^4 SIXTH REPORT — 1836. 



bonic acid ; but when we perceive the large proportion of soda 

 indicated by the analysis, it seems quite as probable that these 

 earths existed in the water as muriates or sulphates, and that 

 they were precipitated in the state of carbonates by the car- 

 bonate of soda, on concentrating the solution. 



The same explanation may be extended to the cases of Schinz- 

 nach, Weissenburg, Pfeffers, and Loueche amongst the thermal, 

 and to Gurnigel and Engistein amongst the cold carbonated 

 springs ; whilst at Fideris, Tarasp, Luxemburg (in Thurgau), 

 and others, carbonate of soda is stated as abundant. 



But the greatest difficulty, as appears to me, is presented by 

 the thermal waters of the Pyrenees, which are for the most part 

 richly impregnated with soda, and yet are derived exclusively 

 from granitic rocks, or others equally destitute of mineral alkali. 

 Should future observations, directed expressly to these parti- 

 cular points, substantiate the fact of the entire absence of potass 

 from these springs, and that of the scanty presence of soda in 

 the rocks with which they are connected, I apprehend the hypo- 

 thesis of Bischof, plausible as it may seem, and well as it may 

 suit the case of "volcanic mineral waters," must be al)andoned, 

 and the same theory be extended to the carbonate of soda, which 

 we have already applied, to the boracic acid present in the La- 

 goni of Tuscany, and to the common salt exhaled from the cra- 

 ters of volcanos. 



There seems at least no absurdity in supposing, that if, as I 

 "ry pvopo- shall afterwards attempt to show, thermal springs owe their 

 *<=^- temperature to steam and gases given out by volcanic processes 



carried on underneath, the former may carry with it, not only 

 boracic acid, but also soda, which, in its passage upwards, inight 

 enter into combination with the muriatic, the sulphuric, the 

 carbonic, or any other acid that was present. 

 Origin of We need not however resort to any such hypothesis in order 



the Carbo- j-q accouut for the occasional presence of carbonate of soda in 

 "'"c^ena^n*^^ secondary strata. In salt lakes which become nearly dry in 

 leco'i'clary summer, a portion of natron will often result, either from the de- 

 rocks, composition of the muriate of soda by calcareous matter, in con- 

 sequence, as is supposed, of the operation of the law of Berthol- 

 let with respect to the influence of the mass, or, as is more pro- 

 bable, from the conversion of sulphate of soda l)y organic nuit- 

 ter into sulphuret, and the decomposition of the latter by the 

 earthy carbonate. To one or other of these causes we ascribe 

 the natron of Hungary, and perhaps that existing in certain 

 mineral waters of Bavaria, said to be remote from volcanic or 

 trappean rocks. 

 Soda with- In the cases hitherto mentioned, the alkali has been supposed 



New The- 



