April 14, 1911] 



SCIENCE 



563 



tion of the deposited sediment is every- 

 where much the same, its external habit 

 varies with the manner of its secretion, 

 which may have happened in several ways. 

 It may have been caused by precipitation 

 on relief of pressure, precipitation on 

 cooling, separation by evaporation, and 

 assimilation by algte. Mr. Walter H. Weed 

 has shown conclusively the important part 

 such organisms perform as geological 

 agents in the accumulation of sinter de- 

 posits.^ 



The volume of siliceous alkaline waters 

 far exceeds those of the acid type. On the 

 other hand, the latter occur more widely 

 distributed, are more complex in their 

 composition, and consequently more varied 

 in their deposits. These acid waters come 

 to the surface through fumaroles, solfa- 

 taras, and the so-called mud springs and 

 paint pots. In nearly all such occurrences 

 the waters carry either free hydrochloric 

 or sulphuric acid. In general these 

 thermal waters, which rise throiigh narrow 

 seams and rifts, run but little water and 

 leave behind only thin incrustations 

 around the sources of supply. These de- 

 posits are found widespread over the park 

 and consist principally of sulphates of 

 alumina and double compounds of alumina 

 and iron. While they show a mingling of 

 saline compounds carrying more or less 

 silica as an impurity, the number of min- 

 eral species remains singularly few. Halo- 

 trichite, alunogen, and alum are the only 

 minerals of the alum group determined. 

 In the far more arid regions of New Mex- 

 ico accumulations of these minerals have 

 been described by Dr. C. W. Hayes" as de- 



' Walter H. Weed, " Formation of Travertine 

 and Siliceous Sinter by the Vegetation of Hot 

 Springs," U. S. Geol. Survey, Ninth Ann. Kept., 

 Washington, 1890. 



»Dr. C. W. Hayes, Bull. U. S. Geol. Survey, 

 No. 315, pp. 215-223, 1905. 



posits 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 re- 

 stricted in quantity. Scorodite, delicate 

 crystals of sulphur, and ochreous deposits, 

 mainly ferric oxide and silica, are char- 

 acteristic of certain acid and neutral 

 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 decompo- 

 sition. 



GASES FROM THERMAL SPRINGS 



Several years ago gases emitted from 

 many of the springs were collected and 

 submitted to analysis by Professor F. C. 

 Phillips of Pittsburgh. 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 char- 

 acterized by carbon dioxide, one analysis 

 from the spring upon 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 sulphur spring in the Mammoth 

 Hot Spring Basin, and the other from the 

 Shoshone Geyser Basin. In none of the 

 waters from the geysers and large hot 



