330 GEOLOGICAL SUEVEY OF THE TEREITOEIES. 



side upon the granite, is a local variation of the yellow and light-brown 

 usually found in Cretaceous IsTo. 1. A section running east to west will 

 give a better idea of the arrangement of the strata in this locality, 

 Eesting upon the granite («) we find the mentioned red-brown sand- 

 stone {b) underlying a white one, which in turn again is covered by a 

 brown ; between the western slope of this bluff and the rise of another 

 one, a white limestone {e) occurs, overlaid by a white, shaly limestone, 

 with Inoceramus^ forming the apex of a low bluft", and dipping westward 

 at an angle of about 10°. It is covered by white sandstone and a light- 

 greenish shale, (*.) A yellow to light-brown sandstone (fc) finishes the 

 western extent of the valley. Cretaceous waters have probably never 

 intruded far inland to the west in these localities, as at present no trace 

 of them is found, unless coming either from the north or the south. 



At this place, between the Cretaceous and the succeeding Tertiary, 

 the Lignitic formation may find its position. As the entire district of the 

 San Luis division shows a good development of these Lignitic beds at 

 but one point south of Canyon City, and the opportunity for making 

 detail-studies of the geological relations of this group did not offer, I 

 take the liberty of referring to Mr. Marvine's report for observations re- 

 garding its age and relative position, and also to Professor Lesquereux's 

 work. A section will show the position of the coal-beds. The foot-wall 

 is formed by white, middle-grained sandstone, upon which a coal-bed, 

 varying from 3|^ to 5 feet, rests, which is separated from a narrow seam 

 of 1 foot to 16 inches by a stratum of gray shale, of 10 to 14 inches in 

 thickness ; 60 feet of grayish-brown argillaceous shales, with small par- 

 ticles of mica, follow, containing indistinct remains of plants, terminated 

 by a narrow coal-seam, above which 45 feet of the same shale follow, in- 

 tersected by two similar thin seams of coal. Fifteen feet of yellowish 

 sandstone rest upon this, separated from the overlying 25 feet of white 

 sandstone, which form the top of the bluff, by a thin stratum of shale. 

 The three upper seams are not used, but the lower ones are worked 

 for coal by the Denver and Rio Grande Railroad Company. Canyon 

 City coal-mines is the usual appellation given to these deposits. A 

 tunnel has been run in on the main vein in a southerly direction for the 

 distance of about 1,400 feet, and drifts from this serve to work the coal, 

 of which both the 4 foot bed and the 1-foot seam are utilized. The main 

 bed dips at an angle of 2° to 4° to the westward, remaining constant in 

 this as far as worked thus far, but to judge from the stratigraphy 

 exposed on the surface, this dip will change farther west, reversing its 

 direction. At the time of my visit, Sei^tember, 1873, the mines had 

 been worked for fifteen months, and, according to a statement kindly 

 furnished by Prof. R. N. Clark, at Labran, Col., the production of the 

 mines in 1872 was 4,956 tons, to 12,909 produced in 1873. Mineralogi- 

 cally considered, the coal would be termed a compact bituminous coal. 



From all that could be learned with reference to the relative position 

 of the larger coal-vein mentioned a*>ove, it seems that those worked 

 farther eastward are underlying it. Probably beginning with the first 

 rising sandstone bluff's, a little east of the coal-mines, we find the Ter- 

 tiary formation. As in section a, our investigations did not carry us 

 through the Tertiary portions of the beginning plains for a length of 

 time sufficient to make careful comparisons, and consequently to admit 

 of strict and correct discrimination. It is quite likely, however, that 

 the higher bluffs, composed of a yellowish and brownish sandstone, ris- 

 ing up beyond the light-colored and gray shales, should be ascribed to 

 the Tertiary period. As far as could be observed, no unconformability 

 exists between them and the underlying strata, although it dare not be 

 denied that any such existing unconformability would have been greatly 



