142 GEOLOGICAL SUEVEY OF THE TEERITOKIES. 



across the country northeast and southwest. This valley is about six 

 miles wide. Then the lower tertiary beds arise to the surface with a 

 reversed dip and gradually pass up through a series of sandstones, clays, 

 and arenaceous clays to the Green Eiver shales. At Bock Springs the 

 Wyoming Coal Company, under the direction of Mr. Thomas Wardell, 

 an experienced coal miner, has opened a very valuable coal bed, which 

 is now furnishing large supplies of fuel to the railroad. 



Very soon after leaving Bock Springs Station the Green Biver Group 

 is seen on the bluff hills on either side of the road to the entrance of Bitter 

 Creek into Green Biver. In the Green Biver Valley are seen remarkable 

 sections of strata. I have called this group the Green Biver shales, 

 because it is composed of thin layers, varying in thickness from that of 

 a knife-blade to several inches. The rocks all have a grayish-buff 

 color on exposure, sometimes with bands of dark brown. These darker 

 bands are saturated with an oily substance, which causes them to 

 ignite readily. At one time this material was used as a fuel in stoves, 

 and burned well, giving off a good supply of heat; but it was found 

 that the bulk of earthy matter, after the combustible portion was 

 burned out, was as great as the original mass, and rendered it too in- 

 convenient. One of the cuts along the railroad passes through a layer 

 of the cream-colored chalky limestone. There were one or two beds of 

 this petroleum earth. 



During the progress of the excavations the workmen built a fire 

 by the side of one of the walls, and this oily earth ignited and burned 

 for several days, giving light to the workmen by night, and filling 

 the valley with a dense smoke by day. The best display of the Green 

 Biver shales is near the station on the railroad. At the base of the 

 bluffs we have thin layers of arenaceous clay, with laminated sandstone, 

 with mud markings and other indications of shallow water or mud flats ; 

 color ashen brown, 100 feet. Above, lighter-colored layers with alterna- 

 tions of a greenish layer, fine white sand, the whole weathering a light 

 gray. As we pass up we find a large increase of clay, and some lime, 

 with now and then a thin layer of pebbles or small nodules. The layers 

 vary from the thickness of a knife-blade to twelve inches, split easily 

 and regularly. There are also local beds, four to ten feet thick, of porous 

 limestone, which have the appearance of having been deposited from 

 springs during the tertiary period. There are also seams of very fine 

 limestone that are quite black, so thoroughly is the rock saturated with 

 petroleum. The combustible shales vary in thickness, from two to several 

 feet. Near the summit of the hill, under the yellow calcareous sandstone, 

 there are fifty feet of the shales that contain more or less of the oily 

 material. The hills all around are capped with a deep rusty-yellow cal- 

 careous sandstone, which weathers into the peculiar castellated forms 

 which have given so much celebrity to the scenery in this region. The 

 different shades of color in the thin layers give to the vertical walls a 

 distinct banded appearance. 



About two miles west of the station there is an excavation which has 

 been called the Petrified Fish Cut, on account of the thousands of beau- 

 tiful and perfect impressions of fishes which are shown on the surface 

 of the thin slabs, sometimes a dozen or two on an area of a square foot. 

 Impressious of insects and water plants are also found, as well as of a 

 remarkable specimen of a feather of a bird, which Professor Marsh 

 regards as a unique specimen, forming a most interesting addition to 

 the bird remains of North America. " It is the distal portion of a large 

 feather, with the shaft and vane in such excellent preservation that, it 

 may perhaps indicate approximately the nature of the bird to which 



