GASES FROM THERMAL SPRINGS 117 



compounds carrying more or less silica as an impurity, the number of 

 mineral species remains singularly few. Halotrichite, alunogen, and 

 alum are the only minerals of the alum group determined. In the far 

 more arid regions of New Mexico accumulations of these minerals have 

 been described by Dr. C. W. Hayes® as deposits from aqueous solutions 

 associated with igneous rocks. 



Under quite different conditions, and as thin layers deposited below 

 water level in the Norris Basin, occur incrustations of both sulphides of 

 arsenic, orpiment and realgar. They are, however, very restricted in 

 quantity. Scorodite, delicate crystals of sulphur, and ochreous deposits, 

 mainly ferric oxide and silica, are characteristic of certain acid and neur 

 tral waters. These sediments and incrustations point clearly to different 

 conditions of thermal activity. In strong contrast from those described 

 in connection with siliceous alkaline waters, they indicate an earlier stage 

 in the development of rock decomposition. 



Gases from thermal Springs 



Several years ago gases emitted from many of the springs were col- 

 lected and submitted to analysis by Prof. F. C. Phillips, of Pittsburg. 

 They were all found to carry carbon dioxide, oxygen, hydrogen, and 

 nitrogen, but to vary greatly in relative amounts. In general, those from 

 Mammoth Hot Springs, where the waters issue through limestones, are 

 characterized by carbon dioxide, one analysis from the spring on the main 

 terrace holding no less than 98.68 per cent of the gas. Those from the 

 upper basin, which issue directly from the rhyolite, consist principally of 

 nitrogen, the Artemesia Geyser carrying 95.08 per cent of the latter gas. 

 Traces of methane were found in several waters. Hydrogen sulphide was 

 only detected in two samples, and in neither of these did the gas amount 

 to one per cent of the gaseous content. One of these was from a sulpliur 

 spring in the Mammoth Hot Spring Basin and the other from the Sho- 

 shone Geyser Basin. In none of the waters from the geysers and large 

 hot springs in the three principal basins was any hydrogen sulphide 

 detected. 



Professor Phillips says : *'There is, in fact, a curious gradation between 

 analyses from No. 1 and No. 10, as regards the proportion of nitrogen 

 and carbon dioxide. Oxygen is present in all of them, and as ten of 

 these gases contain combustible elements, hydrogen and methane, it is 

 evident that the gas as it escapes from the spring has not been exposed to 

 a high temperature." 



It is admitted by most authors that under certain conditions all these 



« Dr. C. W. Hayes : Bulletin of the U. S. Geological Survey, No. 315, 1905, pp. 215-223. 



