EPOCHS OF THESE INTRUSIONS. 
29 
action of the deluge, cannot be determined) into 
the adjacent beds of diluvial clay." It will perhaps 
astonish many, to be informed that greenstone re¬ 
sembles greatly, certain kinds of lava, poured forth 
in volcanic countries in modern times, and, as that 
substance, while fluid, would naturally insert itself 
between masses of adjacent strata, or being driven 
up bodily from below, would be impacted into the 
very structure of incumbent rocks, so here, instances 
are not deficient, where greenstone occupies crevices 
in other beds, and has evidently effected, at the 
period of its introduction, considerable alteration in 
the aspect and character of the stone into which it 
has been thus insinuated. I observe lastly, that in 
so far as this county is concerned, this theory may 
possibly after mature examination be supported by 
the palpable resemblance to extinct volcanoes, af¬ 
forded by many of the “tors”of Dartmoor, particularly 
North Brent Tor. 
On the w T hole however, the application of this, 
like all other geological theories, involves consider¬ 
able risk and doubt, and it ought at least to be 
remembered, that we are by no means called on to 
compress all the circumstances consistently referri- 
ble to igneous origin, into one occurrence of volcanic 
action, but on the contrary it will not only be con¬ 
venient, but even consistent, to refer the various 
phenomena of this order to consecutive Plutonic 
disturbances. 
But still, it may with reason be inferred from the 
phenomena of igneous action, being so universally 
of the same order, that these events were not scat¬ 
tered through a series of epochs , but confined to one; 
and in the midst of our anxiety as geologists, to throw 
together as many events as possible, that might be 
deemed due to one cause, it may be questioned, 
whether at the times of these eruptions, the entire 
surface of the country were not convulsed, and 
