238 Natural History of Volcanos and Earthquakes. 



common salt.* In my frequent excursions in the vicinity of the 

 Laacher iSee and in the Eifel, I have never found any efflores- 

 cence of salt either on the undisturbed or fresh broken lavas, and 

 other products of the extinct craters in those districts. On the 

 uncovered walls of trass, in the Brohl valley, efflorescences are, 

 indeed, to be found, but they contain chlorides only as very sub- 

 ordinate ingredients.! The lixiv^iation of trass, basalt, and other 

 volcanic rocks, also gives but a trace of common salt.J That 

 muriatic acid must have played a very insignificant part in the 

 eruptions of these ancient volcanos, seems to be proved by the 

 mineral springs which rise in their vicinity ; for common salt is 

 one of their least considerable components, indeed they frequently 

 contain mere traces of it. This is the result of more than forty 

 analyses of mineral springs in those regions, which I have under- 

 taken during these last iew years. But these waters would ex- 

 tract the chlorides from the volcanic masses through which they 

 flow, if they existed in any considerable quantities in them, and 

 would return impregnated with them to the surface. 



From all this we do not seem to be justified in considering the 

 chlorides as the chief agents in volcanic phenomena, although it 

 cannot be denied that they may, in some instances, co-operate in 

 their production.^ It has even been supposed that the beds of 



* Loco cit. p. 181. t Die vulkanischen Mineralquellen, ifcc. p. 243. 



% Idem, p. 246 and 247. 



§ Many volcanos have produced considerable quantities of common salt, as, for 

 instance, Vesuvius, Hecla, &c. Also sal-ammoniac is found among the volcanic 

 sublimations of Vesuvius and Etna, and almost exclusively in some volcanos of 

 the interior o? Asia. Vauquelin found in a porous rock, constituting a considera- 

 ble part of the Puij de Sarcouy. in the chain of the Puy de Ddme, 0.055 of muriatic 

 acid, which is worthy of remark in connection with the frequent occurrence of 

 iron-glance in that neighborhood. (Ann. des Mines, vi, p 98.) There are fel- 

 spar crystals in the trachyte, colored sulphur-yellow by muriatic acid vapors of a 

 former time. Common salt also forms the chief ingredient in the thermal springs 

 of Si. JYectaire, in the department Puy de Dome. In the mineral springs of Mont 

 d^Or, Vichy, Chaudes-Jiigues, Vals, &c., on the contrary, it is in very small quan- 

 tities. In the lavas of Etna 0.01 of muriatic acid has been found. In basalt, Ken- 

 nedy found 0.01 ; Klaproth 0001 ; and I, 0.00085 of muriatic acid. I also found 

 that acid in a steatitic substance in the trachyte conglomerate of the Siehengebirge. 

 See " Die vulcanischen Mineralquellen," p 277. But this occurrence of muriatic 

 acid, which may, perhaps, be found in many other volcanic productions, is far too 

 inconsiderable for us to ascribe to it any great part in the production of volcanic 

 phenomena. Proust tells us that, according to Garicas Fernandez, the celebrated 

 salt mines at Poza, near Burgos, in Old Castile, are situated in the centre of a cra- 

 ter, in which the latter collected various volcanic products. Journ. de Phys. vol. 

 Iv, p. 457. 



