530 Pt^of. SuU — On the North Devon Section. 



With reference to tlie bearing of the structure of the South of 

 Ireland on that of Devonshire, I have come away from the examina- 

 tion of the rocks in the former district strongly impressed with two 

 or three leading conclusions. 



First. — That the " Dingle beds " (Grlengarriff grits, etc.) belong 

 in all probability to the Upper Silurian series, a view maintained 

 by Sir R. GrifSth, Mr. John Kelly, and others, including several of 

 my colleagues of the Geological Survey of Ireland. 



Secondly. — That not only in the Dingle promontory, but every- 

 where in the South of Ireland, these Upper Silurian beds are 

 separated by a wide gap (represented by denudation and uncon- 

 formity) from the true Old Eed Sandstone ; and thirdly, that the 

 Old Eed Sandstone is conformable to the overlying Lower Carboni- 

 ferous series ; — a view generally accepted amongst Irish geologists. 



With these Upper Silurian beds (" Dingle beds and Glengarrifif 

 grits "), consisting of conglomerates, red and green grits, and purple 

 slates of great thickness rising into the highest elevations in Ireland, 

 striking generally eastwards until they pass unconformably below 

 the Old Eed Sandstone of Cork and Waterford, the qviestion arises, 

 may we not expect to find them represented in the Devonshire 

 Section ? This, to my mind, seems in the highest degree probable, 

 to say the least of it. Then, again, another question suggests itself : — 

 May there not be some beds in the Devonshire Section which, in that 

 region, occupy the gap between the UpjDer Silurians and the true 

 Old Eed Sandstone in the South of Ireland ? If so, what part of 

 the series would they represent ? Clearly, beds older than the 

 "Upper Old Eed Sandstone," which underlies conformably the 

 Lower Carboniferous beds, and newer than the Upper Silurian ; 

 that is to say, beds in the position of the Marine Devonian beds of 

 Devonshire, including the " Lynton Slates " and Ilfracombe and 

 Mortehoe groups.^ 



Ivlow, the base of this fossiliferous Marine Series is evidently and 

 admittedly "the Lynton Sandstone " (Foreland group). A series of 

 unfossiliferous hard red and green sandstones, or rather grits, with 

 some slaty beds, of which the base is not seen, and which is over- 

 laid by the Lynton slates, full of marine fossils. Jukes describes 

 them in terms strictly applicable to the Glengarriff grits and slates 

 of Kerry, viz. "as thick massive grits of gi'een and red colours, with 

 purple slates, the whole being similar to many parts of the Old Eed 

 Sandstone of the South-western portion of Ireland,"^ by which he 

 means the " Dingle Beds " or " Glengarriff Grits," by him supposed 

 to be " Old Eed Sandstone." Of the beds to which Mr. Jukes refers 

 there can be no doubt ; for when he wrote the above, great un- 

 certainty prevailed regarding the real age of these beds. This 

 uncertainty is now neai-ly removed — and geologists in this country 

 are coming round to the views of the late Sir E. Griffith stated 



1 I use the terms adopted in "Woodward's " Geology of England and "Wales." 

 - Additional Notes on the Grouping of the Eocks of North Devou and "\r\^est 

 Somerset, p. 9, Dublin, 1867. 



