234 DESCEIPTIVE GEOLOGY. 



reous matter. The strike of the ridges along the line of the railroad is about 

 5° to the west of north, but to the northward they curve rapidly to 

 the west, and form a semicircular line of bluffs, which encloses the valley 

 of Salt Wells on the north. Northwest of Point of Rocks is a higher plateau- 

 like region, which has been preserved from erosion by flows of volcanic 

 rock, which will be noticed further on. In the outcrops of sandstone seen 

 a few miles before reaching Salt Wells Station, and in the low hills to the 

 south and east of that point, the beds have an almost horizontal position, 

 with a slight dip to the eastward. They are largely clays, with some thin 

 intercalated beds of sandstones. 



The axis of the anticlinal is probably still to the westward of these 

 bluifs, and we may estimate about 1,000 feet of clayey beds exposed 

 beneath the sandstones which form the bluff-line just to the east and south 

 of Salt Wells Station. Owing to the want of outcrops, the actual point of 

 change of dip in the beds cannot be observed ; but at the entrance of the 

 canon of Bitter Creek, to the west of the valley of Salt Wells, the beds of 

 massive sandstone dip 12° to the westward. In the section exposed from 

 here to Rock Spring Station are numerous beds of coal, whose correspond- 

 ence with the strata on the eastern side of the fold cannot be determined 

 with any definiteness ; but it is probable that the seams here exposed have 

 a lower hoi'izon than any which have been worked at Point of Rocks or at 

 Black Butte. The lowest seam observed is that of the Van Dyke mine, 

 about 2 miles west of the Salt Wells Valley, which has a thickness of 4 feet 

 of excellent coal, and is overlaid by a red iron-stained sandstone containing 

 thin beds of limonite. This seam is considered to be near the base of the 

 Laramie group. 



From this point to Rock Springs Station the croppings of some ten 

 different coal seams were noticed, but many must have escaped observation, 

 since, in an artesian boring made at Rock Springs Station, no less than seven- 

 teen coal seams were crossed in a depth of 700 feet. The principal bed, whicli 

 has been extensively mined by the Wyoming Coal Company about 2 miles 

 east of Rock Springs Station, has a thickness of 9 to 11 feet, and stands at 

 an angle of 15°. The strike of the ridges at this point is about 30° to the 

 east of north. The fossils found in these sandstones are few, and in general 



