288 EXPLORATIONS ACROSS THE GREAT BASIN OE UTAH. 



thinner portions of the solid crust yielded more, and resumed the lower position which 

 they still occupy. 



This formation, as developed about Fort Bridger, presents the following section in 

 descending order : 



1. Arenaceous and argillaceous shales, slates, and shaly sandstones of green color, 

 with interstratitications and concretions of coarser gray and green sandstone, which, 

 at some points, form regular round bodies like cannon-balls. The lower portion con- 

 tains, also, slaty sandstones and calcareous slates, and thin seams of an oolitic, fetid 

 limestone, forming a transition to the middle portion. The thickness amounts at least 

 to from 200 to 300 feet. 



2. Limestones and argillaceous shales, also arenaceous shales, and areno-calcare- 

 ous slates. The white color prevails. The limestones are partly oolitic, partly sub- 

 crystallino, with eonchoidal or splintery fracture, partly uncrystalline, earthy, or chalky, 

 also siliceous, arenaceous, and argillaceous; and many of them are fetid on account 

 ot the large amount of organic remains which they contain. Over 100 feet. 



:'). Tight colored, mostly white, rather fine-grained sandstones, in thick beds, 

 regularly alternating with mostly light red arenaceous and slightly argillaceous shales, 

 and sott shaly sandstones. Over 200 feet, and perhaps considerably more. These 

 strata may. possibly, be older than Tertiary(?). 



The strata No. 1 are peculiarity apt to form prominent bluffs and table-hills, many 

 of which are known as conspicuous landmarks. Generally one of the harder beds of 

 sandstone tonus the nearly horizontal top, while in the bare, precipitous sides the 

 shales prevail. These shales are frequently covered with efflorescences of salts. On 

 our road they were most characteristically developed along Black's Fork; they also 

 form the bluffs near Green River, and the upper part of the bluffs around Fort Bridger. 

 They gradually change into No. 2, and while the upper portion appears to contain 

 only few organic remains, the beds of transition and No. 2 are loaded with them. On 

 the banks of Green River I observed, in the fetid oolitic limestone, and the green 

 slates ot these beds ot transition, remains of fishes, not distinct enough for identifica- 

 tion ot the species, and obscure impressions of plants; also, crystals of gypsum, and 

 efflorescences ot a salt, which proved to be a mixture of sulphate of magnesia and 

 sulphate ot soda, while other salts of this vicinity are pure sulphate of magnesia. In 

 the same horizon, near the mouth of Harris's Fork, I observed some gray laminated 

 slates, full ot impressions ot plants, mostly ferns, and, close by, brown carbonaceous 

 shales, which might, in their continuation, form beds of lignite.' The slates, becoming 

 siliceous, torm gray, brown, and black compact rocks, with numerous marks of 

 Eqinsrtnni, etc., and contain seams of fibrose gvpsum. 



A tew feet below them, between layers of green shales, there is a bed of white 

 oolitic fetid limestone, nearly altogether composed of fossils, viz: 2 species of 

 Melania, 2 of Lymwa, Z'nio, Phuwrbis, &c, a description of which will be found in Mr, 

 Meek's report. The same limestone occurs in the bluff southwest of Fort Bridger 

 (Moore's bluff), and in our collection we have specimens of it from a point 15 or 20 

 miles southeast of Fort Bridger, at the foot of the Uintah Mountains. Some of the 

 limestones of No. 2, m the quarry near Fort Bridger, contain numerous traces of 

 organic remains, teeth and scales of fishes, &c. 



