SODIUM. 439 



waters. Besides direct observations on tliis [)()iiit, it is a well known fact 

 that below the permanent water-level of a country redncing agencies are at 

 work, so that the heavy metals occur as sulphides and the clays are coni- 

 monlv tinted blue from tlie presence of ferrous compounds. Of course sedi- 

 mentary rocks of all ages also retain carbon, sometimes in large quantities, 

 as graphite, coal, i)etroleum, etc , so that reducing matter is provided at all 

 dejjths to which sedimentary strata extend. ( )rganic matter is also said to 

 be present in hot springs issuing from granite. In some cases granite un- 

 doubtedly overlies sedimentary rocks and some granites are beyond ques- 

 tion metamorphic. It appears to nu^ possible, however, that some hot 

 springs issuing from granite and seeming to carry organic matter do not 

 really bring such compounds to the surface ; for at Steamboat Springs, in 

 spite of the very high temperature of the water, living organisms of low 

 forms are abundant and grow luxuriantly close to the vents. A description 

 of the circumstances has been given in the chapter on that localit}-. 



Solvents probably independent of carbon. SiuCe silicateS of tllC alkalis aud tllG 



earths are decomposed by carbonic acid and by hydrogen sulphide, the hy- 

 pothesis that these reagents are due to the interaction of soluble sulphates 

 and organic matter, more or less metamorphosed, affords a method of ac- 

 counting for the existence of solvents for the ores. It is by no means cer- 

 tain, however, that the conditions are thus adequately explained. In his 

 great memoir on the Icelandic geysers, Bunsen^ called attention to the fact 

 that in gases evolved by the help of organic matter, either in nature or by 

 artificial processes, hydrocarbons are almost invariably present. In a very 

 large part of the volcanic emanations, both gaseous and fluid, on the other 

 hand, hydrocarbons are wholly wanting. Hence he concludes that in these 

 cases the sulphur and hydrogen sulphide are in no way dependent upon 

 organic matter. Prof. H. Credner" believes that most of the gases emanat- 

 ing from volcanoes, including sulphurous acid and hydrogen sulphide, are 

 disengaged from the fluid interior of the earth in which they have existed 

 since the original formation of the globe. Professors Tscdiermak' and 

 E. Reyer* hold similar views. From the point of view of the nebular hy- 



' Poggendorff, Annalen, vol. 83. " Neues Jahrbiicb fiir Mineral., 1877, p. 857. 



"■ Elemente tier Gcol., 1887, p. 170. ■" Fysik iler Eriiptionon, lf^87. 



