34 Prof. Bischof on the Naiiiral Historij of 



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, al- 

 though it cannot be denied that tliey may, in some instances, 

 co-operate in their production.* It has even been supposed 

 that the beds of rock-salt are of volcanic origin. But this 

 proves nothing more than that rock-salt may have been raised 

 from the interior of the earth by volcanic power, and that the 

 beds of salt are a consequence of volcanic action, but not con- 

 versely, that chlorides and the disengagement of muriatic acid 

 are the cause of that phenomenon. 



Now, since neither any process of oxidation, nor processes in 

 which chlorides take an active part, are capable of affording a 

 satisfactory explanation of volcanic phenomena, we can scarcely 

 conceive any other powerful chemical process, which could alone 

 give rise to them. We may, therefore, look upon the hypo- 

 thesis which seeks the cause of volcanic phenomena in intense 

 chemical action as untenable. 



* Many volcanos have produced considerable quantities of common salt, 

 as, for instance, Vemt'm?, Hecki, &c. Also sal-ammoniac is found among the 

 volcanic sublimations of Vesutius and Etna, and almost exclusively in some 

 volcanos of the interior of Asia. Yauquelin found in a porous rock, con- 

 stituting a considerable part of the Puy de Sarcouy, in the chain of the Fny 

 de Dome, 0.055 of muriatic acid, which is worthy of remark in connection with 

 the freqvient occurrence of iron-glance in that neighbourhood. (Ann.des JIus. 

 vi. p. 98.) There are felspar crystals in the trachyte, coloured sulphui- 

 yellow by muriatic acid vapours of a former time. Common salt also 

 forms the chief ingredient in the thermal springs of St Nectaire, in the de- 

 partment Pay de Dome. In the mineral springs of Mont d'Or, Vichy, Chaudcs- 

 Aignes, Vah, &c. on the contrary, it is in very small quantities. In tlie 

 lavas of Etna 0.01 of muriatic acid has been found. In basalt, Kennedy found 

 0.01 ; Klaproth 0.0001 ; and I, 0-00085 of muriatic acid. I also found tliat 

 acid in a steatitic substance in the trachyte-conglomerate of the Siehenyebinje. 

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

 juuriatic acid, which may, perhaps, be found in many other volcanic 

 productions, is far too inconsiderable for us to ascribe to it any great part 

 jn the production of volcanic phenomena. Proust tells us that, according 

 to Garicas Fernandez, the celebrated salt-mines at Poza, near Burgos, in Old 

 (kigtHe, are situated in the centre of a crater, in which the latter collected 

 various volcanic products. Joura. de Phys. vol. Iv. p. 457. 



