\ 



GEOLOGICAL SUEVEY OF THE TEERITOKIES. 25 



and others. Near the surmnit of the ridges the gorge becomes very deep 

 and narrow, and the granite rocks are well exposed, with the unchanged 

 beds directly in contact. In the valley of a small stream about four miles 

 above, the unchanged beds extend only up to the foot-hills, while their 

 relation to the metamorphic rocks is perfectly clear. Besting directly 

 upon the granite rocks is a bed of reddish sandstone and quartzite, 

 sometimes so coarse as to be called a pudding-stone, which I have no 

 doubt is Lower Silurian, (Potsdam.) No fossils could be found, but the 

 character and position of the rock render it most probable that it is of 

 that age. Above it, without any apparent unconformability, are beds 

 of limestone and sandstone, which I have regarded as carboniferous, ' 

 though a portion may be of older date. Seceding from the foot-hills 

 is a series of low ridges, of Jurassic, cretaceous, and lignite strata, as far 

 as the eye can reach — far across the Platte. The red beds are not clearly 

 shown, but there are remnants of them on the flanks to show they once 

 existed here. The White River beds which jut up against the sides of 

 the ridge are largely made up of reddish, indurated sand, no doubt de- 

 rived from the ground-up materials of the red beds. Among the car- 

 boniferous rocks of this region are beds that could be made useful for 

 economical purposes. The yellow, rather chalky limestone near the 

 summit of the ridge is rather magnesian, and could easily be wrought 

 into fine building materials. It somewhat resembles the magnesian 

 limestone so much in use near Junction City, Kansas, but it is more 

 chalky. It contains a few small cavities filled with quartz crystals, but 

 not to such an extent as to prove an injury. The surface exposed to the 

 atmosphere is covered with beautiful, basin-like depressions, in which 

 the rain-water accumulates, showing that it is acted upon readily by the 

 atmosphere. The mountain ridge which we have been examining runs 

 out in the valtey of Deer Creek, about fifteen miles above the Box Elder, 

 producing a jog. A second ridge comes in about five miles back of 

 this, which fronts the Platte for ten miles, where the Casper Bidge 

 juts in abruptly and ends with the Bed Buttes. This jog occupies an 

 area about five miles wide and ten miles long, and has been so smoothed 

 by denudation that it is very beautiful to the eye, and always has been 

 an attractive place for herdsmen. 



Eleven years ago I passed a portion of the winter in this valley, con- 

 nected as an assistant with an exploring party under the command of 

 Captain W. F. Baynolds, United States Engineers. Our stock, which 

 amounted to nearly two hundred mules and horses, was wintered very 

 nicely in the valley of Deer Creek near this jog, without a particle of 

 hay or grain, with only the grass which they gathered from day to day. 

 The climate was mild and the snow never deep, so that the ground was 

 always exposed to some extent. The present season the hay for winter 

 use at Fort Fetterman is obtained from this valley. The geology of the 

 valley of Deer Creek is very interesting in its details, and I regretted 

 that I could not spend more time at this point. From its junction with 

 the North Platte for five miles of the valley the lignite beds are well 

 developed, revealing the usual sandstones, indurated clays, &c. Near the 

 mouth of Deer Creek a coal-bed was on fire in the winter of 1859-'60, and 

 I was informed that it is still burning. The surface is heated and much of 

 the earth baked a brick-red color for a considerable space. Five miles 

 up the valley the black clays of No. 4, capped with a thin bed of ferru- 

 ginous arenaceous clays, No. 5, is exposed in the bluffs by the creek. 

 Underlying a long bench which extends down from the foot of the 

 upheaved ridges are two quite striking beds of sandstone. The lower 

 one is concretionary entirely; that is, it is filled with spherical masses 



