408 



SULPHUREOUS AND GYPSEOUS SPRINGS. 



[Cn. XVII. 



I have already endeavoured to explain (p. 403), when speak- 

 ing of the travertin of San Filippo, how the spheroidal masses 



i 



may 



Sulphureous and gypseous springs. — The quantity of other 

 mineral ingredients wherewith springs in general are im- 

 pregnated is insignificant in comparison to lime, and this 

 earth is most frequently combined with carbonic acid. But 

 as sulphuric acid and sulphuretted hydrogen are very fre- 



sum 



posited largely in certain seas and lakes. Among other 

 gypseous precipitates at present known on the land, I may 

 mention those of Baden, near Yienna, which feed the public 

 bath. Some of these supply singly from 600 to 1,000 cubic 

 feet of water per hour, and deposit a fine powder, composed 

 of a mixture of sulphate of lime with sulphur and muriate 

 of lime.* The thermal waters of Aix, in Savoy, in passing 

 through strata of Jurassic limestone, turn them into gypsum 

 or sulphate of lime. In the Andes, at the Puenta del Inca, 

 Lieutenant Brand found a thermal spring at the temperature 

 of 91° Fahr., containing a large proportion of gypsum with 



o 



t Many 



neral springs of Iceland, says Mr. R. Bunsen, deposit gyp- 



X 



same 



It may, indeed, be 



mineral 



before stated, dissolved in hot springs agree very closely with 

 those which are disengaged in a gaseous form from the craters 

 of active volcanos. 



Siliceous springs. — Azores. — In order that water should 

 hold a very large quantity of silica in solution, it seems ne- 

 cessary that it should be raised to a high temperature. § The 

 hot springs of the Valle das Fernas, in the island of St. 

 Michael, rising through volcanic rocks, precipitate vast 

 quantities of siliceous sinter. Around the circular basin of 

 the largest spring, which is between twenty and thirty feet 



diameter 



* C. Prevost, Essai sur la Constitu- 

 tion Physique du Bassin de Vienne, 

 p. 10. 



f Travels aeross the Andes, p. 240. 

 \ Amialen der Chem. 1847. 

 Daubeny on Volcanos, p- 222. 



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