70 Natural History of Volcanos and Earthquakes. 



where, in consequence, the penetration of meteoric water into 

 the interior of our earth has been rendered possible, and where 

 natural hydraulic tubes have been formed by the upraising of 

 strata, there the phenomena of thermal and mineral springs were 

 the consequence. 



We should transgress our limits, were we here to pursue the^ 

 subject of thermal springs in their chemical relations, since the 

 general aim of these remarks is to show that their degree of heat 

 depends on the greater or less depth of their origin, consequently 

 wholly and solely on central heat. The following remarks, how- 

 ever, upon their chemical constitution, may perhaps not be en- 

 tirely superfluous. 



The chemical ingredients of those springs which take their 

 origin at the boundary between volcanic and Neptunian forma- 

 tions, are derived in some springs from the former, in others from 

 the latter formations, in others again from both. The following 

 conjecture is probable. If considerable quaiitities of carbonic 

 acid gas are disengaged from the interior, which are absorbed 

 under strong hydrostatic pressure by the water, and thus act on 

 the volcanic stone, decompositions ensue. The alkalies which 

 are found in all stony masses of igneous origin, are extracted by 

 the carbonic acid, and taken up by the water as carbonate of al- 

 kalies, and especially carbonate of soda. In the same manner 

 are formed the bicarbonates of lime, magnesia, and of protoxide 

 of iron. Metallic chlorides and sulphates may perhaps be less 

 frequently derived from volcanic matter, and more so from the 

 Nepthnian formations. In this matter probably, are formed the 

 great number of springs, which rise in the neighborhood of basal- 

 tic hills. Where there is no disens:a2:ement of carbonic acid gas 



O'^O 



from the interior, no such mineral springs are found ; at least we 

 cannot assume that in this case the volcanic rock contributes any 

 thing essential to the constituents of the springs. Thus, prob- 

 ably^ neither in the Pyrenees nor Alps do the springs take up any 

 thing essential from these rocks. The circumstance, that springs 

 of very various chemical composition arise in the vicinity of the 

 granite of different mountains, might here serves as an indirect 

 proof. At the same time, the nearly similar composition of 

 the springs occurring in the neighborhood of the basaltic cones, 

 where carbonic acid gas is disengaged, however different may 



