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Mesozoic and Cenozoic Geology and Paleontology. 127 
from the disintegration of the granitic rocks of the mountain range. 
They consist of yellow, gray, and pink sands and marls, which dip 
from 5° to 10° from the mountains. West of Green river the charac- 
ter of the beds is similar to those on the east. They are generally 
brick-red in color, and weather into picturesque bad-land forms. 
Along the edge of the basin they are composed of conglomerates which 
contain pebbles of limestone derived from the adjacent mountains. 
The red character of the strata is due to the wearing away of the red 
Mesozoic rocks. The thickness exposed along the western edge north 
of Thompson plateau is from 500 to 800 feet. On the Bear lake plateau 
the thickness is greater, especially toward the west, and on the eastern 
flanks of the Bear River range it is still greater; it increases also to 
the southward until it is several thousand feet in thickness. The line 
separating the Wasatch from the Green River Group is lithological. 
All the variegated beds that lic below the laminated, light-colored 
sandstones, are referred to the Wasatch Group, and all above to the 
Green River Group. 
The area between Green river and the Big Sandy is covered with 
the Green River Group until the northern portion ot the basin is 
reached. North of the New Fork it is present only as cappings of the 
mesas that stand between the streams. Along the east side of the 
Green, from New Fork southward, the Green river shales and sand- 
stones form bluffs several hundred feet in height. On the west side of 
the river above La Barge creek, the group is present only in isolated 
mesas. South of that stream, however, it is the surface formation ris- 
ing from Green river to the westward, and breaking off in bluffs that 
face Meridian ridge. It consists of a series of light colored sandstones 
which are succeeded by calcareous layers and fissile shales. In the 
Ham’s Fork plateau the group forms the surface of a shallow synclinal; 
it is highly fossiliferous, and contains near the top a layer of bitumin- 
ous shale. An excellent fossil locality may be found on Twin creek, at 
the South end of the Ham’s Fork plateau. It was at Station 14, south 
of Horse creek and-west of Green river, where beds of limestone were 
found completely covered with the petrified cases of caddis-flies de- 
scribed by Dr. Scudder, under the name of Indusia calculosa. 
The Bridger Group may Be observed extending northward from 
Ham’s Fork toward Slate creek, breaking off in low bluffs, in which 
the sombre clays and sands of the group are exposed. Between the 
mouth of the Big Sandy and the Green, on the east side of the former, 
there are variegated sands and marls belonging to this group, which 
weather into bad lands. 
