bsduch.] WIND EIVEE EANGE SILUEIAN. 71 



projection of tlieir area will be terminated on the west side by a scalloped 

 line. From west of Camp Brown these Potsdam sandstones extend south- 

 eastward, lying between the base of the second and the western edge of the 

 third chain. Comparatively massive stratification is shown by the group. 

 Narrow interstrata of sandstone showing a highly argillaceous compo- 

 sition produce changes in the weathering of exposed surfaces. In direct 

 contact with the most recent metamorphic granites described from this 

 region, it is not unfrequently a difficult matter to draw the line of sep- 

 aration between the two. Often the junction may be found exposed, and 

 there we see, in certain instances, that the quartzites and granites 

 blend into each other. Similar cases have been observed elsewhere, par- 

 ticularly hi Colorado.* 



It is an evident fact that the same influences which have produced the 

 metamorphism of the underlying granites have transformed the origi- 

 nal sandstones into the Potsdam quartzites. 



So far as could be determined the dip of the sandstones varies from 

 3o° to 12°, its direction being determined by a strike parallel to the trend 

 of the range. About east of Miner's Delight the Potsdam Group is hid- 

 den from sight by overlying beds. Again it appears on the Sweetwater, 

 near what has been designated as the " Little Canon." 



The thickness, of the entire series may be regarded as varying be- 

 tween ISO and 320 feet. In part, this is due to unequal extension of the 

 metamorphosing influences, in part to local thickening of the beds. In 

 coloring, the sandstones exhibit a number of shades, changing from 

 bright red to a dark, rusty brown. Wherever they have been exposed 

 in comparatively isolated masses they have lost some of the coloring 

 matter and are brownish gray, in rare instances even white. 



Organic remains here, as at many other localities where the group is 

 exposed, are limited to a few species. I observed a Lingula (probably 

 L. prima) in considerable numbers, but in a very poor state of preserva- 

 tion. Within the same beds, in the Black Hills of Dakota, Dr. Hay den 

 found (1857) Lingula antiqua, L. prima, and Obolus oppolinus. (°?) Near 

 South Pass, on the Sweetwater, he found (1870) Obolella nana in the 

 same beds. 



Near Camp Baker, Dana and Grinnell collected some fossils in ap- 

 parently the same horizon. Although the palseontological evidence col- 

 lected within this group is meagre at best, it would be sufficient to es- 

 tablish the identity of the series, even were not this made apparent by 

 its relative position. 



Calciferous Group. 



Usually some representatives of the Calciferous Group may be found 

 in connection with the Potsdam. Dr. Hayden, in speaking of the latter 

 series, regards the Carboniferous strata as resting directly upon the Pots- 

 dam. Professor Comstock takes issue with him on this point. He says :t 

 "This, as we shall see, is certainly an error; * * * there are 

 some indications of the thinning out of the Calciferous beds in the neigh- 

 borhood of South Pass, winch would partly justify his opinion." The 

 examinations made by Dr. Hayden upon this point were mainly in the 

 region of South Pass. At that locality the Calciferous beds cannot be 

 recognized. Along the eastern base of the range a number of strata 

 appear that may be referred to this group. Toward the southeast they 

 thin out and entirely disappear before we reach the Little Popo-Agie. 



* Compare Eep. TJ. S. Geol. Surv. 1874, p. 211. 



t Report upon Eeconnaissance of Northwestern Wyoming, 1S73. "Washington, 1874, 

 p. 109. 



