and the Nature of the Liquidity of Lavas. 197 
proportionate dimensions of the mass would be equally varied so 
as to produce a section something like E, F, G, H (fig. 5); in 
Fig. 5. 
fact, a rock which, if no further change occurred in it except 
consolidation in place, would have all the characteristics of 
gneiss. The same movement, if still further continued, might, 
it appeared to me, be expected to disintegrate the angular cry- 
stals of felspar altogether, so as to cause them to disappear, 
perhaps to force their elementary molecules to melt into the in- 
tensely heated silicate, to which they would impart their alkalies. 
And the resulting rock, supposing the lamin of the mica- 
crystals to slide readily past each other, when lubricated by the 
silicate, and not therefore to be so far disintegrated as those of 
felspar (as from their peculiar form might be expected), would put 
on a lamellar structure, and very much resemble mica-schist,— 
especially since the great flexibility of the mica would render its 
laminz extremely liable to yield to the irregularities of pressure 
pervading the mass in a variety of directions, and consequently 
to take such wavings and contortions as are often exemplified in 
that rock. Whoever will examine the tortuous way in which 
the plates of mica envelope and bend round nodules of half- 
melted quartz or crystals of garnet in mica-schist, will be con- 
vinced, I think, that the whole mass has been subjected to great 
internal movement and consequent friction in the direction of 
the layers of mica, while under intense pressure, and in a com- 
paratively softened state, the mica being lubricated, as it were, 
by a vehicle of liquid or gelatinous quartz. Whatever fissures or 
cracks were formed during this movement in the semi-solid rock, 
or subsequently, so long as the silicate remained unconsolidated, 
would be necessarily filled by it, and ultimately appear in the 
shape of the quartz-veins so frequent in this class of rocks. 
Under this supposition, gneiss and mica-schist would bear the 
same relation to granite as the ribboned trachytes and schistose 
lavas (clinkstone) to ordinary crystallized or granular trachyte ; 
and the quartz-rocks associated with granite represent the quartz- 
ose trachytes of Hungary, Fonza, and the Andes. 
These views, developed by me in 1825, I cannot but think 
