Wright — Palaeozoic Floor of North-East Ireland. 643 



Probability of concealed Coalfields in the North of Antr 



■im. 



We have now discussed all the possibilities of concealed coalfields within 

 the trough-valley. We know, however, that, to the north of the Highland border 

 ridge, there is another coal-bearing area, of which the exposed coalfield of 

 Ballycastle forms portion. The possibility of a concealed extension of this 

 coalfield occurred to the mind of Alexander McHenry of the Geological 

 Survey of Ireland, and he has suggested in an unpublished report that it 

 will be found to the west, in the direction of Londonderry. He, however, 

 gives no reason for this supposition, and does not suggest any means of 

 locating the best site for exploration. An analysis of the structure of the 

 Palaeozoic floor of this part of the basalt plateau enables us to make such a 

 prediction with a fair amount of confidence. 



It should not be forgotten in connexion with the discussion of matters 

 relating to the Ballycastle field that the coals found in it are in no sense the 

 equivalent of the coals of Dungannon and Coal Island. The strata in which 

 they occur are of Lower Carboniferous age, and are stratigraphically far 

 beneath the horizon of the Coal Measures proper. These strata are, as Hull 

 pointed out in 1871, 1 the equivalent of the Lower Limestone of the central 

 parts of Ireland, and are comparable with the. so-called "limestone-coals" of 

 Scotland. 



The typical Lower Limestone of Ireland is well developed at Dungannon, 

 but when followed northward along the west side of the basalt plateau it 

 becomes gradually intercalated with sandstones and shales, until these pre- 

 dominate to the almost entire exclusion of the limestone. In the Dungiven 

 area small coal streaks also appear, and when we pass east to Ballycastle we 

 find a sandstone and shale series, with well-developed coals, and only a few 

 thin bands of limestone. A similar change probably takes place to the north- 

 east of Dungannon, along the concealed trough-valley, for when we reach the 

 Glasgow district we find a series of shales and sandstones with coals and 

 thin limestones, which can be seen there to occupy a stratigraphical position 

 beneath the Coal Measures and Millstone Grit, similar to that filled by the 

 Carboniferous Limestone in Ireland. 



The Ballycastle field, therefore, contains only Lower Carboniferous coals, 



1 Edward Hull : On the Geological Age of the Ballycastle Coalfield and its relations 

 to the Carboniferous Rocks of the West of Scotland. Journ. R. Geol. Soc, Ireland 

 vol. ii. pt. iii, 1871, p. 260. 



