312 Proceedings of Philosophicai Societies. [Apriz, 
sible to determine the mineral species to which these materials 
belong. 
Their chemical analysis is likewise different, particularly because 
they contain no titaniated iron. 
Hence the pretended analogy between the traps and the basalts is 
not confirmed by a rigorous examination. 
As to the origin of the lavas, and the causes of their fusion, M 
Cordier does not venture to conjecture ; but considering their mass 
as coagulated by an instantaneous crystallization, he easily resolves 
the problem so long disputed, whether the crystals in lavas have 
been carried quite formed from the bowels of the earth, and enve- 
loped in them, or have been afterwards formed in their cavities, or 
have crystallized at the same instant that the rest of the mass con- 
solidated. It is easy to see that he adopts the last of these alterna- 
tives. | 
He terminates this great and fine undertaking by a methodical 
enumeration of the basalts, and the products of volcanoes, arranged 
according to their materials of aggregation, and under the two pre- 
dominating principles, felspar and augite. 
‘This nature so mysterious of volcanoes, these immense chimneys 
of heat, under circumstances quite different from these which sup- 
port fires at the surface of the earth, will long constitute one of the 
great objects of the curiosity of philosophers, and will excite their 
efforts as long as there remain any hopes of success. A young 
mineralogist, both.zealous and well-informed, M. Mesnard de la 
Groye (of Angers), having had an opportunity in 1812 and 1813 to 
observe several of the phenomena of Vesuvius, has drawn up a 
journal of them, remarkable for its exactness, and mixed with 
many original ideas and conjectures. 
Since the enormous diminution which the cone of the voleano 
underwent in 1794, when it sank more than 400 feet, all the erup- 
tions have taken place from the summit, which seems to have pre~ 
vented them from being so abundant and destructive as those which 
proceeded from the sides. The bottom of the crater has risen, and 
it is not impossible but it is filling up. Hence M. de la Groye 
draws as a conclusion that we must not always refuse to allow a 
mountain to be volcanic because it has no crater. 
The flow of lavas is the less abundant the greater the quantity of 
scorie and lapille thrown out of the volcano during an eruption. 
The whole cone is covered with these little stones, which are soon 
altered by the acid vapours, and assume those lively and variegated 
colours which give them at a distance the appearance of turf in 
blossom, and which have Jed naturalists into the opinion that the 
crater is filled with sulphur. This is so far from being true, that 
it is seldom we even perceive sulphureous vapours. On the con- 
trary, continued exhalations of muriatic acid are perceptible, and 
concretions of common salt are every where to be seen. 
M. Mesnard de la Groye from this divides volcanoes into two 
