OF THE ROCKS OF THE SOUTH OF IRELAND. 263 



South of Ireland, only requires a brief notice here. These beds 

 having been repeatedly described by previous writers, from the 

 Rev. 1). Williams * and Mr. Weaver f down to Messrs. Townshend 

 Hall X and Etheridge | in more recent times, I here give descrip- 

 tions taken chiefly from my own note-book. The beds are described 

 in descending order : — 



(1) Mortchoe Slates. Glossy micaceous slates, uniform in texture, and 

 such as might have originated from the waste of gneiss or mica-schist: 

 unfossiliferous. 



(2) Ilfracombe beds. A variable series of grey slates and thin grits, con- 



taining numerous bands of blue earthy limestone (" Stringocephalus- 

 limestone "), chiefly in the lower part. These beds are highly fossili- 

 ferous, containing polyzoa, corals, and mollusca in abundance. 



(3) Hangman Grits (Martinhoe beds of T. M. Hall). Hard, fine-grained, 



red, purple, and grey grits with bands of slate rising from below the 

 Ilfracombe slates at Combe-Martin Bay. These beds, like those of the 

 Pickwell-Down Sandstones, form high tablelands or downs, traversed 

 by deep dells leading down to the sea. 



(4) Lynton Slates. Greyish sandy slates and fine grits, cleaved, passing 



down into calcareous banded slates and earthy limestones, highly 

 fossiliferous. These beds break oif into scarped cliffs, ridges, and tors 

 along well developed planes of jointage. Corals, polyzoa, crinoids, 

 spirifers &c., are abundant. 



(5) Foreland Grits. Massive coarse- and fine-grained grey, purple, and 



green grits, with bands of schist. Pebbles of quartz, quartzito, and slate 

 sometimes occur. The beds are contorted, and their base is nowhere 

 visible §. Fucoid and linear plant-remains occur, resembling those 

 from the GlengarifF beds of Ireland. 



Fossils. — The Middle Devonian ; or Ilfracombe beds have yielded, 

 according to Mr. Etheridge, 73 known forms, of which about 20 

 come from the Lower Devonian or Lynton beds ; but only three 

 forms from the Lower, and 28 from the Middle Devonian beds are 

 found in the Carboniferous beds generally ||, and not a single form 

 out of either the Lower or Middle divisions has been discovered 

 in the Glengariff grits or slates of Ireland, with which they have 

 been correlated by some authors. 



lliichiess of heels. — A careful estimate of the thickness of the 

 Devonian beds of jS"orth Devon has been made by the Rev. Dr. 

 Haughton, which, as being the most recent, I here insert, though the 

 question of thickness of strata is not one materially affecting the 

 subject under consideration. Dr. Haughton's estimate 5[ is as 

 follows : — 



(a) Erom the lowest beds at Lynmouth, occupying the summit of 

 the great anticlinal arch, up to the Ilfracombe marine limestone, 

 4400 feet. 



(6) Erom the Ilfracombe limestone to the Cucullcea- and plant-beds 



* Rep. Brit. Assoc. 1839, Trans, of Sections, p. 95. 

 t Proc. Geol. Soc. Lond. vol. ii. pp. 589, 590. 



I Supra cit. See also De la Beche, ' Rep. Devon. Corn. & Somer.' plate 3, &c. 

 § See De la Beche' s section, plate 3, supra cit. In placing the Foreland 



Grits at the base of the Lower Devonian, I adopt at this stage the prevalent 

 view. Further on it will be seen that there is reason for supposing they form 

 the connecting link between the Devonian and Silurian series. 



II Supra cit. pp. 074, G75. 



\ Journ. Roy. Geol. Soc. Ireland, vol. v. (new ser.) pp. 120, 127. 



