196 
THE GEAND CANON DISTRICT. 
plateau had received its present structure, and that they were determined 
by it ? 
But the great park valley is in complete contrast to all this. Throughout 
its northern portions its course is in direct opposition to the structural slopes 
and throughout its southern jjortion it lies obliquely across them. Every- 
where it is independent of them. What better evidence conld there be that 
it was laid out before the plateau had received its present structure and that 
it was not determined by it ? Its greater antiquity than that of the other 
valleys is attested by many evidences. Its aspect is strikingly different. 
It is very wide while the others are very narrow. The widening of valleys 
is a familiar phenomenon in this region. Those canons which are now dry 
are everywhere widening without becoming deeper. 
The other ravines are not apparently very old. My conjecture is that 
they had their origin in the glacial period. In this region that period was 
not properly glacial, but rainy. Not a trace of glacial action is discovera- 
ble upon the Kaibab. But the evidence of a much moister climate than 
the present one in southern Utah and Arizona is conclusive. The exist- 
ence of such lakes as Bonneville and Lahontan during the glacial period 
admits of no other interpretation. The ravines of the Kaibab were un- 
questionably scoured out by running water. At the present time such 
action has entirely ceased, and it is probable that the ravines are very 
slowly filling up with soil and sand, and it is certain that they are not deep- 
ening.* I can frame no conjecture so satisfactory as that which supposes 
that during the glacial period the rainfall was sufficient to sustain living 
streams in these ravines and that they were then carved by running water. 
Prior to the glacial period the climate was arid like the present. In a coun- 
try like this, where the strata are liorizontal or dip but slightly, the effect 
of an arid climate ujjon the drainage is to obliterate the greater part of the 
channels and to increase the area of the individual drainage basins. A few 
' lu Chapter VII I have adverted to the fact, that although the rainfall of the Kaibab is very 
considerabie — perhaps 25 or 30 inches per annum — there is not a living stream upon its surface. In au 
ordinary region such a precipitation would sustain many creeks and brooks. But here the water sinks 
at tnce into the earth and reappears in the ]trofouuder depths of the great amphitheaters and gorges 
which open into the Grand Canon. The case is a very striking and suggestive one and seems to be 
analogous to the limestone country of Kentucky. The existence of subterranean streams beneath the 
Kaibab is apparently well attested. They emerge usually from galleries situated at the base of the Red 
Wall group and sometimes still lower. 
