32 



bed of coal, just above it, soon follows; then a bed of shells containing oys- 

 ters, more and less numerous at different points, may be traced for some 

 distance before it also disappears. Near the latter point, a bed of Melanians 

 and other fresh-water shells is seen a few feet above them. 



A section, carried for eight miles south of Black Butte station, exhibits 

 the relation of the Bitter Creek series to the superincumbent Tertiaries very 

 instructively. The whole series rise slightly to the southward, and more dis- 

 tinctly to the westward, so as to form an escarpment as the eastern border of 

 an open valley, which extends south from the railroad, just west of the station. 

 The heavy bed of sand-rock is here, as elsewhere, the landmark and strati- 

 graphical base-line. Moving south from the railroad, we keep along the strike 

 of the lower coal-beds. Just above the sand-rock, the softer stratum thickens, 

 and six miles from the station is covered with the debris of immense numbers 

 of Leptesthes crassatelliformis. Passing over the edges of the strata, toward 

 the southeast, I counted eight beds of coal, separated by various short inter- 

 vals, the eighth being the heaviest, and five or six feet thick. Above this one, 

 three thin beds of lignite were crossed in succession, each accompanied with 

 an abundance of leaves of chiefly dicotyledonous plants. Then came the 

 ninth bed of coal, and then, in order, three more beds of lignite, with abun- 

 dant leaves. During this time the ascent became less steep, and a number of 

 short, level tracts were passed before reaching the upper bed of lignite. 

 Beyond this, I passed another short flat, which was marked by a number of 

 worn banks of the light-ash color that distinguishes the material of the bluffs 

 of the Green River Tertiary which overlie the coal-series near Rock Springs. 

 I had not ridden a quarter of a mile before reaching a low line, from which 

 one of my men picked up a jaw of a small mammalian, allied to the Bridger 

 Hyopsodus or to Hyracotherium of the Eocene of France and Switzerland, and 

 a number of Paludina-like shells. I had thus reached the summit of the 

 Bitter Creek formation, which did not appear to be much more than 350 feet 

 above its base at the railroad. In full view, a mile or two to the south, rose 

 the first of the benches which constitute the horizons of the Green River 

 formation. Between this and the first mammal-producing bed, just described, 

 rose three banks, one beyond the other, measuring, altogether, 120 feet ; perhaps 

 the lowest was 10 feet above the first bank, and this one not more elevated 

 above the last lignite and leaf-bed. In all of these I found bones of Green 

 River Vertebra/a exceedingly abundant, but all dislocated and scattered, so as 



