GEOLOGICAL SURVEY OF THE TERRITORIES. 89 



We have had a severe snow-storm, 6 inches on the plains, and 12 

 inches in the mountains. The mountains are now covered with snow. 

 Very respectfully, your obedient servant. 



F. y. HATDEiT, 



United States Geologist 

 Hon. Joseph S. Wilson, 



Commissioner General Land- Office. 



September 1, 1868. 



Pursuing our course westward, across the Laramie Plains, from Fort 

 Sanders, we took the overland stage-road, which continues near the foot 

 of the mountains on the south side of the plains, and usually from 5 to 

 15 miles south of the railroad-route. I give my notes of the different 

 routes in detail, from the fact that my explorations extended over a 

 region almost entirely new, and also because there have existed no defi- 

 nite data which could be used in coloring a geological map. 



As I have before remarked, the Laramie range of mountains forms 

 one of the most complete and beautiful anticlinais seen in the Eocky 

 Mountains. This range extends from a point near the Sweetwater, 

 southeastward, in the form of a curve, until it is lost in the main Eocky 

 Mountain range near Long's Peak. It forms a conspicuous wall, closing 

 in the northeast and east side of the Laramie Plains. 



The nucleus is red syenite for the most part, while from the margins 

 incline, from either side, unchanged rocks belonging to the Carbonifer- 

 ous, Triassic, Jurassic, Cretaceous, and, in some localities, Tertiary. 

 These beds incline at different angles, depending upon the character 

 of the elevating force. 



The plains of Laramie, as this area inclosed by mountains is called, 

 exhibit a broad undulating, almost treeless surface, about 60 miles in 

 length from east to west, and 50 miles from north to south. 



From Fort Sanders, along the stage-route to Little Laramie, the dis- 

 tance is about 18 miles. The surface is uudulating, but all the slopes 

 are moderate in the inclination. The basis rocks are all of the Creta- 

 ceous period. In the banks of the Big Laramie may be seen a small 

 thickness of the black slates of ]So. 2, and here and there are isolated 

 hills with the yellowish chalky layers of No. 3. Some of the higher 

 ridges, which extend down into the plains from the foot of the mount- 

 ains, reveal here and there the rusty yellowish arenaceous marls of 

 Ko. 5. 



From Little Laramie Station to Cooper's Creek it is 15 miles ; over all 

 this distance the Cretaceous rocks prevail, belonging for the most part 

 to the uxjper portion of that period. There are isolated patches of Ter- 

 tiary probably overlapping the Cretaceous beds. About two miles north 

 of the station, on the west bank of Cooper's Creek, an excellent coal 

 mine has .been opened, with a bed niue feet in thickness. The coal is 

 quite pure, compact, but rather light, ft burns very well, and though 

 I do not think the bed will be continuous over a large area, it will yield 

 a vast amount of fuel. 



The evidence of drift action iii the valley is very striking. The valley 

 of Cooper's Creek forms a triangular area about five miles wide at the 

 base of the mountains and extending down the creek to a gorge through 

 which the stream passes, a distance of eight or ten miles. On the south 

 side there is a hill 500 feet high, with the summit covered with a heavy 

 deposit of drift, and the surface literally paved with worn rocks. 



