bsduch.] ECONOMIC GEOLOGY LIMESTONES, &C. 149 



eompact coke. These are preferred for smelting and other processes. 

 In my report on the coal region of Evanston I shall have occasion to 

 enter into the details of composition and economic utility of these coals 

 more fully than could here be done. 



LIMESTONE. 



On the eastern slope of the Wind Eiver Mountains, in the Sweetwater 

 and Seminole Hills and near Kawlings, limestones are abundant. At 

 the first-named locality the admixture of silica generally renders them 

 impure, but some strata can be found that are comparatively free from 

 it. Within easy reach of the settlements, these beds may at some future 

 time prove serviceable. Excepting the silica, they are sufficiently pure 

 and almost quite free from alumina. Within the same regions some beds 

 may be found that could be utilized as marble. They occur near the 

 base of the Carboniferous series. In the Sweetwater and Seminole Hills 

 the limestones show essentially the same characteristics, but contain, 

 perhaps, less silica. On the eastern slope of Eawlings Peak strata com- 

 posed of this material occupy a very prominent position. I am informed 

 that some lime is burned in that vicinity, and that the quality obtained 

 is good. Along the western slope of the range and south of the Sweet- 

 water Hills limestones occur, but they are very impure, approaching 

 more closely in character calcareous shales. 



GYPSUM. 



This mineral occurs most abundantly in the lower portion of the Tri- 

 assic beds. Below the junction of Twin Creek and the Little Popo-Agie 

 I noticed the most extensive exposures. Beds were there found reaching 

 a thickness of several feet. Generally this gypsum is light red, gray, or 

 yellow, but white strata can be found. It is crystalbne rather than com- 

 pact, resembling alabaster in texture. Some of the beds would furnish 

 excellent material for purposes of carved ornamentation. Fibrous gyp- 

 sum (satin-spar) is found together with the other, occurring in narrow 

 seauis and veins cutting across the strata. As gypsum is essentially a 

 local deposit, the thickness of the beds varies considerably at different 

 localities. Near the Popo-Agie settlements, however, there is an ample 

 supply for all purposes. Throughout the formations composed in a 

 great measure of shales we find crystals of selenite. Mostly they are 

 quite small, but they occur in tablets of several inches in thickness and 

 a foot in diameter. Among all others, the Wasatch Group may be re- 

 garded as the one most highly favored in this respect. 



CEMENT. 



Many of the shales and marls which occur in the Cretaceous and Ter- 

 tiary Groups would answer very well for the manufacture of ordinary 

 and hydrauMc cement. Within the Sweetwater Group there are some 

 strata that could be used for these purposes with but slight preparation. 

 Many of the marls are arenaceous, but if such were selected that are 

 comparatively free from sand they could be utilized. It is not probable 

 that ever any very great demand for cements will arise in that section 

 of country, and the expenses of transportation would most likely prove 

 to be too heavy to realize profits by shipment. It is well, however, to 

 know that the materials are at hand to render the inhabitants independ- 

 ent in the matter of cements, which often may become an important 

 question. 



