1816.) Royal Institute of France. - ~~ 811 
_ The basaltic pastes of a more or less disputed origin were divided 
with equal ease into their constituent parts, and these parts were 
pot found different. All these ancient or modern pastes, whether 
considered as lavas or not, are then, according to the author, 
microscopic granites, in which the uniformity of the mixed tissue 
is only interrupted by smal] voids, somewhat more common in cer- 
tain lavas than in others, and which appear to the naked eye homo- 
geneous masses, in which predominate either the characters of 
augite or of felspar, and which therefore can only be distinguished 
into two kinds. 
A part of the scoria which accompany the stony lavas, and which 
are the first products of the coagulation of the matters in fusion, 
are composed likewise of different grains, but finer, less regularly 
mixed, and yet of the same species as the masses which they cover, 
Another portion, more altered by the action of fire, approaches 
more toa vitrified state. Others are completely in that state; but 
still sufficient traces of their origin remain to enable us to recognise 
it. They always belong to one of the two principal orders of com- 
bination observed among stony lavas. 
M. Cordier endeavours to explain, by the different state of the 
scoria, a phenomenon which has struck several travellers, that 
some currents of lava remain always sterile, while others are speedily 
covered with the finest vegetation. It is because the former, being 
more vitrified than the latter, are less easily decomposed. 
The author examines likewise the obsidians, or volcanic glass 5 
and comparing all the shades of their greater or less vitrification, he 
always finds traces of augite or felspar the principles which predo- 
minate in the two orders of lavas; and the obsidians fused into a- 
black glass have shown perfect transitions to the most dense basalt. 
In a word, obsidian, scori#, lavas, basalts, do not differ in compo- 
sition, but only in the peculiarities of their texture. Even in vol- 
canic sand and ashes we may find, by washing, the same materials 
whose aggregation forms the neighbouring lavas. M. Cordier has 
followed these materials in the different substances after they have 
been altered by time, and has disengaged from them the new sub- 
stances which have made their appearance in them, or which have 
filtered into their vacuities. He has not neglected the examination 
of any modification of these volcanic products, whether true or dis- 
puted, and he has every where found these general laws to hold; 
but when we pass to the ancient trap rocks, to which it has been 
attempted to refer the basalts, none of these marked characters can 
be perceived which establish such undoubted relations between 
lavas and basalts. ) 
The mass of these ancient rocks has no apparent voids; we 
scarcely perceive grains in them, and they do sot differ from each 
other in colour. They cannot be divided into separate parts ; no 
mechanical analysis can be made of them. Consequently if a part 
of these rocks is composed of heterogeneous materials, it is impos- 
