SURVEY OF COLORADO AKD NEW MEXICO. 17 



not tell. This narrow belt, about ten or fifteen miles wide, extending up 

 to the granite rocks, and for the most part concealing all the intermedi- 

 ate rocks, forms a sort of bench, with a gently ascending grade for the 

 Union Pacific railroad. 



Either above or below this bench the ascent to the mountains would 

 have been A'ery difficult, expensive, and perhaps impossible. 



About twenty miles south of Cheyenne a bed of coal has been opened 

 and wrought to som e extent. The outcropping revealed a bed of im- 

 pure coal four feet eight inches thick, with an inclination 12° east. 

 The coal became more valuable as it was worked further into the earth; 

 and by following the direction of the dijp, the coal was found to be five 

 feet four inches thick. In nearly all instances coal beds increase in 

 thickness, rather than diminish, the further they are explored. The 

 whole plain country is covered with such a thickness of superficial drift 

 that it is next to imi^ossible to obtain a connected section of the under- 

 lying rocks. Sometimes a stream will cut so deep that a portion of 

 them is exposed, and by following it a great distance, the order of super- 

 position may be obtained with some degree of correctness. 



A section across the upturned edges of the strata, from the direction 

 of the mountains eastward, is as follows : 



7. Drab clay passing up into areuo-calcareous grits composed of an 

 aggregation of oyster-shells, Ostrea suMrigonalis. 



6. Lignite — 5 to 6 feet. 



5. .Drab clay — 4 to 6 feet. 



4. Eeddish, rusty sandstone, in thin laminse — 20 feet. 



3. Drab arenaceous clay, indurated — 25 feet. 



2. Massive sandstone — 50 feet. 



1. No. 5, cretaceous apparently passing up into a yellowish sandstone. 



The summits of the hills near this bed of coal are covered with loose 

 oyster shells, and a stratum four feet thick, or more, is composed of au 

 aggregation of them. This species seems to be identical with the one 

 found in a similar geological position in the lower lignite beds of the 

 Upper Missouri, near Fort Clark ; also at the mouth of the Judith, and 

 at South Boulder, and doubtless was an inhabitant of the brackish 

 ■waters which must have existed about the dawn of the tertiary x)eriod 

 in the west. It would seem, that in these lower coal beds the molluscous 

 life was almost entirely confined to this genus, (from three to five species 

 having already been discovered.) ISTear Medicine Bow Creek there is a 

 thin seam of oyster shells, quite minute, and at Point of Rocks, on the 

 Union Pacific railroad, above several beds of coal, there is a layer two 

 feet or more iu thickness, made up of the shells of a fine large species, 

 about the size of our common edible oyster. 



On the Upper Missouri a great variety of well-known fresh-water 

 types of shells are found iu the strata connected with the coal, especially 

 toward the middle portion. But southward I have never met with any 

 other shells than oysters, in direct connection with the coal beds. 



During the summer of 1859 1 traced this lignite formation uninter- 

 uptedly from the Upper Missouri Yalley to a point on the Korth Platte, 

 about eighty miles northwest of Fort Laramie. It is there overlapped 

 by the modern tertiary deposits previously described, but reappears 

 about twenty miles south of Cheyenne, and extends with some inter- 

 ruptions far southward into New Mexico. During the summer of 18G8 

 I traced these coal beds, on the other side of the mountains, westward 

 nearly to Salt Lake City ; and in the Middle and South Parks there are 

 quite extensive developments of them, 



I make these remarks as confirmatory of a statement which I made 

 2 GS 



