478 Geological Society : — ■ 



a thickness of two or three thousand feet. The group then received 

 Sir R. I. Griffith's appellation of Carboniferous Slate. The 014 

 Red Sandstone similarly expanded to the west, from a thickness of 

 a few hundred feet in Wexford to one of several thousand feet in 

 North Cork. Slaty cleavage, which shows itself in both these 

 groups on the east, becomes more marked on the west, until they 

 might both be spoken of as clay-slate formations. 



West of Cork Harbour the Carboniferous Slate is covered in one 

 or two places by patches of black slate, which Mr. Jukes believes 

 to be the lower part of the Irish Coal-measures, resting conformably 

 on the Carboniferous Slate, with no very definite boundary between 

 the two, as in North Devon. He believes, accordingly, that as the 

 Carboniferous slate expands towards the west, the limestone dies 

 away from below upwards, and that the beds which are the base of 

 the limestone at Ballea, a few miles west of Cork Harbour, are on 

 the same horizon as the Upper Limestone beds of Waterford, even 

 these uppermost beds disappearing a little further west. He there- 

 fore looks on the Carboniferous Slate, especially in its upper part, 

 as being contemporaneous with the Carboniferous Limestone. He 

 believes that there is a regular consecutive series from the Old Red 

 Sandstone into the Coal-measures, through the Carboniferous Lime- 

 stone in one area, and through the Carboniferous Slate in the other. 



In North Devon the author considered the dark slates and sand- 

 stones which strike from Baggy Point and Croyde Bay by Marwood 

 and Barnstaple to Dulverton, identical with parts of the Carboni- 

 ferous slate of Ireland ; and red and variegated sandstones and slates, 

 rising out to the northward from underneath the grey series, iden- 

 tical in character with the Irish Old Red Sandstone. On a recent 

 visit, however, to the north coast at Lynton, Ilfracombe, and Morte- 

 hoe, he found that those beds also were identical in character with 

 parts of the Carboniferous slate, and contained some of the same 

 fossils as are found in Ireland and in the Barnstaple district, each 

 district having fossils not found in the others. 



These beds, in the absence of any reason to suspect the contrary, 

 would be judged to pass under that Old Red Sandstone. Relying, 

 however, on the conclusions formed in Ireland, Mr. Jukes believes 

 that the central band of Old Red Sandstone must be cut off towards 

 the north by a great longitudinal fault, with a downthrow to the 

 north of some 4000 feet. Mr. Jukes pointed out that this hypo- 

 thesis would do away with the necessity of assigning the enormous 

 thickness to the North Devon rocks which the ordinary hypothesis 

 requires. 



After discussing in general terms the objections that may be 

 urged against the hypothesis, especially the palcEontological ones, 

 he ventured to propose that geologists should no longer include the 

 Old Red Sandstone among the Devonian beds, but confine the term 

 Devonian to beds containing undoubted marine fossils, lying be- 

 tween the top of the Old Red Sandstone and the base of the Coal- 

 measures. Taking their wide range over the world into account, 

 he would even regard the Devonian rocks and fossils as the most 

 general type of that portion of our series, and consider the Carbo- 



