LARAIMIB PLAINS 75 



Trees are wanting over the entire area, except along the broad valleys 

 of streams; but the ridges, benches, and plain are well covered with a 

 luxuriant growth of grass, offering fine grazing land. 



Geneeal Geology. — In their geological aspect, the Laramie Plains are 

 essentially a Cretaceous formation. All the beds of the Cretaceous recog- 

 nized in other localities are represented, from the Dakota well up into the 

 Fox Hill sandstones. The Colorado group, however, covers the greater part 

 of the area, lying in a nearly horizontal position. Along the flanks of the 

 ranges, the entire series of conformable strata exposed in the uplifted ridges 

 east of the mountains occurs bordering the plains, resting unconformably 

 upon the Archaean masses at varying angles, but always flattening out 

 toward the valley. Eising above the plain, on the eastern side, occurs 

 the .broad belt of Palaeozoic strata, which forms the western side of the 

 anticlinal fold, already mentioned as passing over the Laramie Hills. 

 From beyond the northern limits of our map, southward for 55 miles, these 

 Palseozoic beds extend with an unbroken continuity of strata nearly to 

 Harney Station, on the line of the railroad, where they are overlapped by 

 Red Beds, which, from here southward, rest directly on the granite. No- 

 where along the belt of the Fortieth Parallel Survey do the Carboniferous 

 limestones present for so long a distance so uniform a ridge, with as little 

 exhibition of marked flexures or folds, as along the west side of the Laramie 

 Hills. The strata everywhere dip with great regularity at gentle angles; 

 the highest observed dip being 12°, with an average inclination from 5° to 

 8°. High up on the hills, next the Archaean rocks, the lower red sandstones 

 occur, forming a low wall with a steep face toward the older formation, and 

 sloping gently westward. The surface is usually so worn down, and the 

 inclination of beds so slight, that the ridge oiFers but few localities for 

 obtaining sections through the entire series. Only in one or two places 

 have the limestones been cut by deep canons, exposing any very great 

 thickness of strata; the canons just back of Laramie City and Fort Sanders 

 probably presenting the best exposures, with abrupt walls several hundred 

 feet in thickness. The Palaeozoic series, on both sides of the Laramie Hills, 

 show very great similarity in lithological habit. At the base occurs the 

 coarse red sandstone, more or less compact, made up of fine quartz-grains 



