EASTEEN FOOT-HILLS. 27 



In relation to the broad, elevated range of mountains, they appear to 

 to occupy a very insignificant area, seldom rising more than 500 or 600 feet 

 above their base in Colorado, and 1,000 feet in Wyoming; but from the 

 Great Plains, looking westward, they rise so abruptly and with such con- 

 siderable diversity of outline and structure, that the effect is very striking. 

 This narrow region, bordering the Archaean rocks, varies in width from one- 

 half mile to ten miles, depending partly upon the inclination of the beds, 

 and their detailed structure, and in part upon the height reached by Tertiary 

 and Quaternary beds, which conceal over wide areas the upper members 

 of the Mesozoic series. 



From the extreme southernmost limit of the map northward to the 

 Union Pacific Railroad, the continuity of these sedimentary ridges is un- 

 broken. Still farther to the northward, all along the Laramie Hills, the 

 Palaeozoic beds may be traced for the greater part of the distance, but in 

 places they become so depressed* as to lie entirely beneath the Niobrara 

 Tertiary beds, which abut against the Archaean rocks. 



In their broader geological features, they represent a very simple struct- 

 ure, a series of sedimentary beds resting upon the flanks of the upturned 

 metamorphic rocks, and dipping along the entire length of the range almost 

 invariably away from the mountains; the beds as shown in the Laramie 

 Hills being simply the eastern fold of a broad anticlinal axis. In the de- 

 tails of structure, however, they are much more complex, varying in their 

 dip away from the range, being found lying at every angle from nearly 

 horizontal to vertical. In general they may be said to possess, in the 

 region of the Big Thompson and the Cache la Poudre, a gentle dip, and 

 to increase in the angle of inclination to the northward until they reach at 

 the Chugwater the vertical position. To this rule, however, there are 

 many marked exceptions. These beds are everywhere found to rest un- 

 conformably upon the older Archaean ciystalline rocks. Nowhere, how- 

 ever, for over 100 miles along the front of the range between the Laramie 

 River and Saint Train's Creek, was any non-conformity in the entire 

 series of Palaeozoic and Mesozoic beds observed, while in many localities 

 the relations of beds and their exposures along the streams were such as to 

 show a perfect conformity of dip. In the Laramie Hills, the conformity 



