94 Correspondence — Mr. Townshend M. Sail. 



developments of limestone bands near Ilfracombe and in West 

 Somerset. It is impossible to fix any definite boundary between tbem. 



Fifthly. The upper beds of the Hangman group are very coarse 

 and siliceous, silvery red-stained shales being sometimes intercalated; 

 the lower beds are generally flaggy and of a grey colour. 



Sixthly. The Lynton zone is represented by grits, generally 

 breaking in even tabular layers, schists, schistose grits, and slates, 

 of a uniform warm grey tint. 



Seventhly. The Foreland grits are generally fine, flaggy, cream- 

 coloured, dull-grey, brown, reddish or greenish grits, with beds of 

 red grit, sometimes massive ; they very seldom contain slates. 



Throughout the series conglomerate is conspicuous by its absence. 

 The Drayton and Slade group, if not another name for the olive 

 slates which form the base of the Pilton beds, below the Cucullcea 

 zone, has no existence ; and if the Cucullcea and olive slates are to 

 be regarded as a separate division, the term Marwood used by Prof. 

 Hull is much the most suitable, owing to the presence of the Hang- 

 man lower down. W. A. E. Ussher. 

 Beak Street, Barnstaple, Dec. 1878. 



THE NOETH DEVON SECTION. 



Sir, — Professor Hull, having depended on the writings of others 

 for his knowledge of the North Devon rocks, has obtained the result 

 which usually follows this method of inquiry. His proposed classi- 

 fication looks, no doubt, very well in print, but there are two or three 

 points to which any one knowing the locality must take exception. 



At page 531 it is suggested that "it will probably be found on a 

 careful re-survey of North Devon, that the Pickwell Down Sand- 

 stones are somewhat unconformable to the underlying beds." Now, 

 as a matter of fact, so far from this being the case, there is a gradual 

 passage from the slates to the sandstones ; first slates alone, then 

 slates with layers of sandstone ; next, sandstones with layers of 

 slate, and finally the Pickwell Down Sandstone itself. With regard 

 to a j-e-survey of this district, it must be remembered that the present 

 map was constructed, not by the Geological Survey, but by De la 

 Beche, working as an amateur ; and the only boundary-line shown 

 on it is that separating the Devonian and the Carboniferous. In 

 1865 I laid down for the first time, on the one-inch scale, the 

 various subdivisions of the North Devon series from personal obser- 

 vations made during the preceding three years. The nomenclature I 

 then published I had occasion to alter shortly afterwards by the 

 substitution of Cucullcea zone for Marwood zone, 1 and the adoption 

 of " Pickwell Down Sandstone" for the upper portion of the Morthoe 

 group. Mr. W. A. E. Ussher, F.G.S., of the Geological Survey, who 

 has now been engaged for some months in mapping the river valleys, 

 informs me that, after going carefully over the ground, he has not 

 only adopted these subdivisions, but also the general horizons as 

 shown on my map. 



As far as the Drayton and Slade beds are concerned, they have 

 been placed by Professor Hull in a most convenient position in his 

 1 For reasons see Quart. Journ. Geol. Soc, vol. xxiii. p. 374. 



