SUEVEY OF COLORADO AND NEW MEXICO. 11 



grass which is especially adapted to the raising of sheep, and I am glad 

 to see that some enterprising persons are making the experiment. The 

 healthfulness of the climate, the nutritious character of the short grass, 

 and the dryness of the ground, not unfrequently covered with small 

 pebbles, must act favorably on sheep. 



That portion of Wyoming east of the Laramie range, and south of the 

 line of the Union Pacilic railroad, is entirely covered with the upper 

 beds of the White Eiver tertiary basin. The valley of Lodge Pole, Crow 

 Creek, and Chugwater, show the formations of this basin very distinctly 

 from mouth to source. The Union Pacific railroad ascends the eastern 

 slope of the Laramie range on a sort of bench of this formation, which 

 seems to be unusually developed, and to extend without much interrup- 

 tion up to the very margin of the mountains, sometimes concealing all 

 the rocks of intermediate age and resting on the syenites. 



About twenty miles south of Cheyenne these beds disappear entirely 

 along the eastern flanks of the mountains, and the lignite tertiary beds 

 are exposed to view. 



CHAPTER I. 



FEOM CHEYENNE TO DENVEE. 



I commenced my labors at Cheyenne, Wyoming Territory, and pro- 

 ceeded southward along the eastern flanks of the Rocky Mountains. 

 My preliminary report will be little more than a transcript of my journal 

 from day to day. It will be, therefore, impossible to systematize it as I 

 would wish, or avoid in many cases repetition. There is great uniformity 

 in the geology of the country, and when one has become familiar with the 

 different geological formations over a small area, he can trace them with 

 great rapidity over long distances. This will account, in part, for the 

 large extent of country which 1 have be«n able to examine in a single 

 season. The geological formations immediately underlying Cheyenne 

 are of. tertiary age, probably pliocene or very late miocene. The beds 

 have been slightly disturbed by the upheaval of the mountain range, but 

 their position in relation to the older tertiary beds shows their deposition 

 to have been of late date. They are found deposited in the valleys and 

 sometimes high on the mountain sides, and it is very seldom that they dip 

 at an angle of more than five degrees. These beds can be traced far north- 

 ward to the Black Hills of Dakota, a distance of three hundred and fifty 

 miles, and they are thus shown probably to be the upper beds or most re- 

 cent formation of the White River tertiary. Along the base of the moun- 

 tains the rocks are mostly pudding-stone, or an aggregate of small water- 

 worn pebbles, mostly very small, but sometimes several inches in diame- 

 ter. These pebbles grow smaller and fewer in quantity as we recede 

 from the mountains until they entirely disappear, and fine sand or marl 

 takes their place. Near Cheyenne there is a bed of fresh- water lime- 

 stone which is much used as lime, and seems to answer an excellent pur- 

 pose in mason work and for whitewashing, and I have no doubt that 

 such beds or layers occur in this basin everywhere. Along the line of 

 the Union Pacific railroad, just before reaching Granite Caiaon, a bed 

 of the most excellent limestone crops out, on the margin of the range, of 

 carboniferous age. This is burned into lime of snowy whiteness and is 

 a great favorite with masons. It contains some fossils of well known 

 carboniferous forms, as Atliyris subtilita, Productus pratteniana, and 

 crinoidal fragments. The red sandstones are exposed in a narrow belt 



