94 
TRANSACTIONS OF THE PLYMOUTH INSTITUTION. 
barrier of which was just below Sheepstor Bridge, where the 
rocks rose very high, and formed a kind of gorge. The processes 
that had resulted in degrading the volcano of Dartmoor from its 
original size to a stump would continue to go on until Dartmoor 
was brought down to the level of the sea. 
Mr. Tweedy remarked that the idea that Dartmoor once towered 
up above this country as a mountain 10,000 feet high was some- 
thing startling. But if they considered the enormous deposits in 
all the estuaries around Devonshire they saw that something of 
that kind must have occurred to account for it. On the moor 
they were constantly coming across large masses of granite cleft 
in two ; but if they examined them they found that there had 
been no real separation. The granite was lying on its original 
bed, and the separation was simply due to the slow crumbling 
away of the stone itself. In one instance this had apparently 
amounted to at least a foot in one great block, while if they 
looked at any of the crosses set up on the moor they saw the 
same thing. Hence it was that so few inscriptions could be found 
on the stones, and even those cut for Mr. Bray by a professional 
stonecutter were so crumbling and obliterated that it was impossible 
to make them out. Mr. Tweedy gave particulars of the number 
of mines formerly worked on Dartmoor. Was there any way, 
he asked, of accounting for the failure of mining except on the 
supposition that the tin found on the surface was the residue of 
the veins that were contained in the great pile two miles high 
that once existed on the spot 
