214 THE CAMBRIAN. [bull. 81. 



Ill his report on the geology of the Wind River district, made in 1883, 

 Prof. St. John describes the geology of the Gros Ventre Range, accom- 

 panying it with two plates of sections across the range at various 

 points. 1 On the map accompanying the volume the geographic distri- 

 bution of the strata referred to the Silurian is delineated. He also 

 describes the out-crops of the strata on the northwestern and north- 

 eastern sides of the Wind River Range, that he refers to the Silurian. 2 

 Reference to Prof. St. John's sections will be made in describing the 

 Cambrian rocks of the Wind River and Gros Ventre Ranges. 



On the map accompanying the twelfth annual report of the Hayden 

 survey, issued in 1883, the geographic distribution of the strata referred 

 to the Silurian in the Sweetwater Range, the Wind River Range, the 

 Gros Ventre Range, and the Teton Range is shown. The Silurian in- 

 cludes the quartzite referred to the Potsdam, the Cambrian limestone 

 referred to the Lower Quebec by Prof. St. John, and the Calciferous 

 referred by him to the Upper Quebec. This map was compiled from the 

 work of Messrs. Peale, St. John, and Endlich. There is also a special 

 map showing the district reported on by Prof. St. John in 1883. 



DAKOTA. 



The presence of evenly bedded sandstones about the Black Hills was 

 noted as early as 1822 by Dr. Edwin James, who represented them 

 upon a diagrammatic section, extending irom the Alleghany to the 

 Rocky Mountains. He undoubtedly confused the sandstones of the 

 Trias with those of the Cambrian ; but it is one of the earliest recorded 

 illustrations of the mode of occurrence of the sandstone in this region. 

 That he did not penetrate to the interior portion of the hills is evident, 

 as his section represents the sandstone extending in level horizontal 

 layers entirely across the area occupied by them. 3 



In 1856 Mr. H. Engelmann published a description of the rocks of the I 

 Black Hills. The strata next to the granitic nucleus are described as 

 tC more or less altered sandstones and limestones, dipping in various 

 directions and degrees. Most of the sandstones are fine grained,, light 

 yellowish red, and do look much like metamorphic, but some show the 

 transition into a siliceous rock." 4 Not far from camp 56 he found a 

 friable sandstone made up of coarse square grains of granite, appar- 

 ently deposited after the formation of the igneous rocks. Near camp 

 58 the sandstone is light yellowish red and tine grained. There is also 

 a gray variety, above which is a layer of a dark red sandstone, coarse 

 grained, soft, and highly micaceous. 5 This is the sandstone in which 

 Dr. Hayden subsequently found the Upper Cambrian fauna. 



'Report on the geology of the Wind River district. U. S. Geol. Surv. of the Terr., 12th Annual 

 Report, 1883, p. 208. 

 2 Op. cit., pp. 251-253. 



3 Geological sketches of the Mississippi Valley. Phil. Acad. Sci., Jour., vol. 2, pt. 2, 1822, pp. 326-329. 



4 Report of a geological exploration from Fort Leavenworth to Bryan's Pass, made in connection with 

 the survey for a road from Fort Riley to Bridger's Pass, under Br j an. Rept. Sec. of War, Appendix II, 

 1856, p. 508. 



6 Op. cit., p. 510. 



