168 
TRANSACTIONS OF THE PLYMOUTH INSTITUTION. 
swept away to the westward of Torbay, is as certain as that these 
rocks are as steadily, if less quickly, wasted now. Nor are we 
without materials for rilling up part at least of the interval. 
The Miocene lake of Bovey Tracey, twelve square miles in area, 
is a mass of Dartmoor debris? brought down by the Teign and 
its tributaries ; and if the other rivers of the Moor then did a 
proportionate amount of work, we can gain some idea of the 
enormous quantity of matter removed from its face during that 
period alone — a mass equivalent at least to hundreds of feet in 
thickness over the whole of the central region. Nearer to us we 
have the scraping and scooping of the Glacial age. The evidence 
for this indeed is inferential rather than direct ; but I do not myself 
see how, apart from ice action, we are to account for some of the 
expanding hollows and filled-up lakelets along our river valleys, 
or for sundry of the deposits of clay and subangular stones which 
not only occupy bottom lands, but coat in so many places the slopes 
of the granite hills 1 and are frequently cut through in miniature 
ravines by the brawling little torrents of sudden and heavy 
rainfall — all indicating an amount of denudation of which the 
material left behind is a very inadequate gauge. 
And then we have the remains of old river gravels at high 
levels along the courses of various Dartmoor streams, with such 
allied proofs of former waste as we find in the pebble and sand 
and clay beds of the Hoe (distinctly of Dartmoor origin) ; in such 
isolated patches of granitic gravel — the poor remnants of wide 
sheets — as that of Petrockstow, twelve miles from the nearest 
point of the Moor ; and in the granite pebbles of the Haldon 
gravel, 800 feet above the sea — each and all themselves but 
denuded vestiges of the ancient demolition which gave them 
birth. 
9 Analyses of natural and artificial china clay give these results : 
Silica. Alumina. Potash. Water. 
Dartmoor Kaolin 47'20 38 20 2'0 1274 
Bovey Miocene Clay 49'60 37 '40 ... 11*20 
1 So with the granite boulders frequently carried forward a considerable 
distance over the slates. They are not only remarkable testimonies to the 
strength of the denuding forces, but of the existence of heights long planed 
away. In like manner the occurrence of non-granitic debris within the 
granite area recalls the days when the covering rocks stretched up the slopes 
of the Moorland region far beyond their present limits. The fragmental 
deposits of the Moor are full of interest. 
