637 



stantly anhydrous) are the effect of overflowings 

 across the crevices which have traversed the 

 oxidated crust of our planet, and penetrated to 

 the seat of volcanic action. The enormous 

 masses of muriate of soda (chlorure de sodium) 

 recently thrown up by Vesuvius *, the small 

 veins of that salt which I have often seen tra- 

 verse the most recent lithoide lavas, and of 

 which the origin (by sublimation) appears 

 similar to that of oligist iron deposited in the 

 same vents the shelves of gem-salt and sali- 

 ferous clay of the trachytic soil in the plains 

 of Peru, and around the volcano of the Andes 

 of Quito J, are well worthy the attention of 

 geologists who would discuss the origin of for- 

 mations. In the sketch which I here trace, 

 I confine myself to the simple enumeration of 

 the phenomena of position, indicating at the 

 same time some theoretic views by which ob- 

 servers placed in more advantageous circum- 

 stances than I was myself, may direct their 

 researches. 



* Laugier and Gailla, in the Annates du Mus., 5e annee, 

 No. 12, p. 435. The ejected masses in 1822, were so con- 

 siderable, that the inhabitants of some villages round Vesu- 

 vius, collected them for their domestic use. 



+ Gay-Lussac, on the action of volcanos, in the Ann. de 

 chimie, Vol. xxii, p. 418. 



t See my geogn. Essay, p, 251. 



