460 Royal Institute of France. 
with those of which the origin, either volcanic or non-volcanic, 
is incontestable, is to be ascribed to the circumstance of both 
being often composed of particles so mixed, and reduced into a 
paste of an appearance so homogeneous, that it is impossible to 
discern them with the eye, Chemistry cannot here come to 
the assistance of the senses, because it confounds all those par- 
ticles in its analysis, and only gives as a result the sum total of 
their primitive elements, in place of distinguishing those which 
belong to each of their species. 
M. Cordier, therefore, contrived a new mode of mechanical 
analysis, which consists in reducing in the first place into small 
bits, the mineral specimens the existence of which we may sus- 
pect in rocks which we wish to examine; 2dly, determining 
clearly the physical characters of those parcels, and their man- 
ner of acting when exposed to the blowpipe; 3dly, pulverizing 
the rocks submitted to examination ; and lastly, in washing and 
sifting the various particles detached by this pulverization, and 
submitting them to the same tests to which parcels of substances 
well known are subjected. 
This is, as may be seen, a kind of microscopical mineralogy, 
from which M. Cordier has derived great advantage. The 
pastes, known by the name of lavas, and historically stated as 
such, were easily detected by this new analysis: their particles 
were easily separated: they exhibited but a small number of 
combinations, in which sometimes feldspar prevailed, sometimes 
pyroxene, and in which they were alloyed in various proportions 
with the ore of iron denominated ¢itaniwm—with those three 
elements are mixed, but in a manner less general, amphibole, 
amphigene, mica, peridot, and oligistous iron. 
The basaltic pastes of an origin more or less contested were 
as easily divided into their constituent parts, and those parts 
were not found different. All those ancient or modern pastes, 
whether recognised as lava or not, are therefore, according to 
the author, microscopical granites, in which the uniformity of the 
intermixed texture is interrupted only by very small vacancies 
a little less rare in some lavas than in others, and which ap- 
peared to the naked eye to be homogeneous masses, in which 
are prevalent either the characters of the pyroxene or those of 
feldspar, and which cannot then be distinguished but by two 
sorts. 
A part of the scori@ whicheaccompany the stony lavas, and 
which are the first products of the coagulation of matters in 
fusion, are also composed of various grains, but finer, less re- 
gularly interwoven, and nevertheless of the same species with the 
masses which they cover; another part more changed by the 
action of fire approaches more the vitrified state: others, 
finally, 
