THE GEOLOGY OF PLYMOUTH. 
453 
Mr. Etheridge, in reply to Mr. Jukes, contended chiefly, but not 
exclusively, on palseontological grounds, that the Devonian rocks 
of North Devon (and therefore from their correspondence those of 
South Devon) are chronologically equivalent to the whole of the 
Old Eed Sandstone. 
And while Mr. Jukes and Mr. Etheridge thus represent the 
extreme views on either side, there are various shades of opinion 
held between. I shall only quote one more hypothesis, and that 
not merely because it is put forward by our most distinguished 
local geologist, but because it seems to me, so far as I have any 
pretensions to form a conclusion on the matter, to represent 
very nearly the exact state of the case. Mr. Pengelly, so far 
back as 1863, suggested that the acknowledged Old Eed beds of 
Scotland and elsewhere, with the Devonian beds, collectively but 
not separately, fill up the Siluro-Carboniferous interval, the Lower 
Devonian beds being on the same horizon as those of the Upper 
Old Eed ; and the Middle and Upper Devonian between the Upper 
Old Eed and the Carboniferous. 
The Devonian rocks, whatever view may be taken of their col- 
lective position, are generally divided into three groups — upper, 
middle, and lower, each of which has representatives on either 
side of the great culmiferous trough of the centre of the county. 
Originally the Plymouth rocks were classed as Lower Devonian. 
They now rank as Middle, with the rocks of Ilfracombe, Bradley 
Yalley, Wolborough, Babbicombe, Dartington, Eerry Head, and 
other limestone districts ; those of Lynton, Meadfoot, Mudstone, 
Looe, Polperro, and Eowey being Lower ; and those of Petherwin, 
Eaggy Point, Pilton, Tintagel, &c, Upper. The Devonian rocks 
of Plymouth may be treated as subdivided by their limestones into 
upper, middle, and lower likewise. 
Let us for a moment recapitulate the conclusions at which we 
have arrived. The centre of the county is occupied by strata of 
Carboniferous age, with the granite of Dartmoor on their southern 
flank. Northward and southward the Carboniferous area is bounded 
by Devonian rocks. On the east Triassic — New Eed Sandstone — 
rocks extend from Watchet to Torquay, with a singularly irregular 
outline. Eastward again, in the corner next Dorset, a compara- 
tively small surface is occupied by Liassic and Cretaceous deposits. 
With these latter we have little to do ; but there is a small 
patch of Metamorphic rocks between the Start and the Eolt Tail — 
