SUEVEY OF COLORADO AND NEW MEXICO. 95 



aboimd caunot l)e less than fifty square miles. Indications of large deposits of iron ore 

 have been found in inauy other localities along the line of the Pacific railroads, and if 

 the mineral fuel which is found here in such great abundance can be made useful for 

 smelting purposes, these lignite and iron ore beds will exert the same kind of influence 

 over the progress of the great West that Pennsylvania exerts over all the contiguous 

 States. When Ave reflect that we have from ten thousand to twenty thousand square 

 miles of mineral fuel in the center of a region where for a radius of six hundred to one 

 thousand miles in every direction there is little or no fuel either on or beneath the sur- 

 face, the future value of these deposits cannot be overestimated. 



The geological age of these western lignite deposits is undoubtedly tertiary. Those 

 on the Upper Missouri have been shown to be of that age both from vegetable and 

 animal remains, and in the Laramie Plains I collected two species of plants, a Populus 

 and a P?a«?fl?i»s, specifically identical with those found ou the Upper Missouri. The 

 simple fact that cretaceoiis formations Nos. 1, 2, 3, 4, and 5, are well shown all along the 

 toot of the mountains, and that No. 5 presents its usual lithological character with its 

 peculiar fossils, within fifteen miles of Marshall's mines, also that at the mine, 2, 3, and 

 4 are seen inclining at nearly the same angle and holding a lower position than the 

 lignite beds, is sufficient evidence that the strata inclosing the lignite beds are newer 

 than cretaceous. A few obscure dicotyledonous leaves were found, which belong rather 

 to tertiary forms than cretaceous. 



The connection of the lignite deposits on the Ujiper Missouri has been traced unin- 

 terruptedly to the North Platte, about eighty miles above Fort Laramie. 



They then pass beneath the White River tertiary beds, but reapjiear again about 

 twenty miles south of Pole Creek, and continue far southAvard into New Mexico. 

 Near Red Buttes, on the North Platte, it seems also probable that the same basin continues 

 northward along the slope of tlie Rocky Mountains nearly or quite to the ^U'ctic Sea. 

 Whether or not there are any indications of this formation over the eastern range in 

 the British possessions, I have no means of ascertaining, but the Wind River chain, 

 which forms the main divide of the Rocky Mountain Range, exhibits a great thickness 

 of the lignite tertiary beds on both eastern and western slopes, showing couclusivelj' 

 by the fracture and inclination of the strata, that prior to the elevation of this range, 

 they extended uninterruptedly in a horizontal position across the area now occupied 

 by the Wind River chain. Passing the first range of mountains in the Laramie Plains, 

 we find that the Big Laramie River cuts through cretaceous beds, Nos. 2 and 3, con- 

 tinuing our course Avestward to Little Laramie, a branch of the Big Laramie, and No. 

 3 becomes fifty to one hundred and fifty feet in thickness filled with fossils, Ostrea con- 

 (/esta, and a species of Inoceramus. At Rock Creek, about forty miles west of Big Lar- 

 amie EiA'er, the lignite beds oA^erlap the cretaceous, but in such a way as to show that 

 the more inclined portions liaA^e been swept away by erosion, and that the red beds and 

 carboniferous limestones once existed without break and in a horizontal position across 

 the Laramie Range prior to its elevation. 



I cannot discuss this matter in detail in this article, but the eA'idence.is clear to me 

 now, that all the lignite tertiary beds of the West are but fragments of one great basin, 

 interrupted here and there by the upheaA^al of mountain chains or concealed by the 

 deposition of newer formations. 



When I wrote tlie article on the lignites of the West, .g,ll my own inves- 

 tigations pointed strongly to the conclnsion that no coal beds of any 

 great valne, in an economical i)oint of view, would ever be found in the 

 West in formations older than the tertiary. When my large collections 

 of vegetable and animal remains from the coal beds in Wyoming, Colo- 

 rado, and New Mexico, now deposited in the Smithsonian Institution, are 

 carefully studied, I can speak with more confidence on that point. 1 can 

 say just here that I have as yet seen no reason to change that opinion 

 so far as my own observations are concerned. 



In the spring of 1868, Professor Lesquereux, who is so justly celebrated 

 for his skill in the study of fossil plants, sent me the following valuable 

 notes as the result of a preliminary examination of some leaf impressions 

 from the coal deposits in various parts of the West. His conclusions 

 seem to confirm my opinions that all these coal formations are of tertiary 

 age. 



SPECIES FROM EOCK CREEK, LARAMIE PLAINS. 



1. Populus attenuata, Al. Brauu. The identity of these leaves with the European spe- 

 cies is undoubted. 



2. Populus IcBvigata, sp. nov., related to P. halsamoides, Gopp., a species which, like 

 the former, is abundant in the miocene of Europe. 



