PENGELLT — ON THE AGE OF THE DAETMOOE GEANITES. 13 
and micaceous granite is traversed by elvans of a compact, fine-grained 
stone, presenting no distinct crystallization of any of its constituents, 
and they have evidently been protruded posterior to the consolida- 
tion of the rocks in which they occur. The facts here noticed war- 
rant the conclusion that it (the Dartmoor region) contains granite of 
three distinct ages."* 
More recently Mr. Ormerod, who most assiduously uses the faci- 
lities which his residence at Chagford gives him for the study of this 
subject, has mentioned several localities where granite veins occur in 
the carbonaceous rocks ; he states that, at one place on the river 
Teign, " the veins throw off branches into the adjoining rock, and 
vary in thickness from a thin filament to a breadth of about eighteen 
feet." He adds, that "the veins contain portions from the adjoining 
carbonaceous beds, sometimes so slightly removed from the original 
position that it can be traced ; in the larger veins some of the masses 
are rounded, as if they had undergone attrition, but some (about a 
cubic foot in size) still preserve their angularity." t 
There can be no doubt, then, that the Dartm.oor granites are less 
ancient than the culmiferous beds of North and Central Devon. 
Our next business is to find, if possible, a modern limit to their age. 
Amongst the stratified rocks of the county, the red conglomerates 
and sandstones, which give such a character to the cliffs and soil of 
South Devon, succeed, in ascending order, the culmiferous beds 
already spoken of ; they are the next more modern. Now con- 
glomerates may be regarded as natural museums, in which we are 
likely to find specimens of all pre-existing rocks occurring in their 
neighbourhood, and the fact that any rock existing in a given loca- 
lity has no representative fragment in an adjacent conglomerate, though 
merely negative evidence, would not be a bad, though by no means 
an unimpeachable, basis on which to found the opinion tliat such 
rock is more modern than the conglomerate thus destitute of any 
indication of its existence. Such an opinion, however, would, of 
course, be overthrown by the first fragment which further research 
might bring to light. 
Sir Henry De la Beche says, " The evidence of the Dartmoor 
granite having occupied its present relative position, anterior to the 
early part of the (New) Red Sandstone, is not always so clear as could 
be desired ; for among all the pebbles of the red conglomerate ex- 
tending from Torbay to Exeter, we have not been able to detect any 
portion of it, though the granite ranges so near that part of the red 
conglomerate. In the tongue of red sandstone and conglomerate 
which runs from Crediton, amid the carbonaceous series by North 
Tawton and Sampford Courtney to Jacobstow, Ave have, however, 
detected pebbles like some varieties of Dartmoor granite." :j: 
It must be confessed that this is not a very pronounced opinion in 
favour of the North Tawton pebbles being of Dartmoor origin. lu 
* Gcol. Trans., 2nd series, vol. vi. part ii. p. 477- 
t Quart. Jour. Geoi. Soc, vol xv. p. 192. 
X ' Report ou the Geology of Cornwall, Devon, etc.,' p. 1G6. 
