exdlich.] SOUTHEEN AREA— WASATCH GROUP. 127 



some difference exists. The latter determined the composition as fol- 

 lows: 



Per cent. 



Volatile matter 48.00 



Fixed carbon 50.57 



Ash 1.43 



100. 00 



Comparing these with the mean average taken from 34 analyses of 

 Colorado coal, we find a striking constancy of the percentage of fixed 

 carbon : 



Per cent. 



Water , 6.43 



Fixed carbon 52.51 



Volatile matter 34.09 



Asb .- 6.83 



It is a matter of experience that different banks of coal, thongh occur- 

 ring in the same horizon, frequently vary considerably as to the quantity 

 of ash they contain. It is due to more or less accidental admixtures, 

 and frequently to inclusions of clay and gypsum between the narrow 

 seams which traverse nearly all of the younger coals. 



Besides these two "fields" we find no further outcrop of the Laramie 

 Group in our district. An enormous amount of coal that may be utilized 

 at some future time is stored within this area. At present, so abundant 

 a supply is offered at the most advantageous localities that it may be 

 centuries hence before the treasures of this section will be sought after.* 



TERTIARY. 



Wasatch Group. 



Directly overlying the upper sandstones of the Laramie Group, we 

 find an extensive series of sandstones, shales, and marls, which form the 

 Wasatch Group. The most extensive section of the entire group may 

 be obtained north of Salt Wells. Passing down along the northward 

 sloping Laramie beds, we find a heavy mass of variegated marls overly- 

 ing some shales and sands. Conformable with the underlying strata 

 these dip northward at a diminishing angle. Deep caiions are cut into the 

 marls, and some very grotesque forms are carved out of them by erosion., 

 They present a very handsome variation of coloring. Eed, brown, and 

 maroon strata alternate with white, yellow, and greenish ones. Isolated 

 strata of sandstone are found at several horizons. As a rule, the marls 

 are highly arenaceous ; but some strata can be found which are free 

 from sand. At the base of these marls accumulations of conglomerate 

 may be found at some places. The upper portions of the Wasatch 

 Group are formed by yellow and brown shales and loosely-cemented 

 sandstones. Some of the latter contain numerous siliceous concretions, 

 which appear in the form of chalcedony and agate. In the upper sand- 

 stones and shales we find a number of Carbonaceous layers and some 

 small seams of coal. 



Passing over some rusty sandstones, we finally reach the base of the 

 Green Eiver series. At the point of greatest development which we 

 observed, the lower marls reach a thickness of 600 to 700 feet. I regard 



* Note. — In my report upon tbe coal-beds of Evanston, which is in preparation, I 

 shall have occasion to enter into the interesting geological questions connected with 

 the Laramie Group, as -well as into the economic value of the various "liguitic" 

 coals. — E. 



