L. Lesquereux— Rocky Mountain Lignitic Formation. 447 
fossil flora, with some difference, has the same characters in 
the strata connected with these lignite-beds, at all the stations. 
The group is therefore satisfactorily limited so far, but where 
does it pass to a higher division of the Tertiary or to the Mio- 
cene? I have already remarked that I consider the conglomer- 
ate formation seen at Evanston and other localities as the up- 
per beds of the Eocene. But I have not myself found any 
oa proof of this assertion, and as these conglomerates have 
n referred to different groups according to the strata which 
they appear to cover, the assertion is contestable. The observa- 
tions, however, of Dr. Hayden, who, after years of careful field 
explorations, has become the true interpreter of the geology of 
the Rocky Mountains, will supply this last evidence. In begin- 
ning his description of the Green River Group, and in marking 
its superposition to the Eocene sandstone, he says: 
This interesting valley (Henry’s Fork) is filled with beds which show a perfect 
conformity. The first bed is a yellow-brown, rather fine-grained sandstone, dip- 
ing 75° a little west of north. Then comes a series of yellow and light-gray 
arenaceous or marly clays, with beds of yellow-brown and light-gray sandstones 
jecting somewhat above the surface. Alternating with these layers of sand- 
pebbles of all the older formations. These conglomerate beds are intercalated 
among the sandstone through 300 or 400 feet in thickness, and are probably of 
Upper Eocene age. ov 0 ne which 
have a diminished dip 20° to 30°, and then pass up into the calcareous layers of 
the Middle Tertiary of Green River group. 
The relative position of the conglomerate as underlying the 
Green River Group is thus positively ascertained. Comparing 
this with what has been described and marked in the section of 
Evanston, Cheyenne, Gehrung’s in Colorado, the lignite basin 
of the Arkansas Valley near Cafion City, the Santa Fé marls, 
the Gallisteo group, &c., such remarkable analogy 1s seen 1n the 
composition and geological distribution of these conglomerates 
that the unity and contemporaneity of the formation becomes 
evident. 
e Lower Eocene. In the following table U stands for Upper 
Eocene, L for Lower, M for Mississippi, where the Lignitic beds 
of the same age are at the bottom of the Tertiary ; E' for Euro- 
* F. V. Hayden’s Geological Report, 1870, p. 69. 
