1. B. Comstock—Geology of Western Wyoming. _ 427 
system in general, except that the rocks of Mesozoic age cover 
the older formations to a greater extent than common. 
lying these, with a very slight dip, and jutting against the 
northern slope of the Uintahs, are the immense fresh water Ter- 
tiary deposits, now eroded to an almost incredible extent over 
the whole basin, which has an area of over 20,000 square miles. 
The junction of these beds with the older deposits is much ob- 
secured by an accumulation of drift material, but at several points 
along Henry’s Fork of Green River, rocks underlying conform- 
ably the red sandstones, which I have referred to the Mesozoic, 
are seen.* ‘The surface Tertiary beds of the southern and west- 
ern portion of the basin appear to belong to Hayden’s “ Bridger 
Group,” of Upper Miocene age,t being composed of dull-colored 
clays with beds of sandstones of considerable thickness, usually 
brownish, or dull yellow or gray, and having more or less of a 
concretionary structure. 
Upon our return to Fort Bridger, the train moved northeast 
through South Pass to Camp Stambaugh. Along our route the 
ridger group is exposed at the surface over a considerable ex- 
tent of country northward and eastward from Fort Bridger, as 
far as Little Sandy Creek and beyond, forming the top layers 
of humerous isolated “ buttes,”{ giving them, when the clays 
eo oinate, the so-called grizzly aspect alluded to by Prof. 
tsh.§ It is impossible, without more extended study, to 
define the lower limit of the Bridger group, but it passes gradu- 
. 
y into a series of marls and limestones containing quantities 
Hayden, is called the Green River group. The buttes of this 
pon not crowned by a considerable thickness of the beds 
«Rag ridger group, have not the grizzly appearance of the 
tter beds. The Green River beds are of Lower Miocene age, 
Journal yo) + ¥ 
ogy Vol. i, Murch, 1871, p. 3.) The I ‘eis 
mainly laminated shales, abundantly ripple-marked, but containing no 
+ Goat I was able to detect. ; 
PD. 55, 58, Survey of Wyoming,” ete., by F. V. Hayden, 1870: Washington, 1872, 
aa term “butte” is used indiscriminately in the west to designate all isolated 
the Me inences standing out prominently in the topography of a country, if 
2 ston in stratified rocks. 
tes which are largely composed of indurated clays are scored by num- 
“i nels or gullies, which run down their sides ina branching and 
Which * pmo causing, at a little distance, that peculiar shaggy appearance 
Siven them the name of “ Grizzly Buttes.” 
