OEIGIN OF THE PLATEAU LAKE. 
217 
tinuous lake south of the Uinta Mountains. The vertical movements which 
followed the close of Cretaceous time shut it off from access to the sea. If 
we are at liberty to go on as we have done and to draw broad inferences 
from the drainage channels concerning the mode of evolution, we can very 
quickly frame a theory of the distribution of those vertical movements^ 
Thus we know that during Cretaceous time the Plateau area was wide open 
to the ocean towards the southeast, or towards the Gulf of Mexico. For 
the Cretaceous system stretches from the heart of the province clear across 
New Mexico and into Texas, with no other interruptions than some short 
mountain ranges, (themselves largely composed of Cretaceous strata), and 
such gaps as have very plainly been produced by Tertiary erosion. Let 
us assume that at the beginning of the Eocene, or very soon thereafter, the 
western and northwestern part of New Mexico was uplifted slightly more 
than regions either east or west of it ; the axis of elevation trending nearly 
north and south. The effect would have been to make an almost, if not 
completely, closed basin of the Plateau Country. 
With this hypothesis we are able to frame a very simple and intelligi- 
ble account of the manner in which the Plateau Province finally was isolated 
in Eocene time from the ocean. In truth, three-fourths or more of its bound- 
ary had been marked out long before, perhaps as far back as the begin- 
ning of the Trias ; and in the following way. On the northwest lay the 
Mesozoic mainland, now forming the Great Basin area. In some form or 
other the Wasatch was then in existence as a mountain range. So, also, 
the Uinta chain on the north of the province then existed, but probably did 
not project so far eastward as at present, and left a gap in the boundary 
along the course of the Green Rivei’. On the northeastern side of the basin 
some of the great Park ranges of Colorado were standing, though the 
sea may have washed their bases. But to the southeast the area was wide 
open to the Cretaceous ocean. On the southwest and south lay the Arizona 
mainland so often spoken of in this work. Whether this mainland was con- 
tinuous with the Great Basin mainland we do not know as yet, nor is it 
material just here. If, now, the first effort of the elevating force which has 
raised the continent had acted with more effect upon the eastern than upon 
the western side of the basin, the result would have been to make this basin 
