 miles, and 
its watershed proportionately great ; yet it contributes to the Colorado 
only a very small brook of water in the dry season. In flood time, how- 
ever, the volume is large, for not only is the watershed extensive, but it is 
quite lofty on the whole, being from 7,000 to 8,000 feet over a large part 
of it. At such altitudes the rainfall in the wet season is considerable. This 
stream is everywhere independent of the structural slopes. Its lower courses 
are nearly parallel to the principal structure lines. In the vicinity of the 
Little Colorado the greatest structural feature is the Echo Clifi" monocline, 
and this monocline is nearly parallel to the lower courses of the tributary. 
But far to the southeast the main branch of the stream crosses the flexure 
transversely, entering the ascending slope of the monocline. It soon be- 
comes apparent that this tributary had its course laid out long before the 
existence of any of the great structural displacements, and that it is as old 
as the Colorado itself Its origin goes back to the earliest Teidiary time 
when the I’egion first emei’ged from its lacustrine condition. No other sup- 
position seems capable of explaining the situation of the Little Colorado 
and the independence of structural slopes which it betrays everywhere 
along its course. 
