REPORT ON MINERAL AND THERMAL WATERS. 71 



The carbonic acid, which is so frequent an accompaniment of Origin of 

 thermal waters, is explained by Bischof *, as deriving its origin Ji'^^^''^'|J°' 

 from the calcination of earthy carbonates by the heat beneath ; evolved 

 and to this view there seems to be no objection, provided only from 

 we admit, that a portion of water is present, without which, sp""ss. 

 as Faraday has shown, no disengagement of carbonic acid would 

 take place under the influence of even a great heat. 



But that the amount of carbonic acid emitted bears some re- 

 lation to the igneous or eruptive agency heretofore exerted, will 

 appear by a mere enumeration of the localities in which this gas 

 most abounds. 



Passing over its copious emission in the neighbourhood of 

 active and extinct volcanos, I may notice the observations of 

 Hoffman f, who has stated, that the carbonic acid so abundantly 

 evolved at Pyrmont, rises out of what he describes as a circular 

 valley of elevation, caused by the heaving up of the rocks in all 

 directions round this central point. 



Sometimes also the evolution of carbonic acid is connected 

 with faults, as has been observed by Professor Phillips with re- 

 spect to the carbonated or petrifying springs of Yorkshire J. 



So general indeed is the distribution of calcareous rocks in 

 the older, as well as the more modern formations, that I do not 

 see the force of the objection started by Berzelius to the chemical 

 theory of volcanos, in a notice with which he some years ago 

 honoured the work I had published on that subject §, in which 

 he says, that it fails in accounting for the extrication of carbonic 

 acid gas, as a consequence of volcanic action. 



For my own part, inasmuch as an intense degree of heat is the 

 immediate effect of these operations, and as rocks containing 

 carbonic acid in a fixed state are so generally diffused, I should 

 conceive that the extrication of this gas would have been anti- 

 cipated to be a natural result of the process ; unless, indeed, by 

 those theorists, who, maintaining the contrary hypothesis in its 

 simplest form, refuse even to admit that water has had any ne- 

 cessary share in the phaenomena. 



The evolution of nitrogen from springs has been discussed by Origin of 

 Berzelius, Anglada, and others. '^''^ "'"^''' 



Berzelius II supposes it to arise from the decomposition of the ^^"' 

 organic matter which these waters contain, whilst Anglada *f[ 



* Vulkanischen Miner alquellen, p. 255. 



t On Valleys of Elevation, Edinburgh New Phil. Journal, October, 1830. 



I See my memoir on Thermal Springs already referred to. 



§ Jahresheiicht, vol. vii. p. 352. 



jl " Analyse des Eaux dc Carlsbad," Jnn. de Chini., vol.xxiii. 



if Me'moires pour servir, 8fc. 



