150 TRANSACTIONS OF THE PLYMOUTH INSTITUTION. 
granite is the primary rock of the world — once firmly held — is 
long quite out of date, since it has been recognised that there are 
granites of differing geological ages ; and instead of one hypothesis 
for the origin of granite, there are now four — (1) The original 
primary idea, repeated only by the uninformed; (2) The generally 
received view that granite is of igneous origin ; (3) The sugges- 
tion that it is really an altered stratified rock ; (4) The com- 
promise theory that as there are granites of different ages, so 
there may be granites of different origins — some igneous and 
some me tarn orphic. 
With the first and fourth of these we have nought to do. The 
one is dead; and as for the other, we are only concerned with the 
granite of Dartmoor and its continuation west, and what may be 
proved touching them. 
The difference between the second and third hypotheses is not 
absolute. We are not really troubled about the prior condition of 
the material which now forms the Dartmoor granite. It may have 
been igneous from the beginning (and all rocks were originally 
igneous), or it may have been a sedimentary rock, subjected to 
destructive action and reconstitution. At the same time it should 
be mentioned that in 1875 the late Mr. J. A. Phillips clearly 
proved that granite and elvan could not have been formed out of 
killas, which is deficient in silica, and contains more soda than 
potash, while granite and elvan are potassic. 1 If therefore our 
granites and elvans are metamorphic, special forms of sedimentary 
rock must have been provided, occupying exactly the same areas, 
which have left no trace behind ! 
Our business, however, is not with original character, but with 
agency. And here again the dispute is in part one of terms. 
Most, if not all, geologists are agreed that what is now granite has 
been in a fluid or semi-fluid, or at least pasty condition, produced 
in some way by heat. The controversy, so far as we have to do 
with it, is narrowed to one point — whether the heat was dry or 
wet, thermal simply, or hydrothermal — whether, in plain English, 
our granite was smelted or stewed. 
And the advocates of the rival views also agree that, however the 
fluid state was originally produced, the consolidation of the granite 
must have taken place under considerable pressure. 
Liquid and gaseous inclusions frequently occur in cavities in the 
1 Quar. Jour. Geol. Soc. xxxi. 338. 
