PENGELLY — FOSSILS OF DEVON AND COKNWALL. 



11 



Scotland does not yield the molkisks or zoophytes of Devonshire, 

 nor is there recorded in the latter district more than the faintest 

 trace of the ichthyolitic wealth of the ^^orth. Though this fact may 

 still have difficulties connected with it, they have ceased to be 

 chronological, for 8ir H. I. Murchison tells us " that the same fossil 

 fishes, of species well known in the middle and upper portions of the 

 Old Red of Scotland, and which in large tracts of K-ussia lie alone 

 in sandstone, are in many other 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 

 Boulonuais. This phenomenon, first brought to light in the work 

 on Eussia, by myself and colleagues, demonstrates more than any 

 other the identity of deposits of this age, so difierent in lithological 

 aspect, in Devonshire on the one hand, and central Englaud 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 ; ]t 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 culm-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 P ether win group T'^ 



* * Siluria,' 3rd edition, p. 382. 



f Quarterly Journal Geol. Soc. vol. viii. p. 3. 



