and on the Origin of Granites. 37 
The numerous pseudomorphous felspars in the forms of anal- 
cime and Laumonite, described by Scacchi, Haidinger, Bischoff, 
and Rammelsberg, prove moreover that this mineral is easily 
formed in nature in the humid way. 
Mica can also be produced in both ways. The pseudomor- 
phous micas, in the forms of scapolite, felspar, and Andalusite, 
show the possibility of its formation under the influence of water. 
On the other hand, its presence in the lava of Vesuvius proves 
that it can also be formed inthe igneous way. But there seems 
to be an essential difference in the composition of mica, corre- 
sponding to these two opposite origins. 
Most of the micas, and particularly that of granite, contain 
small quantities of water and fluorine which are dissipated by 
calcination, so that the crystals become opake and lose their 
brightness. On the contrary this does not occur with the vol- 
canic micas, which contain neither water nor fluorine. This 
observation seems to establish the fact that the mica of granites 
must have been formed under the influence of water, and not of 
heat. 
But it is the examination of the quartzose elements which 
especially forces us to reject the hypothesis of the igneous origin 
of granite. It is recognized that quartz in granite generally 
moulds itself on crystals of felspar, and consequently has crystal- 
lized last of all, which fact is explicable on the hypothesis of a 
previous fusion. The attempt has been made to reply to this 
objection, by supposing that fused quartz might remain liquid 
at a temperature inferior to its point of fusion ; hence the theory 
of surfusion of M. Fournet. But, as M. Durocher remarked, 
the phenomena of surfusion are manifested only between very 
narrow limits of temperature, whilst it must here be admitted 
that the quartz had preserved its liquidity at least a thousand 
degrees below its point of fusion, which appears inadmissible. 
The quartz of veins often contain water or other volatile 
liquids, hydrated oxide of iron, carbonate of iron, and other 
minerals decomposable by heat, which facts, as M. de Sénarmont 
justly remarked, evidently prove its aqueous origin. With re- 
spect to the quartz of granites, it is often found in the form of 
smoky quartz, its colour arising from a volatile or combustible sub- 
stance, probably carbonaceous, which is expelled by calcination. 
It is impossible to explain the separation, in a fusible mass, of a 
very basic silicate, such as mica, from free silicic acid in the form of 
quartz, which, at an elevated temperature, plays the part of an 
energetic acid. Their formation in the humid way implies, on 
the contrary, nothing contradictory; for we know that at a low 
temperature silica scarcely plays the part of an acid, carbonic 
acid and even water surpassing it in energy in this respect. 
