of St. Michael’s Mount in Cornwall. 433 
Continuing our walk round the island, we ascended to 
a certain height the part of the rock on which lies the way 
to the castle, in order to observe the eastern coast of the 
bay, whence this island is but at a little distance. Most 
of the clifts on this side are the section of a very thick 
loose soil; but beneath their feet are seen masses of 
schistus in great disorder ; and all the bed of the sea along 
the clifts presents /edges of the schistose strata desc ending, 
under the water, with an inclination towards the west.” 
This appeuratice: Reems, at first, to be equally explained 
by the system of the subsidence of a part of the bed of the 
sea, or the lifting up of the part of it which is become our 
continent. This last being Mr. Playfair’s system, he ap- 
plied it to the phenomena of St. Michael’s Island. But 
I opposed to him, that the operation of lifting up could 
be only effected by the production of an immense quantity 
of elastic fluids under strata already broken ; and that these 
fluids making their escape through the crevices, the mass 
then, unsupported, would have fallen down again : an argu~ 
ment to which he has not answered, and the state of the 
bed of the sea in Mount’s Bay shows directly that this 
would have been the effect, 
Another object of my controversy with Mr. Playfair was 
on the nature of granite. Ju the Huttonian system, gra- 
mite is supposed to have been a product of fusion by heat 
under those of the mineral substance, which they acknow- 
ledge to have been formed in strata; and. Mr, Playfair 
thought to have found a proof on that opinion in the veins 
of St. Michael’s Mount, supposing them, as it has been 
seen above, to be real granite. 
The system which I have opposed to that opinion is 
mentioned by Mr. Allan in these words: ** Those (he 
says) who were inclined to consider this rock as an or iginal 
deposite, have accounted for its formation in different ways.’ 
I think that, as Mr. Allan mentions me for a part of the 
subject, he ought to have expressed not only the way that 
I have explained the production of granite, but the proof 
which he might have found in my works. A fact’ w hich 
I adduced to Mr. Playfair, to prove that granife is an ori- 
inal deposite on the bed of the former sea, 1s, that we find it 
in strata as regular as those of all the other mineral substances, 
This { first stated in a work published in London in.) 809, 
undef the title of Elementary Treatise on Geology, in which 
I demonstraied that granite was the first substance pro- 
duced by chemical precipitation on the bed of the former sea, 
where it was covered by a succession of other strata; and 
Vol. 42. No, 188, Dec, 1813. Ee tha: 
