436 On a Phenomenon 
still used these blocks for some particular purposes, as they 
are harder than the granite of the quarries. 
This is not the ‘only fact which I related in the same 
volume of my Travels, observed also with Mr. Davies Giddy, 
embracing all the phenomena above described; viz. The 
stratification of granite, ihe nature of the veins in St, Mi- 
chael’s Mount, and the dispersion of blocks of granite on 
the surface of the soils. There is a mount named T regon- 
ning Hill, about seven miles distant from Mr. Giddy’s s house, 
where he was so good as to carry mein his chaise. The 
account of our observations begins at p. 270. 
Tregonning Hill, in its highest part, is about six hun- 
dred feet above the ‘neighbouring valleys: at its foot, after 
having cleared the rubbish from the surface, have been 
found very regular strata of granite of the same kind as 
that of St. Columb: but the workmen told us, that when 
they followed them within the hill, they were found to be 
insulated masses buried in rubbish. In some of the exca- 
vations where similar masses had been entirely taken up, 
we saw nothing but rubbish in the place where they had 
lain. This phenomenon, of which I have given instances 
in my Travels, concerning masses of regular : sirata, both of 
schisius and ‘ime- stone, “buried in rubbish, is an evident 
proof, that the valleys around have been produced by the 
subsidence of part of the strata, at the same time that 
the parts remaining outwards were broken and inclined in 
various mauners 5 which is one of the greatest geological 
facts. 
After these observations, we ascended the hill towards a 
signal-post, which is on the highest part. The observa- 
tions we made on this hill begin at p. 273. We saw on 
the turf, more or Jess covered with grass, a great number 
of masses of the same granite as Mount St. Michael, with 
all the veins which bad been the object of our observations 
yn the island, but with more variety. These veins. were 
even observable in such small fragments as I could carry 
with me.—One of these specimens, the two outsides of 
which are of the same granife as that of the mount, has a 
vein of pseudo-granile one inch and half in thickness, with 
its capel of quarts as in the mount; the quarts is grayish 
al its contact with the pseudo-granite: there is no mica in 
the latter, though there is mca in the granite on the sides ; 
a difference of which Mr. Playfair had not taken notice, 
since he asserted “ that itas wndistinguishable {rom the mass 
of the hill.”,—Another mass which has also granite on i 
sides, 
