DISCUSSION ON DARTMOOR. 
93 
DISCUSSION ON DAKTMOOR 
(continued). 
W. GAGE TWEEDY, B.A., AND R. N. WORTH, F.G.S. 
(15th March, 1888.) 
Mr. Worth dwelt on the geology of Dartmoor. He described in 
succession the Archaean, the Silurian, and the Devonian seas, and 
next the Carboniferous. Dartmoor did not exist until all these 
eras had passed, because the rocks of which the moor was com- 
posed rose up through the Carboniferous. At the time Dartmoor 
originated there was a district composed of rocks of the periods 
mentioned, and in the centre there was a tremendous upheaval, 
the moor being now nothing more or less than the stump of a 
very considerable volcano which once reared itself high in the 
air. "What had taken place since had been a steady reduction in 
the size and character of that mountain, which was going on 
perpetually, until its elevation was now half a mile ; when at its 
highest it must have been at least two and a-half miles. The 
change in the heart of the rocks was best shown by the production 
of china clay ; the great central change that had taken place in the 
mass of the granite of Dartmoor. Other changes arose from the 
upthrust and outburst of younger rocks, and the formation of 
mineral veins. Eelative to visible changes, Mr. Worth remarked 
that those who knew the moor from year to year found points 
where changes were taking place — the rocks were weathering. 
The surface of the moor was covered in some places by loose 
stones, which were commonly associated with glacial boulders. 
But, unlike these, the Dartmoor blocks had not travelled very 
far, for, as a rule, they could find the parent rock not very far 
off. These "clitters," as they were called, were, however, very 
gradually going down hill. Though it was now deficient in them, 
Devonshire had at one time many lakes. The site of the Head 
Weir was the bed of an old lake, formed by the Meavy, the 
