158 TRANSACTIONS OF THE PLYMOUTH INSTITUTION. 
buttress of Archaean rock in the Channel, now represented by the 
Eddystone Keef, against which the Devonians were driven, and 
which, by its resistance, increased the plication. Where the rocks 
were freer to move the folds are less pronounced ; but similar 
effects are visible at many points round the Moor, where they 
have not been obscured by complicated earth movements or 
subsequent disturbance. 
If the stratified rocks between Dartmoor and the Channel are 
largely in excess of those that originally filled that space, whence 
have they come if not from part of the Dartmoor area ? And if 
the Dartmoor area, here and elsewhere, was cleared by the 
eruption of the granite of so much of its pre-granitic strata, is 
it not inevitable that the molten mass must have issued to the 
light as a volcano ? 
It is possible that to some of my hearers this may seem too 
large a draft on the powers of Nature; but in the most recent 
conclusions of the Geological Survey on Highland Geology I 
find the following passage : 
" By means of powerful thrusts the Silurian strata were piled 
on each other, and huge slices of the old Archaean platform, with 
the Cambrian and Silurian strata resting on it, were driven west- 
wards for miles." 
We are dealing with gigantic phenomena, and we must allow 
adequate causes. 
It is a natural suggestion, that if the Dartmoor granite ever 
passed upwards into volcanic equivalents of the acidic series, 
some of these rocks ought to be found. Considering the enormous 
amount of denudation to which the area has been exposed, and 
the comparatively small proportion these rocks would bear to 
the main intrusive mass, their absence, however, could be 
accounted for. Professor Judd has shown that in Ben Nevis, 
a volcano of the newer Palaeozoic period, much of the same date 
as Dartmoor, we have resting on the basal mass of coarse-grained 
porphyritic granite, and graduating thence, a fine-grained granite, 
graduating into felsite, which in turn sends veins into the fine- 
grained granite, and is surmounted by felstone lavas and volcanic 
agglomerates alternating; the whole existing upper series being 
comprised in an upward range of 2000 feet only. 
The preservation of these volcanic rocks is quite exceptional at 
