228 
THE GEAND OASTON DISTEIOT. 
the lower deeps of the entire canon. Everywhere the rapid corrasion of 
the deeper gorges is revealed. The epoch at which this latest upheaval 
took place, is no doubt a very recent one in the geological calendar. It 
began most probably near the close of the Pliocene. That it has now 
ceased is almost certain. No trace of present movement can be detected 
in any of the faults, and it is certain that no movement tending to increase 
them has taken place in those portions which have been scrutinized. In 
the Uinkaret some lava flows cross the Hurricane fault, and though they 
must be thousands of years old they are not dislocated. If any vertical 
movement is now in progress it is nowhere betrayed, and is unaccompanied 
by any of those collateral movements of faulting, which are usually asso- 
ciated with upheaval. 
During the last stage of the evolution of the region we have to con- 
sider a very interesting episode. The glacial period here intervenes between 
the arid climate of the Pliocene and that of the present time. As has been 
already remarked, the glacial period here was not icy, but rainy, and very 
probably colder than the present. In some localities it began to excavate 
systems of local drainage channels and to carve out minuter details of 
topography. In truth the amount of this work which was done in that 
period was quite considerable. The most striking instance is to be found 
in the ravines of the Kaibab. The smaller drainage of the Paria Plateau 
is another instance. West of the Kaibab we fail to find such conspicuous 
traces of the glacial period. The explanation of their absence or feeble- 
ness may be the fact that those western plateaus have scarcely any slopes 
upon which such a drainage system could readily find foothold, while the 
slopes of the Kaibab summit and of the Paria platform are very consider- 
able. The glacial period appears to have been of too brief duration to 
achieve any very great results in this district. It may have increased the 
corrasive power of the Colorado and tributaries by furnishing a larger water 
supply and there is decided reason for thinking that some of the canons in 
the terraces were rapidly corraded and deepened at this time. Most of those 
lateral canons in the terraces are slowly filling up with alluvium at the 
present time, but very plainly they were much deeper at no remote epoch 
in the past. The lower talus in some of them is completely buried and 
