180 GEOLOGICAL SUEYEY OF THE TEREITOEIES. 



At the base of the hilis there is a large boiling sulphur-spring, in which 

 the water is constantly agitated, rising to the height of 3 and 4 feet. 

 It is about 12 feet in diameter and encircled by a collar-like rim, which 

 is beautifully incrusted. It consists principally of silica and sulphur. 

 In the stream proceeding from the spring there is C|uite a deposit of 

 sulphur. The water contains — 



Sulphur, (Yery abundant.) 



Alumina, 



Silica, 



Lime, (trace.) 



Iron, (trace,) 



Chlorine, 



Sulphuric acid. 



Its temperature is 183Jo F. About 300 feet west of this spring there 

 is a steam-jet, which was named the Locomotive Jet from the noise 

 made by the steam in escaping. The temperature there was 191° F. 

 On the sides of the hills there were many more steam-jets, in which the 

 highest temperature attained was 197^° F. To the southeast of the 

 boiling sulphur-spring is a large turbid spring about 35 feet in diameter. 

 Its contents consisted of a xery thin bluish mud containing — 



Sulphate of alumina of iron, 

 Chloride of magnesium, 

 Sulphate of alumina, 

 Free su]i)hur. 

 Silica, 



and having a temi)erature of 1G3" F. It was acid in reaction and tasted 

 strongly of alum. About three hundred yards south from the main 

 spring there is a collection of mud and suli^hur springs. The principal 

 mud-spring in this group contains a thick, blue mud. It has the con- 

 sistency of paint, and the steam, in escaping from it, does so with a 

 thud-like noise, and at times projects the mud to a considerable height. 

 Its temperature is ISSP F. The mud has a strong alum taste, is acid 

 in reaction, and contains — 



Sulphate of iron and alumina, 

 Sulphate of magnesia, 

 Chloride of magnesium, 

 Alumina, 

 Sulphur. 



Kear this latter spring there is another, which was named the Foam 

 Spring. The water is very turbid and, floating on its surface, there is 

 a greenish, sandy, foam-like material consisting of — 



Sulphur, (very abundant,) 



Silica, 



Oxide of calcium, 



Suli)hate of alumina. 



It is in a constant state of agitation. There are many other sulphur 

 and mud-springs here, which resemble one another closely. All the mud- 

 springs are impregnated with alum, and the stream flowing away from 

 the hills is called Alum Creek, the water of which is strongly astringent. 

 The alum is an iron alum. Leaving the hills we found camp, situated 

 on the bank of the Yellowstone Eiver, at a place called Mud Volcanoes. 

 Here again was a large collection of mud and sulphur springs. Imme- 

 diately back of camp were two crater-like mud-springs or volcanoes 

 about 10 feet in depth, at the bottom of which the escai)ing steam kex)t 



