ETnEfilDGE DEVONIAN ROCKS AND FOSSILS. 601 



(4) South of the anticlinal of the valley of the East Lynn, and 

 reposing upon the sandstones, there occurs a series of fossiliferous 

 grey and purple slates and grits, with sub crystalline beds of lime- 

 stone, the whole about 1200 feet thick, in many places rich in 

 organic remains which are characteristic ; but, owing to cleavage and 

 the nature of the matrix and laminction, tliey are badly preserved. 

 These are the Lower Devonian slates — the Lynton group. 



(5) The fauna of this lower group of slaty deposits is purely 

 marine, almost pecuhar to itself, being entirely and importantly dif- 

 ferent from that of the Silurian epoch which preceded it, having 

 only one species said to be common, after the obscure and doubtful 

 forms of Corals and Polyzoa are eliminated ; the remaining fauna 

 sufficiently determines it to be a distinct and great life-period existing 

 between the Silurian below, and the Upper Devonian and Carboni- 

 ferous above. 



(6) The community of species, both of the Lynton or Lower De- 

 vonian group and of the succeeding Ilfracombe or Middle Devonian 

 (to be hereafter mentioned), added to their equally well-defined phy- 

 sical characters, well enable us to unite, but at the same time to 

 separate them, both in this typical Devonian area and in the equally 

 illustrative and allied districts of the Rhenish provinces and Belgium. 



(7) Succeeding these lower slates, and conformable to them, a 

 second great series of red gritty sandstones occurs, nearly devoid of 

 fossils, and parallel to the strike of the lower or Foreland beds ; these 

 are the Hangman, Oare Hill, and Exmoor grits, which consti- 

 tute a base for the succeeding Middle Devonian, or Ilfracombe 

 slates and limestones, but which physically connect the two groups 

 above and below. 



(8) A marked and important difference occurs in the structure 

 of the slate masses, as well as the fossil grouping of these two areas — • 

 a change by which both may be weU correlated and coordinated 

 mth those of South Devon, on the one hand, and the Ehenish, Bel- 

 gian, and French deposits on the other. 



B. Middle Devonian Group. 



1. Heddonh Mouth to Barnstaple. — This traverse across the middle 

 of North Devon was made for the purpose of establishing a compari- 

 son with the succession of beds examined between Dunster and 

 Dulverton in West Somerset, and also with the view of detecting 

 any evidence of the supposed fault, or anticlinal, along the northern 

 base of the Pickwell and Span-Head sandstones, midway between 

 the Yalleys of the Barle and Exe on the east, and Morte Bay on the 

 west ; better sections could also be obtained along this route than 

 over the wilder parts of the Exmoor Forest, which had been partly 

 traversed from Lynton to near Exe Head on the Moor. 



Commencing my observations at the sea at Heddon's Mouth and 

 Highwear Point, I obtained conclusive evidence of the position and 

 presence of the upper partof the Lower or Lynton slates, dipping south, 

 which are here grey, green, and red in colour, and crowded witli 

 Orthis arcuata{0. lon(/isulcata), anidjheTG and there, Chonetes sordida 



