456 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



lions of shells of Anomia and Ostrea, together "with a few of Corbula, Cor- 

 dicula, Modiola^ and Goniohasis, all apparently of different species from (but 

 some of them very closely allied to) those found higher in the series. 

 Again, at Eock Springs, perhaps twelve miles farther westward, and 

 not far below the horizon of the last-mentioned localities, we found 

 numerous specimens of Corhula, Ostrea, CorMcula, ModiOla, and Gonioba- 

 sis, all associated in the same bed, the species being again distinct, except- 

 ing probably the CorMcula and Ostrea, from those found at any of the 

 other localities, though the Corhula and Goniohasis are of the same type " 

 as those found at Black Butte. 



At Black Butte Station, in the bed containing most of the shells al- 

 ready mentioned as occurring there, we found, along with numerous 

 specimens of beautiful impressions of leaves of dicotyledonous trees, 

 some large bones of a huge reptilian.* We also ob,served nearly all 

 through this formation impressions of the leaves of the higher types of 

 dicotyledonous trees, in some instances belonging to the same genera 

 as those composing our existing forests of the temperate zone ; also 

 fragments of fan-palm leaves, and the stems of marine plants.t 



From such a group of organic remains, it seems scarcely to admit of 

 doubt that this formation was deposited in a body of water, which, 

 although salt enough to permit the existence of some marine types, was 

 still probably so tempered by the influx of the streams that brought in 

 the land and fresh- water remains, as to be at least unfavorable to the 

 extensive development of marine life. The presence of numerous beds 

 and seams of coal also indicate that there were alternate elevations and 

 depressions of this whole region during the deposition of this formation. 

 That is, if we admit the most generally accepted theory that such de- 

 posits of coal were formed by the growth, on the spot, of vegetation in 

 marshes at, or a little above, the sea-level. Because we find some 

 marine or brackish water types between nearly all tfie coal-beds, thus 

 showing that after the accumulation of the material of each bed of coal, 

 it was again covered by salt, or at least strongly brackish, water. 



It is not necessary, however, to suppose that each elevation was equal 

 to the preceding subsidence, because the accumulation of sedimentary 

 matter during the interval probably largely compensated for the sink- 

 ing, so that the elevations may have been comparatively very slight to 

 bring the bottom again slightly above the sea-level. At any rate, what- 

 ever theory we may adopt in regard to the formation of such coals, it 

 appears exceedingly improbable that the coal beds of this region were 

 formed by the drifting together of the trunks and fragments of trees 

 and other vegetation 5 because, although we sometimes see small frag- 

 ments of this coal showing woody structure, as we do in those of the old 

 Carboniferous period, they are not in any proper sense lignite, so far as 

 structure is concerned, but seem to have been mainly formed by the 

 growth and accumulation of smaller kinds of vegetation, and are as 

 persistent, compact, and homogeneous as any of the old bituminous 

 varieties. 



From near Salt Wells southeastward to Black Butte Station, this 



* On hearing of these discoveries from some friends from the East, to whom I had 

 mentioned the same at Salt Lake City, Professor Cope visited the locality on his return 

 home, some time in August, 1872, and dug out more of the bones of th^reptilian, which 

 he soon after described in a paper sent on to the Philosophical Society, as the type of a 

 new genus of Dinosaurians, under the name Agatliaumas sylvestris, and expressed the 

 opinion that it proves the rock to be Cretaceous. 



t All of the remains of plants collected from this and other formations by the Survey, 

 have been ably reported on by Professor Lesquereux. 



