644 Scientific Proceedings, Royal Dublin Society. 



and in considering the problem of a possible concealed extension of this field 

 we have three things to think of: — 



1. Where, according to the tectonic structure of the district, is such an 

 extension likely to occur ? 



2. Are the coals likely to have deteriorated in this extension ? 



3. Are the Coal Measures proper likely to occur above the Ballycastle 

 series in such an extension ? 



In the first place, it is important to realize that the -exposed portion of 

 the Ballycastle field is only a portion of a much larger field, extending to the 

 north, beneath the sea. This fact is apparent to anyone who has examined 

 the fine coast-sections which foim its northern limit, and is borne out by the 

 fact that a similar series with coals and limestones occurs at Machrihanish, near 

 Campbelltown, in a position on the north side of the Highland border ridge, 

 very similar to Ballycastle. One gets the impression, therefore, that there 

 is an extensive coal-basin to the north-west of this ridge. In order to form 

 an idea of its structure we must follow the ridge throughout its course, and 

 see what takes place to the north of it. 



The Ballycastle- Dungiven and Lough Foyle Synclines. 



In the first place, the Ballycastle coalfield is in the form of a syncline, 

 the strata dipping north off the schist ridge, and rising again towards the 

 coast. When we pass west, across the transverse synclinal trough of the 

 Bann Valley, to the western escarpment of the basalt plateau, we find a 

 similar syncline lying to the north of the ridge at Dungiven. To the north 

 of this, at Ardmore, between Dungiven and Limavady, is an anticline of 

 schist, and then comes the larger Carbonifeious syncline of Lough Foyle, 

 bounded to the north by the schist ridge of Inishowen, the rocks of which 

 correspond to those of Islay and Jura in Scotland. "We thus get the impres- 

 sion of the basin as being made up of two synclines and an intervening 

 anticline, all with their axis parallel to the Highland border ridge, the 

 Ballycastle syncline and the Dungiven syncline being probably portions of 

 the same tectonic feature. Along the same line, further west, occurs the 

 very marked synclinal Carboniferous basin of Donegal Bay, which corre- 

 sponds to one or both of the Co. Deny synclines. 



We have now to consider the effect on these synclinal basins where they 

 are crossed by the transverse synclines and anticlines described above in 

 connexion with the Lough Neagh and Larne coal-basins in the trough- valley. 

 In the first place, it is to be noted that the Ballycastle coalfield occurs just 



