78 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



We notice, occasionally, in this region, as well as farther west, tliat some 

 of the Carboniferous strata contain impregnations of pyrite. A decom- 

 position of this mineral, together with such changes to which the adjacent 

 rocks would necessarily be subjected, wUl generate a considerable amount 

 of heat. I consider it probable that the former cave, which occurs near 

 the springs, at one time contained a reservoir which supplied the latter. 

 It is possible that at the present time another one exists, still intact, 

 therefore not revealing its presence. This view receives some support 

 from the fact that the nearer spring is the hot one, while the other, 

 though showing the same composition and passiag through the same 

 kiad of rocks, is cold. 



A section given with the succeeding pages will easily render clear what 

 has been said with reference to the stratigraphical features of the pre- 

 cedmg groups. They present a highly interesting iield for study, one 

 to which an entire season could be far more appropriately devoted than 

 a few weeks. 



Permian Group. 



Wherever the Permian group has been observed in the West," its defi- 

 nition as such has been a matter of more or less difficulty. A want of 

 characteristic fossils and the sporadic appearance of the series has had 

 to be contended with. So far as any identifications have been made 

 which are entitled to consideration, we find that Permian strata occur 

 in Kansas, Colorado, and the Northern Territories. Meek and Hayden 

 have obtained fossils from the beds, and regard the determination of the 

 beds containing them as established. It may be regarded as a rule that 

 the group comprises mainly yellow and red sandstones and shales with 

 some dolomites. In case these exhibit but a slight thickness, they may 

 frequently be overlooked and added to the massive red beds generally 

 overlying them. 



Descending the eastern Carboniferous slope of Twin Peak, we reach a 

 low valley trending about northwest to southeast. We find, ux3on exam- 

 ination, that a portion of the slope is composed mainly of reddish and 

 yeUow sandstones, interstratified with shales. Within the shales we see 

 thin banks of hard, crystalline dolomites, and higher up there are thin 

 banks of gypsum. The summit of each little ridge is formed by a hard 

 sandstone, sometimes quartzitic. Atmospheric action has bleached some 

 of the rocks, and they show piak, light yellow, and even white colors. 

 Taking this series of strata, which is closed by a massive bed of white 

 to light yellow sandstone, as a whole, we find that its main bulk is made 

 up of sandstones. Generally these are thinly stratified, containing nar- 

 row beds of yellow, pink, and gray shales between them. The group 

 rests directly upon the hard blue Carboniferous limestones, and is covered 

 by the red beds of Mesozoic age. Estimating the thickness of the group 

 near this locality, we may regard it as about 250 feet. Within these limits 

 are confined the strata which I refer to the Permian. 'No fossils were 

 found within them, except a few indistinct remains of plants. Dr. Hay- 

 den has mentioned, in speaking of the Permian of Kansas, that there 

 the upper two or three hundred feet of the group are probably " on a 

 parallel with the Permian of Europe." In oase tyi)ical Carboniferous 

 fossils extended upward into this series, we would probably have found 

 them, and I am inclined to thiuk, therefore, that they are wanting. 

 Probably only a very limited flora, with perhaps a few invertebrates, 

 existed at this region, and but a small number of the specimens were 

 preserved. 



Following this outcrop of Permian to the southward we find that it 



