220 
THE GEAND CANOE DISTEICT. 
question of origin becomes at once important, for it indicates to us an initial 
configuration of the surface, which must be taken account of and never 
violated in all subsequent discussion. All inferences or speculations con- 
cerning later displacements and many other groups of facts must be kept 
in strict subordination to it. 
The Plateau Country is one in which the conditions have been remark- 
ably favorable to the stability of the larger drainage channels. On the 
other hand, it has been singularly unfavorable to the stability of smaller or 
local drainage channels. The Colorado and its larger tributaries — those 
tributaries which head in the highlands around the border of the province — 
exhibit everywhere incontestible evidence that they are flowing to-day 
just where they flowed in Eocene time. But the smaller tributaries are 
wanting altogether in some large tracts, and where they do exist they 
usually disclose the fact that they are of very recent origin and have been 
determined by sui-face conditions of recent establishment. In the remainder 
of this discussion these facts assume great importance. 
With the final desiccation of the Grand Canon district began the great 
erosion, which has never ceased to operate down to the present time. Con- 
cerning the details of that process we know but little, and we can only 
guess at its general character during the earlier stages. Erosion is here 
associated with a large amount of uplifting, and we may conjecture that as 
the uplifting went on the inequalities produced by erosion became greater 
and greater, the valleys grew deeper, and the intervening mesas stood in 
higher relief. This is merely an application of the general law that the 
higher the country the more deeply is it engraved by erosion and the 
greater are its sculptured reliefs. Much, however, must depend upon 
climate. But the Eocene climate of the West, so far as it is indicated by 
the strata and organic remains of that age, was moist and subtropical, and 
presumably the climate of the Grand Canon district was similar. 
During the latter part of Eocene time the degrading forces no doubt 
made great progress in destroying and removing the Mesozoic deposits, 
which I have shown originally covered the region. We cannot, however, 
in this district find any epoch separating the later Eocene from the Miocene. 
To all intents and purposes they formed here a single age. From the 
