GEOLOGICAL SUEVEY OF THE TEKRITOKIES. 77 



the true cretaceous and tertiary beds will be arbitrary. There are 

 many localites in the West where the line of demarkation is so well 

 defined by the absence of some beds that it cannot be mistaken, but I 

 will discuss this question more fully hereafter. 



Through the broad valley winds the North Platte Eiver with re- 

 markably picturesque beauty, with grassy bottoms, and here and there 

 a group of large bitter cottonwoods. To the south and southeast is a 

 snow-covered range of mountains, walling in the North Park, and form- 

 ing a portion of the water-shed of the continent. Far up the Platte 

 Valley, for thirty or forty miles, the surface is slightly broken, with the 

 appearance that the soft cretaceous clays would give it. 



There is a broad belt of the cretaceous beds extending along the base 

 of the mountains and running across the course of the Platte. To the 

 eastward rise the four rounded mountains of the Medicine Bow range, 

 of which Elk Mountain forms a part. To the north and west the ridges 

 of transition sandstone pass into the true tertiary toward Fort Steele on 

 the Union Pacific Eailroad. 



The bottoms of the North Platte are quite fertile, and produce excel- 

 lent grass. The timber is not abundant, but taken in the aggregate 

 there is enough to supply the sparse population that will be likely to 

 settle in this region. The mountains would furnish a most abundant 

 supply. 



The sandstoues as seen along the Platte are somewhat variable in 

 color and texture. The three lowest and most massive beds, fifty to 

 eighty feet in thickness, are drab brown ; the fourth one is yellowish 

 gray, very friable, separated into thin layers, and weathered into some- 

 what fantastic forms, one of which resembles a human face. This bed 

 of sandstone is full of large, rusty-brown, concretionary masses, which 

 are also divided into thin layers, but are calcareous, really arenaceous 

 limestones. In looking at the surface features of this portion of the 

 country, these four beds of sandstone mentioned above stand out in 

 relief, and give force to the scenery. Between them are some thin 

 layers of sandstone and arenaceous limestone, with seams of dark-brown 

 siliceous clay, more or less slaty. The dip of these beds is persistently 

 northeast. 



Leaving the North Platte we traveled in a northeast direction over 

 uplifted ridges for a time. Soon they are so worn down that they are 

 only faintly shown above the surface, and for about twelve miles before 

 reaching Pass Creek our road was over a level plain covered with a 

 thick deposit of drift. The evidences of erosion are very conspicuous 

 between the North Platte and Pass Creek. The broad, level plain was 

 once covered with ridges of cretaceous beds inclining at a large angle. 

 On the east side of the plain the ridges dip west and northwest from 

 the mountains. On the southwest side of Elk Mountain are very high 

 ridges of sedimentary rocks, but they are only a few miles in extent. 

 The main ridge, which lies next to the granite, is composed of carbonifer- 

 ous limestone. The valley near it, is formed by the scooping out of the 

 soft, red, arenaceous clays of the triassic ; then comes Jurassic, cretace- 

 ous, and lastly the tertiary beds, gently inclining toward the plains. 



These formations are more or less conspicuously shown, depending 

 upon the texture of the materials. The granite mountains rise up about 

 two thousand feet above the base; the ridge of carboniferous limestone 

 is five hundred to eight hundred feet; the third ridge is cretaceous, one 

 hundred to one hundred and fifty feet, while the drab sandstones of the 

 transition group pass off northward in a series of low ridges. 



Leaving Pass Creek, we enter Eattle Snake Pass, with the drab sand- 



