GEOLOGICAL SURVEY OF THE TERRITORIES. lid 



detail in order that its beauty and regularity may be understood ; and 

 althoguh I regard it, as well as the Black Hills of Dakota, a more perfect 

 illustration of my theory of the elevation of the Rocky Mountain system, 

 yet it is not as conspicuous an example to the casual observer as he lofty 

 ranges west of Denver. 



From Cheyenne to Granite Canon, near the summit of the first range, 

 the grade of ascent is greater than between any other points along the 

 Union Pacific Railroad. The distance is about nineteen miles, and the 

 difference of elevation between the two places is one thousand eight 

 hundred and sixty- seven feet, or a grade of more than ninety feet per 

 mile. The recent tertiary beds lie close up to the flanks of the moun- 

 tains, over a belt of several miles, affording accomparatively easy transi- 

 tion from the newer formations to the granite nucleus. 



For hundreds of miles either north or south of this line it would 

 be difficult or perhaps impossible to build a railroad across the 

 mountains, but here nature seems to have provided an easy inclined 

 plain to the very margin of the mountain summit. The ridges are very 

 nearly concealed, while on either side they can be seen as formidable 

 as anywhere along the eastern base. 



Close up to the sides of the mountains this more recent formation is 

 composed of water- worn boulders and pebbles, varying much in size, 

 but as we recede eastward toward the plain they disappear for the 

 most part. The same is the case with the drift, which shows clearly 

 that the causes which led to the deposition of these beds operated in the 

 vicinity, and the materials are derived from the mountains near by. 



On either side of this inclined plain, north or south, we can see the 

 upturned edges of the different sedimentary rocks in this region. 

 Between Granite Canon and Cache la Poudre, about forty miles along 

 the foot of the mountains, not only is the scenery rugged and grand to 

 the eye, but the complications of geological structure are very interest- 

 ing. There seems here to have been a jog in the miuor ranges which 

 compose the aggregate range, and several of these smaller ones disap- 

 pear in the plains. The belt of upheaved ridges is here ten to fifteen 

 miles' wide, revealing all the sedimentary rocks, from the carboniferous 

 limestones to the most recent tertiary beds. The peculiar brick-red 

 color of the sandstones, which are supposed to be of the triassic age, 

 gives a singular appearance to the scenery. We have here the carbon- 

 iferous limestones resting upon the granites ; then a series of brick-red 

 sandstones inclining at different angles, with beautiful grassy valleys 

 between the ridges, and little streams cutting through nearly at right 

 angles; then a thin group of sand and marls, which maybe Jurassic; 

 then the whole series of cretaceous beds with their characteristic 

 remains ; then the lignite tertiary beds with coal, all conforming to each 

 other, and all inclining from the mountains at different angles. All the 

 beds just alluded to perfectly conform to each other, but the light-colored 

 rocks, which most attract the eye of the traveler at Cheyenne, do not 

 conform, and were of course deposited subsequent to the uplifting of 

 the mountain ranges. We can see, therefore, that the eastern flanks of 

 these mountains formed a shore line for a great fresh-water lake. 



If we make our investigations still north of this line, we shall find, for 

 two hundred miles or more, that these recent beds jut up against the older 

 sedimentary beds, and in many places rest upon the granites. Sometimes 

 the whitish rocks have been removed by erosion, so as to expose the 

 older ones, but near Laramie Peak they entirely conceal all but the 

 granites. In many places these recent beds are found high up on the 

 flanks of the mountains, in a nearly horizontal position, as if many of 

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