Mesozoic and Cmnozoio Geology and Palmontology. 269 



from the disintegration of the granitic rocks of the mountain range. 

 They consist of j^ellow, 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 lie 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 ot Indus ia calcvlosa. 



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 Sand}- 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. 



