META]y;OKPHISM. 
47 
of mica-scliist_, some of wliich. show a ripple mark^ while all 
exhibit more or less of mechanical origin_, have originated in 
deposits made in water. Even gneiss_, though often different 
from schists and resembling granite^ and sometimes passing 
into that rock_, must be referred to the same agency. 
But when we come to granite^ it may be supposed that the 
case is different. Including under that general name all the 
varieties of rock in which crystals of quartz^ of potash or soda 
felspar of white and black mica, of hornblende_, and of other 
minerals^ are embedded in a paste of quartz or felspar^ and 
looking at its position (generally underlying or thrust up 
through other rocks) ^ we seem to have reached the original 
rock^ and first appearances would suggest that this must have 
been in a state of igneous fusion. But more minute and care- 
ful observation satisfies the geologist that granite^ like other 
more familiar rocks_, may be but a modification of the rest ; 
that as it is sometimes inter- stratified with slates and schists^ 
it musri in all probability^ have a similar origin ; and that all 
the extreme peculiarities of structure it presents may be only 
a still further carrying out of the great principle of metamor- 
phism^ so that granite is a metamorphosed rock in the strictest 
sense of the term. 
On examining the condition of the minerals of which granite 
is composed^ it is impossible not to arrive at a similar conclu- 
sion. It consists, to a large extent, of quartz. Now, quartz may 
result either from igneous fusion or aqueous solution. In the 
former case, however, as determined by experiment, its specific 
gravity is 2*2 only, while in the latter it is 2*6. The specific 
gravity of quartz in granite is 2*6, as is well known. Again, a 
particular kind of mica, containing no less than 4 per cent, of 
water, forms an important part of some varieties of granite. 
Certain minerals, which swell and alter their properties on 
exposure to a much lower heat than is needed to melt granite, 
abound in some varieties of the rock. And, lastly, there are 
several distinct minerals forming granite which would cool in 
a certain order if they had all been fused together, but the 
order in which they have been formed as crystals does not 
agree with this sequence. « 
There are other reasons why it is impossible that granite 
can have existed in a fused state. The quartz of which it is 
made up has certainly crystallized from an aqueous solution, for 
it not only contains water in its composition, but it is often 
full of minute cavities filled with water. These cavities are, 
no doubt, small, but they are marvellously numerous. In some 
specimens of quartz they are not two of inch apart. The}^ 
occupy five per cent, of the volume of the mineral, and as much 
as one-half per cent, of the weight of the quartz is got rid of 
