THE DISTKIBUTIOH OF THE EOCENE. 
29 
no upper Eocene strata are found there. But as we go northward towards 
the Uiutas we find later and later formations successively appearing until 
upon the flanks of the Uintas the whole Eocene appears in enormous 
volume, exceeding perhaps 5,000 feet. Could these middle and upper 
Eocene masses once have existed upon the southern portion of the High 
Plateaus and been swept away by erosion? There is strong evidence to 
the contrary. 
Within a few miles of our standpoint on the Markagunt are found 
small patches of water-laid strata consisting of volcanic sand overlying the 
Eocene marls, and upon these are piled massive sheets of andesite and 
trachyte. No apparent unconformity separates the stratified tufa from the 
underlying marls, and to all appearances the deposition was continuous. 
The inference is plain that the lacustrine age closed here amid volcanic 
convulsions, and that the epoch of its closure was at the end of the lower 
Eocene. Similar evidences are found as we examine each successive expo- 
sure to the northward, in which the summit of the lacustrine series is 
revealed; but with the following modification. The beds of volcanic sand 
grow thicker and more numerous, indicating a longer continuance of the 
lake the further north we trace it. And when we pass northwardly beyond 
the limits of the volcanic masses of the High Plateaus, we find common 
sedimentary beds beai’ing fresh-water fossils of middle Eocene age. Still 
further northward we find strata of later and later age, successively making 
their appearance until at last, within sight of the Uintas, the whole of the 
local Eocene is present. 
These facts point to the conclusion that when the desiccation of the 
great lake took place, the portion which first emerged was the southwestern, 
or the Grand Canon district. Perhaps when its southern boundary in 
eastern Arizona and westex’n New Mexico is examined in detail we shall be 
led to infer an equal antiquity for the emergence of those regions, and in 
truth, from the little that is known of them, a suspicion is raised that it will 
so prove. In any event, it appears that the desiccation of the southern por- 
tion of the lake is older than that of the northern, and that its shore-line 
gradually receded northward during middle and upper Eocene time, leav- 
ing dry land behind it, and at the close of the Eocene the last remnant of 
