28 
THE GRAND OAJTON DISTRICT. 
wliich are seen in great volume both nortli and south of the Uinta Mount- 
ains, in the basins of the Green River, of Bitter Ci’eek, and of the White 
and Uinta rivers. Their geological relations and associations, too, are 
quite the same, for the same lake bottom received the deposits of the south- 
ern Uinta slopes and those of the Markdgunt. Those of the Green River 
basin north of tlie Uintas appear to have accumulated in a separate lake 
basin communicating with the one which submerged the southern Plateau 
Province. The interval separating the MarkAgunt from the Uinta region 
is two hundred and fifty miles and more, but the lower Eocene is continu- 
ous between them. It occupies a marginal belt, sometimes narrow, but more 
frequently wide, which was once the locus of the northwestern portion and 
shore line of the great lake. The summits of the High Plateaus, wherever 
the volcanic masses are absent, disclose this formation, and its presence is 
decisively inferred beneath the lavas and their debris. A common bond be- 
tween the two regions is also indicated by the physical conditions attend- 
ing the deposition of these strata. The lower Eocene rests upon the under- 
lying formations, conformably in some places, unconformably in others. 
Where conformity prevails, both the upper and lower series were at the 
time of deposition sensibly horizontal. But in many places the Cretaceous, 
prior to the deposition of the Eocene, was greatly disturbed and greatly 
eroded. And in general the base of the Eocene marks an epoch in the 
geological history of the country, in which an old order of events was 
closing and a new order was making its advent. This revolution was the 
transition of the region from the oceanic condition to that of an estuary 
and lake, and subsequently to that of dry land. The lower Eocene beds 
are brackish- water deposits in the basal members, while higher up they 
become fresh- water. The basal members are coarse and even conglomer- 
atic in their texture, while the middle and higher ones are fine and marly. 
Thus is indicated the complete severance of the lake from the access of 
oceanic waters. Both in the Uinta district and throughout the High Pla- 
teaus these events are recorded in the same order and their meaning is the 
same in both. 
The beds now found in the southern extremities of the High Plateaus 
represent less than half of the duration of Eocene time. No middle and 
