EVOLUTION OF THE KAIBAB PLATEAU. 
189 
merely a slight elevation between the Kanab and House Rock valleys. 
The subsequent events which have made it what it is may be discerned in 
studying the combined effects of erosion and unequal uplifting. 
The great erosion which has removed so vast a body of strata from 
this region is believed to have been chiefly the work of Eocene and Miocene 
time. The general uplifting, which has prevailed throughout the entire 
extent of the West, had its inception in Eocene time. This is indicated by 
the gradual but somewhat rapid transition of the older areas from a marine 
and estuarine condition to the lacustrine, by the progressive shrinkage of 
the great Eocene lakes and the cessation of widely extended deposition of 
strata. The lake basins, becoming dry, were at once attacked by the de- 
grading forces, and as they rose higher the efficiency of the degrading 
forces augmented. Such indications as we now possess as to the climatal 
condition of the region in those periods are somewhat meager, but are still 
sufficient to warrant the belief that the climate was moist and subtropical. 
Here and there in the surrounding regions we find remnants of temporary 
lakes, some of them of great size, which disclose in their strata abundant 
forms of vegetable and animal life, among which are remains of mammalia 
of great size, with numerous species. These fossils and their associations 
all imply a great exuberance of animal and vegetable life which is hardly 
possible without a moist climate — a climate certainly much moister than 
that now prevailing there, though not necessarily extreme in this respect. 
The palms, which constituted some of the most abundant vegetable forms, 
also show that it was much warmer than at present. Thus a region under- 
going progressive elevation with a moist warm climate may be inferred to 
have wasted away rapidly under the action of degrading forces. 
There are as yet no known facts which enable us to mark the periods 
of Tertiaiy time and co-ordinate them with those Avhich have been estab- 
lished in other regions. Yet there are indications which point to the con- 
clusion that after the vast body of Mesozoic beds had been in great part 
swept away, the denuding forces for a time abated their destructive energy, 
and indirectly we may infer that this diminution of the degrading forces 
had its epoch not far from the close of the Miocene. The great denudation 
up to that epoch had been going on vigorously throughout the whole ot 
