630 Scientific Proceedings, Royal Dublin Society. 



It is recognized of course that these terms are not comprehensive, since the 

 Palaeozoic floor contains also metamorphic and igneous rocks, and the Mesozoic 

 cover is itself overlain in places by Cainozoic sediments and lavas. They are, 

 however, expressive of the fact that the British Isles are composed of a plat- 

 form of older rocks on which newer strata have been laid down unconformably, 

 and emphasize the great period of folding and denudation which separated 

 the Palaeozoic and Mesozoic Periods. 



The Carboniferous strata form the uppermost member of the Palaeozoic 

 sequence. At the end of Carboniferous times came the great period of folding 

 and faulting known as the Hercynian. The consequent uplift resulted in subr 

 aerial erosion and denudation, and a peneplain was cut across the upturned 

 edges of the Palaeozoic strata. The Coal Measures, being the uppermost 

 member of the Carboniferous formation, were in general only preserved in the 

 synclinal basins, where they escaped denudation. On this peneplain were laid 

 down the Mesozoic and Cainozoic sediments, which at one time covered a much 

 wider area than at present. In Miocene times there occurred another great 

 episode of folding and faulting, with uplift and consequent denudation. This 

 denudation stripped off a good deal of the Mesozoic cover, exposing the 

 Palaeozoic floor below and denuding it in turn. 



It is important to realize that it was this latter period of denudation 

 which was largely responsible for the difference that exists between England 

 and Ireland as regards the scarcity of coal. It is generally considered that it 

 was not until the Miocene period that the North Atlantic oceanic basin was 

 formed. During the Hercynian uplift high land lay to the north and west 

 of Ireland, which stood, relatively to the base level of erosion, in as favourable 

 a position as England, and probably at the end of thepeneplanation contained 

 just as many coal-basins. After the Miocene uplift, on the contrary, a powerful 

 drainage was initiated towards the Atlantic basin. At this period were formed 

 the submerged fjords and rias of western Europe, and valleys were excavated 

 to considerable depths below the present sea-level. These valleys have been 

 cut in the Eocene lavas as well as in the older rocks, so that it is clear that 

 they are not referable to any previous epoch. Ireland, being nearer the edge 

 of the Continental shelf, suffered, as a consequence, far more heavily than 

 England. To the Miocene denudation, therefore, we owe, not only the strip- 

 ping off of the Mesozoic cover, but also the removal of much of the Palaeozoic 

 floor itself with its contained coal-basins. The practical conclusion to be 

 drawn from this is that, where the Mesozoic cover is preserved, we might 

 reasonably expect the Palaeozoic floor to be as rich in coal-basins as it is in 

 corresponding parts of Great Britain. 



Turning now to the consideration of the problem before us, we find it is 



