GEOLOGICAL SURVEY OF THE TERRITORIES. 93 



iron, giving to all the rocks of this region a more or less rusty-yellow 

 color. 



In the vicinity of the t3oal-beds are found considerable quantities of 

 brown iron-ore. Large masses were found scattered over the top of one 

 of the ridges which had been melted by the ignition of the coal. The 

 mean trend of the upheaved ridges is about northeast and southwest. 



West of the Medicine Bow the aspect of the country is that of utter 

 barrenness and gloom ; scarcely any vegetation growing except sage and 

 greasewood. Now and then a little lake is seen, but from the alkaline 

 character of the water and the absence of any vegetation around their 

 borders tlney only add to the dreariness of the scene. The dearth of 

 animal life is equal to that of the vegetable. IsTow and then tbe small 

 sage-rabbit, Lepus artemesia ; the little rock-squirrel, Tamias quadrimt- 

 tatus ; and the sage-hen, or the cock of the plains, are seen. 



A few miles west of Fort Halleck there is a very conspicuous hill on 

 the south side of the road, the strata of which incline 25°, though some 

 beds near the summit dip 359. This is called Sheep Mountain. The most 

 conspicuous bed in this hill is a yellow-gray sandstone, 300 to 500 feet 

 thick, the age of which I could not determine. 



From Medicine Bow to Pass Creek, a distance of 27 miles, the road 

 passes through a wide valley, between two upheaved ridges, and nearly 

 on a line between the Cretaceous and the Tertiary beds. 



About five miles before reaching Pass Creek the Cretaceous beds show 

 themselves clearly on both sides of the road. The rusty sands and sand- 

 stones of IsTo. 5 are seen on the right side, while dipping from the flank of 

 Sheep Mountain, on the left, are well shown the clays of No. 2, and the 

 lighter chalky slates of No. 3. 



All along Elk Mountain the red beds appear high up on the flanks, 

 visible, but not conspicuous, and they do not, as usual, color the debris 

 at the foot of the hills. There is an unusual accumulation of Cretaceous 

 and Tertiary in this region, at least 5,000 feet in thickness of each. 



Very nearly north of Pass Creek we have an uplift of yellow, rather 

 fine-grained sandstone, which presents a front like a wall, built up with 

 vertical columns of every form left after erosion. 



The sandstone must have been 150 feet thick. It inclines nearly north 

 at an angle of 19^. As we emerge from the hills near Pass Creek, we 

 come into a broad open plain, and the ridges of upheaval seem to extend 

 oif "en ec/ieZow," as it were, gently bending from the west northward, 

 forming one side or rim of the plain. These ridges of upheaval extend off 

 for miles like waves. They are composed of large numbers of alternate 

 hills of loose yellow sand and indurated clay and yellow sandstone, the 

 whole readily yielding to atmospheric influences, and then the hills as well 

 as the valleys are covered with a great depth of tine sand, from which 

 the harder beds of sandstone project in long lines or walls. These ridges 

 vary in distance from 100 to 1,000 yards apart, a valley always interven- 

 ing, a slope on one side and an abrupt front on the other ; that is, they 

 form monoclinals. The broad plain into which we emerge west of Elk 

 Mountain must be one of depression, or a large area not elevated with 

 the surrounding country, for the ridges of elevation which make so 

 marked a feature all around it die out gradually in the plain. On the 

 east side the ends of the ridges fade out in the level plain, but on the 

 north border they lie along nearly parallel. 



As far as the eye can reach this plain is perfectly level ; no cuts or 

 valleys of erosion to show the underlying rocks. There is a thick de- 

 posit of drift over the whole surface. This vast barren sage-plain 



