Mesozoic and Cenozoic Geology and Paleontology. 103 
nearly 150 miles from the present coast line, and to an elevation of 
nearly 400 feet. 
The Miocene occurs in disconnected patches, in river bluffs and in 
ravines over the seaboard region, and extending from the shore and 
the western margins of the’sounds 50 to 75 miles inland. It consists 
of beds of clay, sand and marl, which are locally filled with shells 
from 2 to 8 feet, and ovcasionally 10 to 20 feet. 
Prof. Theo. B. Comstock* said the Green River Group is used to de- 
signate that portion of the fresh-water Tertiary strata which lies di- 
rectly above the coal group, and which is the present surface formation 
over a large portion of the Green river basin, north of Fort Bridger. 
The upper limit is not readily definable at present, the transition be- 
tween the beds of this and the overlying group being rather gradual, 
but the general character of the two formations, both lithologically and 
palzontologically, differs greatly. The Green river beds are mainly 
composed of a series of shales, marls, and harder calcareous strata, 
the latter especially containing quyntities of the remains of fresh- 
water forms of life, with laminated layers, literally filled with the re- 
mains of land plants of the Phenogamous series. The outline of the 
ancient lake-basin, in which these strata were deposited, is not fully 
determined, but there are indications that its eastern boundary was 
outside of the present limits of the Green river basin, and there is no 
room for doubt that the Uinta mountains, and the Wahsatch cbain, 
then, as now, towered above its surface. Northward it is equally clear 
that the Wind River Range formed the shore of the great lake, with 
probably more or less of gently sloping border during a portion of the 
era of Lower Eocene deposition. ,Uhe excessive erosion has exposed 
the beds over the route from Fort Bridger to near South Pass, and 
generally speaking, the rock contains a considerable portion of calcic 
carbonate, with an abundance of ferric oxide produced by decomposi- 
tion and oxidation. Gypsum and calcite of different varieties are 
abundant, frequently occurring as thin, papery seams between the 
rock-layers, at other times forming masses of considerable extent. 
Some of the layers are little more than a pure clay shale, while there 
are a few quite arenaceous beds and some compact limestones. The 
texture of the different beds is quite variable, but, in general, the 
streams which have cut their channels through them are walled by 
nearly vertical cliffs, and the buttes and benches for the most part have 
* Rep. of Reconnaissance of Yellowstone river andN. W. Wyoming. 
