646 Scientific Proceedings, Royal Dublin Society. 



by the intersection of the direct and transverse synclines to the west. This 

 is the occurrence of the fault known as the Great Gaw, which has an approxi- 

 mately east and west course from Murlough Bay to Ballycastle. This fault 

 has an immense downthrow to the north, certainly well over 1000 feet, but 

 probably as much as 2000 feet. All the really valuable seams occur only to 

 the north of it. Its extension to the west from Ballycastle follows the line 

 of the Ballycastle Railway for about two miles, and then turns west again by 

 Moss-side towards Coleraine. In this part of its course it serves to bring in 

 the area of Upper Basalt between Coleraine and Ballycastle. Its throw in 

 the Mesozoic and Tertiary rocks is not so great as in the Carboniferous. 

 Thus at Murlough Bay it only displaces the chalk about 100 feet. South- 

 west of Ballycastle it has a downthrow of about 700 feet to the north-west, 

 as shown by the displacement of the chalk and basalt. Further west its throw 

 is difficult to determine, but is probably not as great as this. It is clear, how- 

 ever, that the post-Basaltic displacement is only the result of posthumous 

 movement along the fault, and probably indicates a much greater throw in 

 the Carboniferous beds beneath. The main portion of the displacement, 

 having therefore taken place previously to the pre-Mesozoic denudation of 

 the Palaeozoic floor, tends to the preservation of a greater thickness and area 

 of coal-bearing strata to the north. A similar incoming of higher Carboni- 

 ferous strata probably accompanies the parallel fault running from White 

 Park Bay to Port Ballintrae, which also has a downthrow to the north. 

 These faults, it will be noted, are not parallel to the Dungiven-Ballycastle 

 and Lough Foyle synclines, but cross them obliquely in exactly the same 

 manner as the Coal Island and Templepatrick fault and those parallel to it cross 

 the trough-valley. In this instance, however, they have downthrows to the 

 north, so that it is desirable, having due consideration for the other factors 

 involved, to keep as far north as possible in all preliminary explorations. 

 This makes the northern or Lough Foyle syncline a decidedly better proposi- 

 tion than the Dungiven-Ballycastle one. It also makes it worth our while to 

 consider the anticlinal area between Coleraine and Ballintoy as a possible 

 coal-bearing area. 



As regards the Dungiven-Ballycastle syncline, which lies, except in the 

 northern part of the Ballycastle field, to the south of the fault, I am never- 

 theless inclined to take a very optimistic view ; for although the strata seen 

 in this syncline at Dungiven, and at Ballycastle to the south of the fault, con- 

 tain only small coals, and are stratigraphically undoubtedly beneath the richer 

 seams, yet, if we can judge from what takes place at Coal Island, covering strata 

 will be taken on at such a rate when we pass into the area of intersection with 

 the Bann transverse trough, that the higher beds containing the thicker seams 

 are very likely to be preserved, 



