640 Scientific Proceedings, iioyal Dublin Society-. 



Carboniferous beds along this belt can in some cases be proved to be greater 

 than that of the overlying Mesozoic rocks, as, for instance, in the Coal Island 

 area, where the Coal Measures have been reached by shafts sunk through the 

 Triassic sandstones. Much of the faulting which affects the Carboniferous for- 

 mation is, moreover, clearly pre-Mesozoic ; and even in those cases where a 

 fault is continued in the Mesozoic rocks, it can be shown to displace them to a 

 much smaller extent than it does the Carboniferous strata. For example, the 

 great fault, which limits the Coal Island field on the north, and has, according 

 to Hardman, a throw of over 2000 feet, when continued to the east into the 

 Mesozoic rocks and lavas, displaces them at the most about 1000 feet. The 

 cumulative effect of the folding and faulting in the Carboniferous rocks along 

 the western margin of the plateau is to cause them to take on cover in the 

 direction of the Bann syncline at a much greater rate than would be the case 

 if they were merely affected by the post-Mesozoic folding and faulting. We 

 can see, in fact, one side of the pre-Mesozoic syncline, and are thus assured 

 of its existence. We merely use the posthumous folding along the same line 

 as an indication of its limits where it is concealed. 



We may, therefore, take the established limits of the post-Tertiary trough 

 to indicate the existence of an extensive coal-basin, of which we see a mere 

 fragment in the exposed field of Coal Island. The general position and outer 

 limits of this coal-basin have already been indicated. The centre of the 

 basin and the greatest thickness of coal-bearing strata lie beneath Lough 

 ISfeagh, where the median line of the transverse syncline crosses the trough- 

 valley. It is situated most probably in the south-east of the trough -valley, the 

 north-western half, which is elsewhere occupied by Old Eed Sandstone, being 

 less likely to contain Coal Measures. We have seen, however, that in this 

 particular area the Lower Carboniferous strata transgress the area of Old 

 Red Sandstone, and there is at least a chance that, in the very centre of the 

 transverse syncline, the Coal Measures may do so too. Search should, 

 however, in the first instance be confined to the south-eastern portion of 

 the area. 



It is not perhaps to be expected that the indicated area will everywhere 

 coutaiu Coal Measures right up to its margins. Owing to the highly faulted 

 character of the ground, blocks of Lower Carboniferous strata will probably 

 come to the surface of the Palaeozoic floor here and there. Indeed the south- 

 western corner of the area, which is partly exposed, contains a large propor- 

 tion of these lower beds. We see therefore that to have the greatest chance 

 of success the first bore-holes should be located as near to the centre of the 

 depressed block as is possible under the circumstances. Were it not for the 

 engineering difficulties, the best site for boring would be in the centre of the 



