President's Address. 
7 
tinued heat on metals and minerals, says — "The crystalli- 
zation of the primary rocks was supposed by the early 
Plutonic theorists to be due to slow cooling ; but this 
principle alone does not satisfy the phenomena. The crys- 
talline structure of granite is seen, for example, in Glen 
Tilt, at Shap Fell and elsewhere, to be equally uniform in 
its partial irruptions into the superior strata, as where it 
appears to be the foundation-stone of the earth's crust it 
has crystallized in its accustomed manner, where it has 
penetrated fissures of the upper beds in plates as thin as the 
leaves of a book, and threads as fine as a hair ; and even 
where it is involved in the invaded stratum^ so that no junc- 
tion with any vein can be observed. How could it have 
been thus injected in a state of fusion unless of the most 
liquid kind ? and how could the heat of such liquidity, in a 
material of which the fusing point is so high, be otherwise 
than rapidly cooled down ?" Yet this difficulty does not 
prevent the reverend gentleman from still believing that 
the granite was of igneous origin, and persists in his belief 
in the face of the fact, that " the quartz which forms so 
large a constituent of granite has always the specific 
gravity of crystalline silica, which exceeds that of any other 
species of silica ; and Deville and others have shown that 
fusion lowers this specific gravity to a constant amount, and 
that fused silica does not recover its density in cooling. 
Crystalline granite, as Delesse has shown, passes by fusion 
from the density of 2-62 to that of 2-32, and Egyptian 
porphyry from 2-76 to 248.'' 
The Plutonists, in their anxiety to maintain the old doc- 
trine of internal heat, have not, in my opinion, improved 
their position by discovering that the ramified granite of 
Glen Tilt and Shap Fell is similarly crystallised with the 
rest of the rock, but only finer grained ; nor has the ex- 
periment of Mr Marshall, who fused a large mass of granite, 
and having slowly cooled it, failed to obtain crystals, aided 
their hypothesis. 
If the experiments of Hall were correct, and the specu- 
lations of Hutton true, we ought to find, wherever the gra- 
nites are intruded, metamorphic changes due to heat made 
