



Ch. XVIL] 



CARBONATED SPRINGS. 



411 





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of Cheshire are the richest in our country ; those of North- 

 wich being almost saturated. There are others also in Lan- 

 cashire and Worcestershire which are extremely rich.* They 

 are known to have flowed for more than 1,000 years, and 

 the quantity of salt which they have carried into the Severn 



and Mersey must be enormous 



These brine springs rise up 



through strata of sandstone and red marl, which contain 

 large beds of rock salt. The origin of the brine, therefore, 

 may be derived in this and many other instances from beds 

 of fossil salt ; but as muriate of soda is one of the products 

 of volcanic emanations and of springs in volcanic regions, 

 the original source of salt may be as deep-seated as that 



of lava. 



Many springs in Sicily contain muriate of soda, and the 



' flume salso,' in particular, is impregnated with so large a 



quantity, that cattle refuse to drink of it. A hot spring, 



rising through granite, at Saint ISTectaire, in Auvergne, may 



be mentioned as one of many, containing a large proportion 



of muriate of soda, together with magnesia and other in- 

 gredients, f 



Carbonated springs. — Auvergne. — Carbonic acid gas is very 



plentifully disengaged from springs in almost all countries, 

 but particularly near active or extinct volcanos. It has the 

 property of decomposing many of the hardest rocks with 

 which it comes in contact, particularly that numerous class in 

 whose composition felspar is an ingredient. It renders the 

 oxide of iron soluble in water, and contributes, as was before 

 stated, to the solution of calcareous matter. In volcanic dis- 

 tricts these gaseous emanations are not confined to springs, 

 but rise up in the state of pure gas from the soil in various 

 places. The Grotto del Cane, near Naples, affords an example, 

 and prodigious quantities are now annually disengaged from 

 every part of the Limagne d' Auvergne, where it appears to 

 have been evolved in large quantities from time immemorial. 

 As the acid is invisible, it is not observed, except an excava- 

 tion be made, wherein it often accumulates, so that it will 



extinguish a candle. There are soi 





springs in this district, 



? 





* L. Horner, Geol. Trans, vol. iii. 



p. 94. 



t Ann. de 1' Auvergne, tome i. p. 234 



