GEOLOGICAL SURVEY OF THE TERRITORIES. 71 



Ten miles east of Green River Station, the Green Eiver group disappears 

 abruptly on the south side of Bitter Creek, and the coal formations come 

 up to view. On the north side, the eastern limit of the Green Eiver 

 beds is most sharply marked by a long, high, white bluff, that extends 

 off, far to the northeast, toward the South Pass. 



The dip varies from 3° to 5°, and the laminated calcareous shales 

 gradually pass down into yellow, gray, ami brown indurated arenaceous 

 clays, sands, and sandstones, until the well-defined coal strata are ex- 

 posed, without the least appearance of discordancy. 



Both the middle and the lower tertiary beds incline to the northwest. 

 At Bock Springs the extensive and valuable mines of the Wyoming 

 Coal Company are located. The lignite coal beds continue for a dis- 

 tance of about six miles east of Rock Springs, with a dip of 10°, where 

 a series of yellow and drab-brown indurated clays rise up from beneath 

 the sandstones, and continue for eight miles, to a point about two miles 

 east of Salt Wells Station. This interval forms a sort of low, valley- 

 like space, which is well marked, on account of the rounded and far less 

 rugged style of weathering which extends off to the northeast of the 

 railroad, on one side, and southwest on the opposite side. East of Salt 

 Wells the coal-bearing beds appear again, with an opposite incli- 

 nation, about 10° to the southwest, proving this interval to be a true 

 anticlinal valley. ISTot a fossil was discovered in these clays to fix their 

 age with certainty, but I have no doubt that they belong to the upper 

 cretaceous period, and are an extension, to the north or northeast, of 

 those cretaceous clays already noticed as occurring near the mouth of 

 Henry's Fork, on Green Eiver. I believe it to be the extension north- 

 eastward of the axis of elevation of the Uinta Mountains. I think, how- 

 ever, that it dies out, or is concealed by more modern tertiary beds, be- 

 fore reaching the Sweetwater Valley. 



Continuing eastward from Salt Wells Station, the gradual inclination 

 of the strata exposes a splendid section of the eocene coal beds. 2STot 

 less than 1,000 to 1,500 feet of sandstones and clays are passed over 

 before we come to the valuable coal beds near Black Buttes. At this 

 point the old stage road diverges to the south of the railroad, follow- 

 ing up the south branch of Bitter Creek. 



Soon after leaving Black Buttes we cross the western rim of the series 

 of middle tertiary beds, which 1 have named the " Washakie group." 

 The transition from the coal beds is through a series of indurated are- 

 naceous clays, with beds of sandstones of all colors and texture, bearing 

 upon their surface the evidence of their more modern date. The in- 

 clination is in the same direction and in accordance with the lower 

 tertiaries, but the dip is not more than 3° to 5°. 



At Big Pond Station, fourteen miles east of Black Buttes, the deserted 

 buildings of the old stage station are entirely built of rocks composed 

 of fresh- water shells. There are two kinds of rock, viz, a calcareous- 

 sandstone, formed of an aggregate of Unios, Viviparas, Goniobasis, &c., 

 but all casts, the sandstone being so porous that the calcareous shell 

 has been entirely dissolved away ; still the rock itself effervesces very 

 briskly on the application of hydrochloric acid. Another bed, varying 

 in thickness from six to twelve inches, is a very compact limestone, 

 somewhat siliceous. This is simply an aggregate of Goniobasis cemented 

 with a little lime and silica. The texture of the rock is so close that 

 it is difficult to obtain any perfect shells. 



Table Eock is a high, flat-topped u butte" north of this point. The 

 underlying yielding clays are protected from erosion by these beds of 

 shell rock. All the rocks used for building purposes along the railroad 



