in his Paper on a saline Substance from Mount Vesuvius. 133 
‘ome out successively /avas and showers of cinders, which b 
degrees produce an accumulation in the form of a cone ; wid 
the materials of such mounts are as distinct from the original 
strata, as iron is from wood. 
The author has no real knowledge of the various ejections of | 
Mount Vesuvius, since he derives his hypothesis from the speci- 
men of a saline substance sent to him from Naples. But to 
conclude a system on that spec?men, is the same as to decide the 
nature of all the minerad strata of an unknown country, from a 
JSragment of stone. If he had known my geological work above 
mentioned, Histoire de la Terre et de 1’ Humme, he would have 
found in it, from the observations of my brother, such an exact 
description of all the phenomena of volcanoes, as must have 
superseded in his mind the erroneous information which he ap- 
pears to have received from Naples. 
Nobody, to my knowledge, has observed the various voleani¢ 
phenomena more thoroughly than my brother, not only of Ve- 
suvius, but of Etna, and of the volcanic islands of Lipari, near 
Sicily. He has seen actual eruptions of Vesuvius, and followed 
the steps of new davas flowing over old lavas. This progress 
continues as long as the new /ava retains a sufficient heat to 
maintain its softness; but at a greater or smaller distance, 
though still red hot, it hardens and breaks; then the broken 
pieces, still propelled by the soft dava, rise in heaps at the ex- 
tremity, and tumbling over one another, they produce a particu- 
lar noise heard at a considerable distance. Such are the real 
characters of davas, unknown to the author, who has never had 
the opportunity of observing them himself. 
My brother has been no less attentive to the saline and sul- 
plureous substances observed on the sides of Vesuvius. The 
author says he was informed by a letter, that the saline substance of 
which he had received a specimen, had flowed liquid from a small 
aperture in the cone of Vesuvius. 1 think he might have judged 
himself, that this was impossible. How could so small a quan- 
tity of matter, suspposed to be in igneous fusion, preserve the 
heat that is supposed to make it liquid, while passing through a 
great thickness of old lavas, long reduced to the temperature of 
the air? This supposition, therefore, is absolutely improbable. 
My brother, who has carefully observed those substances that 
appear on the surface of the old davas towards the top of 
Vesyvius, and has detached fragments of them preserved in our 
collection, has invariably found that they had been, and con- 
tinued to be, produced in crevices which emit fumes: thus show- 
ing that these substances are a sort of swblimation which accu- 
mulates against the sides of the crevices, without any appearance 
of their having been ever in a liquid state, 
: 7m 13 With 
