126 
ON THE GEOLOGY AND NATURAL HISTORY 
remarkable and of a most interesting character. Opinions of a somewhat conflicting na¬ 
ture have been entertained in regard to them, owing to the peculiar character of the 
* 
organic remains, but recent observations have convinced me that they are all of Tertiary 
age, and that they are quite widely distributed throughout the far West. The lithological 
characters of the Judith deposit have already been sufficiently described, and it has yielded 
many important fossils. A thin series of beds is also found near the sources of the Mo¬ 
reau, Grand, and Cannon-ball rivers, and at the mouth of the Big Horn river we have a 
group of beds eight hundred to one thousand feet in thickness, with fossils of the same 
character as those occurring at the mouth of the Judith. The collections obtained by Mr. 
H. Engelmann, in Utah, while acting as geologist of Capt. Simpson’s expedition, and sub¬ 
sequently investigated by Mr. Meek, have also established the existence of an estuary de¬ 
posit of Tertiary age in the country bordering upon Green river,—scarcely less interesting 
than that of the Judith. These deposits pass up into the true lignite beds without any 
perceptible line of separation, gradually losing their estuary character, and ever after con¬ 
taining only land and freshwater shells. The lignite strata are chiefly remarkable for 
yielding in the greatest abundance finely preserved vegetable remains. A few fragments 
of leaves of Dicotyledonous trees and silicified Avood, Avitli very impure lignite beds, are 
formed in some of the estuary deposits, but no groups to indicate the great luxuriance of 
vegetation which must have existed during the accumulation of the lignite strata. 
The geographical extension of the lignite deposits of the West is iioav a matter of the 
highest interest, and from Avhat is already known, I am convinced that they Avill yet be 
found to cover a greater or less area on both sides of the main divide of the Rocky moun¬ 
tains, from the Arctic sea to the Isthmus of Darien. The estuary and lignite beds seem 
also to have partaken, equally Avith the older fossiliferous rocks, of the influence Avhich ele¬ 
vated the mountain chains. Along the Laramie mountains, and from the Red buttes to 
the divide betAveen Platte and Wind rivers, along the Big Horn mountains, the strata in¬ 
cline at very high angles, 40° to 80°, and in some instances are very nearly vertical. The 
true lignite strata seem to conform to the older fossiliferous rocks, and to have been dis¬ 
turbed by the same influences that elevated the mountain ranges in the vicinity. These 
Tertiary beds extend over all the plain country to the north and east of the Laramie moun¬ 
tains, far to the northward, beyond the limits of our explorations. Crossing the Wind 
River mountains, Ave find them largely developed high upon the western slope, dipping at 
a high angle, from the Wind River range on the one side, and the Wasatch and Green 
River mountains on the other. 
Throughout the Wind river valley is a series of beds of great thickness, Avhich seem to 
be intermediate in their character between the true lignite beds and the White river Ter¬ 
tiary deposits. We first observed them gently inclined near WilloAV springs on the North 
Platte, and thence AvestAvard toward the Sweet-water mountains, and near the divide be- 
