STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 85 



and by Fenneman,^- who assign to it a thickness of 800 to 1,200 

 feet. These observers recognized no coal in the Fox Hills, as they 

 took the important coal seams of the basin to be Laramie. But 

 Stevenson^^ saw coal in rocks of Fox Hills age at 5 miles southeast 

 from Evans, about 40 miles north from Denver. From a sand- 

 stone overlying coal he obtained Ammonites lobatus, Cardium 

 speciosmn, Mactra alta^ Mactra warrcniana, Lunatia nwrcaucnsis 

 and Auchura. The Halyiiienites is abundant. 



The deposits in western Wyoming, which earlier observers 

 termed Fox Hills, are known now to belong to the Pierre, but the 

 formation is present in some areas. The " Laramie " in the north- 

 eastern part of the Bighorn Basin, 150 to 700 feet thick, is appar- 

 ently Fox' Hills. It is mostly a massive sandstone but contains 

 some seams of coal, occasionally workable though of quality in- 

 ferior to that from older formations. East from Bighorn Moun- 

 tains, the Fox Hills was recognized in the Lost Spring field by 

 Winchester, in the Sussex field by Wegemann and in the Black 

 Hills by Darton, but no coal is reported from any locality, except 

 one, where Wegemann saw a deposit of *' unusual variability in 

 thickness .and quality."^* 



The Fox Hills is known in northwestern Montana as the Horse- 

 thief sandstone described by Stebinger, as the Lennep sandstone of 

 Stone and Calvert in the central part of the state. Stebinger traced 

 the Horsethief sandstone across the Canadian boundary and proved 

 its continuity with the Fox Hills of Dawson. He describes the 

 sandstone as. 360 feet thick, bufl:', coarse, massive and much cross- 

 bedded in the upper half, but becoming slabby and more or less 

 shaly toward the base. Usually the fauna is brackish, Ostrea, Cor- 

 hiciila, Corhida, and Auomia, but at some horizons it is marine of the 

 litoral type, Tancredia, Cardium and Mactra. In his paper of 1914, 

 he shows that the Horsethief sandstone was at one time continuous 

 from the Teton district at eastern foot of the Rocky Alountains to 



^-' G. H. Eldridge, Mon. 27, 1896, pp. 69, 72, -/i; N. H. Fenneman, Bull. 



265, 1905, p. 2>2,- 



53 J. J. Stevenson, Amer. Journ. Set., Vol. XVII., 1879, pp. z^<^ZT2- ■ 

 5*C. W. Washburne, Bull. 341, p. 169; D. E. Winchester, Bull. 471-F, 



1912, p. 58; C. H. Wegemann, the same, pp. 25, 32; N. H. Darton, Prof. Paper 



65, 1909, p. 57. 



PROC. AMER. PHIL. SOC. , VOL. LVI, G, MAY 23, I917. 



