34 
ON THE GEOLOGY AND NATURAL HISTORY 
vicinity of the mountain chains, until we reach a point near the mouth of Little Rocky 
Mountain creek, not far above longitude 108°. We then find that the more recent fossili- 
ferous rocks are thrown up and tilted at every angle, and not far distant on either hand 
we can see the more immediate causes of this disturbance. On our left, about fifteen 
miles from the Missouri, the Square buttes rise up out of the midst of the prairie like 
gigantic castles, composed of basaltic and other trappean rocks. These buttes are from 
500 to 700 feet in height and cover an area of about three miles in circumference, appa¬ 
rently isolated from the other upheavals in the vicinity. About sixty miles to the west 
may be seen the Judith mountains, a much larger and loftier range, which seem to be of 
a geological structure similar to that of the Black hills and Laramie mountains. Far in 
the dim distance, just on the verge of the horizon, and white as if covered with perpetual 
snow, are the Girdle and Snowy mountains, quite formidable outliers of the great Rocky 
Mountain range. On our right, about thirty miles from the Missouri river, we observe 
the Bear’s Paw and Little Rocky mountains, small isolated ranges, from thirty to fifty 
miles in circumference, the highest peaks of which are from 1500 to 2000 feet above the 
surrounding prairie. All these isolated upheavals or outliers seem to represent the dying 
out of that intense subterranean power which elevated the vast central chain. 
If we return and ascend the Shyenne river, the first indication of upheaval which comes 
to our notice is Bear’s peak, near longitude 1031°, rising cone-like to the height of 1500 
feet above the surrounding country. This peak is also composed of trachytic and basaltic 
rocks, and seems to have exposed around its base the fossiliferous beds no lower down 
than the Jurassic or the upper portion of the Permian. We can thus form some idea of 
the vast area in the northwest, occupied by rocks with strata holding a nearly horizontal 
position. 
If we pass up the valley of the Platte river from its mouth, near lat. 41°, long.’96°, we 
find the strata undisturbed until we reach Fort Laramie in lat. 421°, long. 104?°. About 
five miles north of the Fort we see the eastern end of a series of ridges formed of numerous 
conical peaks from 100 to 700 feet in height, the central nucleus composed of a coarse 
flesh-colored feldspathic granite, surrounded by a series of beds of stratified azoic rocks 
tilted at all angles. The lowest ridges or more gentle upheavals are usually capped with 
beds of Carboniferous limestone, which incline at various angles from 5° to 30°. The 
Tertiary formations in this region belong to the later Miocene period, and, as far as I could 
ascertain, have not been disturbed in this immediate portion of the country. West of 
Fort Laramie, on the south side of the Platte, sixty miles distant, we can see Laramie 
peak, the highest elevation in this region. 
This immense mass of rock, which is about 7000 feet in height above the surrounding 
country, is composed principally of granite, while around its base and sides, as if thrown 
