456 JOURNAL OF THE PLYMOUTH INSTITUTION. 
Devonian age. This contemporaneity is clearly seen in the railway 
cutting above Weard Quay, not far from Saltash. Here we find a 
series of layers of trap interstratified with slate, more than a score 
in number, and varying from an inch to three feet thick. And 
here, therefore, the lava must have spread itself upon the sea 
bottom in successive sheets with comparative quietude, and at 
intervals sufficiently long to allow of the deposition of considerable 
layers of silt between. 
Taking the whole of these phenomena together, they seem to 
indicate the special local influence of volcanic action, operating 
over a lengthened period. 
I doubt whether the more southerly traps, those next the lime- 
stone, are contemporaneous. They seem rather to be intrusive — 
to have the appearance of being thrust into the positions which 
they occupy. I have no direct evidence to offer, but it is a fact 
worth noting, that the greenstone on the north of the Tealmpton 
limestone is clearly intrusive ; nor do I think the fact that they 
contain large quantities of carbonate of lime without its value. If 
this suggestion be correct, these rocks may probably be of Car- 
boniferous age ; for we know that during this period there was 
a centre of great volcanic activity so near us as Brent Tor. 
Now the whole of these northern rocks, with such exceptions 
as I have indicated, appear to have a constant southerly dip, at 
angles which vary from 80° to 10°, but can hardly be averaged at 
less than 55° or 60°. I say appear, because the cleavage planes 
are mostly well developed, and it is not easy — nay, at times 
impossible — to distinguish between the cleavage and the bedding. 
Still, there can be little doubt that the bedding and cleavage have 
a general coincidence. Are we, therefore, to infer that this single 
sub-section of the Devonian system has such an enormous thickness 
as this regular succession of conformable strata would seem to 
imply — a thickness that would have to be measured by miles ? 
There is no absolute necessity that we should. 
To me these rocks appear to yield evidence of having been 
thrown into numerous folds with a prevailing southerly dip, so 
that instead of having a succession of fresh beds southward, we 
have a frequent repetition. The anticlinals to which I have re- 
ferred would thus be the remnants of such portions of the actual 
flexures as have not been denuded off. There is so remarkable a 
similarity in the slate rocks of this division, that it is by no means 
