PENGELLT — FOSSILS OF DEVON AND CORNWALL. 
11 
Scotland does not yield the mollu.sks or zoophytes of Devonshire, 
nor is there recorded in the latter district more than the faintest 
trace of the ichthyolitic wealth of the North. Though this fact may 
still have difficulties connected with it, they have ceased to be 
chronological, for JSir R. 1. Murchison tells us "that the same fossil 
fishes, of species well known in the middle and upper portions of the 
Old Ked of Scotland, and which in large tracts of Kussia lie alone 
in sandstone, are in many otlier places found intermixed, in the 
same bed, with those shells that characterize the group in its slaty 
and calcareous form in Devonshire, the Rhenish country, and the 
Boulonnais. This phenomenon, first brought to light in the work 
on Russia, by myself and colleagues, demonstrates more than any 
other the identity of deposits of this age, so different in lithological 
aspect, in Devonshire on the one hand, and central England and 
Scotland on the other. The fact of this intermixture completely 
puts an end to all dispute respecting the identification of the central 
and upper masses at least of the Old Red of Scotland with the cal- 
careous deposits of Devonshire and the Eifel."* 
In a paper "On the Slate Rocks of Devon and Cornwall," read 
before the Geological Society of London in 1851, Professor Sedgwick 
stated his views respecting the division of these rocks into three 
groups, as follows : — 
" The first and oldest of these groups may be conveniently called 
the Plymouth group, using these words in an extended sense, so as 
to include all the limestones of South Devon, and the red sandstones 
superior to the Plymouth limestones. The equivalent to this group 
in North Devon includes, I think, the Ilfracombe and Linton lime- 
stones, as well as the red sandstones of the north coast. 
" The second group includes the slates expanded from Dartmouth 
to the metamorphic group of Start Point and Bolt Head, and is, so 
far as I know, without fossils ; it may be called the Dartmouth group, 
and its equivalent in North Devon is found in the slates of Morte 
Bay, which end with beds of purple and greenish sand-rock and 
coarse greywacke. It ranges nearly east and west across the 
county. 
"The third group is not, I think, found in South Devon; but in 
North Devon it is well defined, commencing on a base line of sand- 
stone beds, which range nearly east and west from Baggy Point (on 
the western coast) to Marwood (which is a few miles north of Barn- 
staple), and thence towards the eastern side of the county. This 
group is continued in ascending order to the slates on the north 
shore of Barnstaple Bay ; but its very highest beds are seen on the 
south shore of the bay, dipping under the base of the culm measures. 
" The equivalent of this third and highest Devonian group is found 
to the south of the great cidm-trough, in a group, near the top of 
which appear the limestone-bands and fossiliferous slates of Pether- 
win. It may be called the Barnstaple or Petherwin group.'"'\ 
* ' SiluHa,' 3rd edition, p. 382. 
t Quarterly Journal Geol. Soc. vol. viii. p. 3. 
