PEALE.I SHOSHONE GEYSEE BASIN SULPHUK HILLS. 271 



SULPHUR HILLS. 



Between Shoshone Creek and the shore of the lake there is a duster 

 of hills cut by numerous ravines, especially towards the north, where 

 they assume crater-like forms, and to a casual observer might appear 

 to be the remains of old volcanic craters. The hills rise from 80 to a 

 100 feet or more above the level of the lake, and are well wooded. The 

 hollows are occupied by mud springs, sulphur pools, and steam vents, 

 which seemed to be in the last stages of action, although this appearance 

 may be due to the lack of water in abundance. The rocks of the hills 

 are conglomerates and sandstones, made uj) of particles of obsidian or 

 pitchstone and geyserite pebbles. In places the sandstones had a vit- 

 rified appearance, due in all probability, as Professor Bradley has sug- 

 gested,* to the slow percolation of the spring waters through the sand 

 while it was beneath the surface of the lake at points other than those 

 of most active ebullition. 



Toward the south the hills are more plateau-like, and the springs and 

 vents are found in the gulches leading towards the lake shore. Korth 

 of the groups shown on the map there are gulches with vents and un- 

 important springs not shown on the accompanying map, but indicated 

 on the map in the report for 1872, which is on a smaller scale, and in- 

 cludes more of the surrounding country. 



The rocks in the hills and hollows are reddish in hue, looking as though 

 they had been subjected to the action of fire. This is due to their dis- 

 integration and the oxidation of the contained iron. This disintegration 

 is due partly to the action of the springs and partly to atmospheric influ- 

 ences. Professor Bradley, in the report for 1872, speaking of the hol- 

 lows, says: "It becomes evident that they have been hollowed out of the 

 surrounding sandstone by the action of the hot springs themselves, 

 which have disintegrated and removed portions of the standstone and 

 conglomerate of the old lake-terrace. Worn bits of rock, i)enetrated by 

 numerous small irregular holes, are abundant on all the lower parts of 

 the slopes, as weU as about the existing vents, showing that the process 

 is still going on." 



In cataloguing the springs found in the Sulphur Hills, I have divided 

 them into two groups, viz. Sulphur Hills Group and the Shore Group. 



The Sulphur Hills Group is seijarated from the Little Giant Group 

 by three hills, 40 to 50 feet high, and occupies a basin of about the same 

 level as the Little Giant Group. The springs are mainly turbid alum 

 springs and mud holes, which are evidently affected by the state of wat^r 

 supply. Many that were mere steam vents when examined by us, must 

 be boiling and sputtering pools when they are supplied with water. 



On the side of the hill north of the main part of the group there are 

 sulphur-lined steam vents, and on breaking the crust beautiful crystals 

 are found. The Shore Group includes the springs that are found along 

 the edge of the lake. These are really divisible into two subgroups, 

 but none of the springs are at all important. 



North of the springs numbered in the group are two small gulches, 

 with steam vents and sulphur holes at their heads. The location of 

 the springs will be rendered clear by a reference to the map. 



* Eeport U. S. Geological Sui-vey, 1872, p. 247. 



