ETHERIDGE DEVOXIAI^ ROCKS AND FOSSILS. 



569 



3. Helesbo rough. 



4. Ilfracombe District. 



5. Lae and Morte Bay. 



6. Conclusions relative to the 

 Middle Devonian or Ilfra- 

 combe Grroup of West Somerset 

 and North Devon. 



V. Palseontological Value of the Or- 

 ganic Remains found in the 

 Devonian Groups. 



1. Chronological Equivalents of 

 the Old Red Sandstone of 

 Hereford, Scotland, &c. 



2. Lower Devonian Fossils of 

 West Somerset and North 

 Devon. 



3. Fossils of the Middle Devo- 

 nian or Ilfracombe Group. 



4. Species common to the Middle 

 Devonian Rocks of North 

 and South Devon. 



5. Species common to the Middle 

 Devonians of North Devon, 



South Devon, and West So- 

 merset. 



6. Agreement of Foreign Devo- 

 nian species w^ith the British 

 Middle and Upper Series in 

 North and South Devon. 



7. Analysis of the British and 

 Foreign Devonian Brachio- 

 poda. 



8. British Devonian and Car- 

 boniferous Brachiopoda. 



VI. Stratigraphical Value of the Spe- 



cies comprising the Devonian 

 Fauna. 



1. Amorphozoa. 



2. Coelenterata. 



3. Crustacea. 



4. Cephalopoda. 



5. Brachiopoda. 



6. Other Classes. 



VII. Stratigraphical considerations on 



the Devonian Fossils. 



I. Inteoduction. 



It seems almost superfluous that another paper should be written 

 upon the structure and succession of the Rocks of " West Somerset 

 and North Devon ;" but of late their position or place in the 

 geological series has been questioned in an able paper by Pro- 

 fessor Jukes*, in which he endeavoured to prove that the entire 

 series of slates, sandstones, and limestones of the North Devon and 

 West Somerset area belong partly to the Old Red Sandstone and 

 partly to the Carboniferous rocks, rather than to the so-called Devo- 

 nian Group, to which they have hitherto been considered to belong. 

 In other words, Professor Jukes has propounded views as to the re- 

 lative succession and physical structure of North Devon diametrically 

 opposed to those held by most geologists, and based upon the investi- 

 gations of Sir Roderick Murchison and Professor Sedgwick, Professor 

 John Phillips, De La Beche, Weaver, and others ; and he distinctly 

 states that they have " all misunderstood the structure of the 

 country," and this arising chiefly from their having been previously 

 unacquainted with the structure and succession of the lower mem- 

 bers of the Carboniferous group of rocks, and with the upper series of 

 the Old Red Sandstone, as shown in the South of Ireland (the Irish 

 Old Bed Sandstone). 



Professor Jukes also disputes the reality of the " time " succession 

 (not the apparent) of the rock-groups of North Devon, ^. e. those 

 grits, slates, and sandstones which occur (in the Lynton area) from 

 Lynton or the Foreland, on the north, to the base of the Pickwell 

 Down or Morte sandstones, on the south, or more extendedly to 

 Barnstaple, which is the extreme southern part of the North Devon 



* Quart. Journ. Geol. Soc. vol. xxii. p. 321. August 1866. 



