86 



EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



fonncl of sufficient thickness near the Big Popo-Agie. The upper termi- 

 nation of this group is formed by thinly bedded, micaceous and argilla- 

 ceous sandstones covered by a thick stratum of the same material. We 

 may regard about 500 feet as the total thickness of this group. FossUs 

 are very scarce, consisting in Inoceramus and some poorly preserved 

 ]ilauts, so far as we could determine. 



Beginning north of the Little Popo-Agie the Fox Hills series can be 

 found to extend northward in a broad band, reaching beyond Camp 

 Brown. It is but slightly affected by the anticlinal upheaval, although 

 its connection eastward is thereby broken. East of Sheep Mountain the 

 group sets in after we have reached the typical bluff country. As indi- . 

 oated in Section II, it dips gently toward the northeast (o), gradually 

 assuming a horizontal position. After forming a prominent row of bluffs 

 and several smaller ones, it is hidden beneath younger P.ost-cretaceous 

 and Tertiary strata. 



About 2 miles west of Camp Brown we find a very interesting hot 

 spring, rising in the beds of this grouiD. It is known as the Hot Sulphur 

 Spring. Within an elliptic basin, 315 feet long and 250 feet wide, the 

 bright green and blue water is contained. A constant bubbling up of 

 carbonic-acid gas gives it the appearance of boiling. So far as deter- 

 mined, the mineral constituents held in solution by the water are iron, 

 lime, magnesia, soda, and potash. They seem to be contained in the 

 form of sulphates, carbonates, and chlorides. Eor the bather the water 

 is very warm, and a stay of only a few minutes will suffice to satisfy aU 

 desire for a warm bath. From a report furnished by Dr. T. G. Maghee, 

 U. S. A., post-surgeon at Camp Brown, to Dr. Heizmann, U. S. A., I 

 extract the subjoined tables of temperatures.* 



* Eej). Eec. Northwestern Wyoming, Capt. Jones, 1873. Washington, 1874, p. 187» 



