310 Proceedings of Philosophical Societies. [ApRit, 
ROYAL INSTITUTE OF FRANCE. 
Account of the Labours of the Class of Mathematical and Physicat 
Sciences of the Royal Institute of France during the Year 1815. 
Puysicat DerarrmEnr.—By M. le Chevalier Cuvier, Perpetual 
Secretary. 
(Continued from p. 233.) 
MINERALOGY AND GroLoey. 
Among the questions which philosophers, occupied with the 
theory of the earth, usually agitate, there are few more difficult, or 
which have occasioned longer or more obstinate disputes than that 
on the origin of basalt and wacke, rocks which some consider as 
products of ancient volcanoes, while others view them as deposites 
from the general liquid in which the common rocks were formed, 
and as analogous to primitive trap. 
M. Cordier, Divisionary Inspector of Mines, and Corresponding 
Member of. the Class, having turned his attention to this problem, 
has contrived methods of resolving it, which are entirely new. 
His first reflections enabled him to perceive that the greatest diffi- 
culty to compare matters of a disputed nature with those whose 
origin, whether volcanic or non-volcanic, is incontestable, depends 
upon this, that both are often composed of particles so mixed and 
reduced into a paste apparently so homogeneous, that itis impos- 
sible for the eye to distinguish them. Here chemistry cannot come 
to the aid of the senses, because it confounds all these particles in 
its analyses, and only gives as a result the list of their primitive 
elements, instead of distinguishing those which belong to each 
species. 
M. Cordier, therefore, contrived a new mode of mechanical 
analysis, which consists in reducing to parcels the mineral species, 
the existence of which we have reason to suspect in the rocks which 
we wish to examine; to determine correctly the physical characters 
of these parcels, and their action under the blow-pipe; then to 
pulverise the rocks which we are examining, to separate by fanning 
or washing the different sorts of particles which this pulverisation. 
has separated from each other, and to subject them to the same ex- 
periments as the different parcels of well known substances have 
undergone. , 
This is, as we see, a kind of microscopical mineralogy, of which 
M. Cordier has made an excellent use. The stony pastes, known 
to be lavas from historical proof, were readily subjected to this 
analysis. Their particles very easily separated. They presented 
but very few combinations, in which sometimes felspar predomi- 
nated, sometimes augite, and in which titaniated iron was mixed in 
various proportions, With these three constant elements were 
mixed, but in a less general manner, hornblende, leucite, mica, 
olivine, and specular iron ore, 
