Professor G. A. J. Cole — The Structure of Ireland. 4:b7 



Cambrian, oi" older; and gneiss is included in the granite of eastern 

 Tyrone, the latter being probably of Caledonian age. The gneiss of 

 the ancient moorland between Oraagh and Cookstown is, moreover, 

 very possibly pre-Cambrian. The Silurian sea must have covered 

 all the Irish area ; and the subsequent Caledonian folding, with its 

 axes running north-east and south-west, marked out the first distinct 

 lines of the existing country. The arches became filled with molten 

 rock as they rose, and denudation has again and again exposed in 

 them a core of granite. To this folding we owe the guiding lines 

 of Donegal, Sligo, and Mayo; the axis of Newry, which reaches 

 from the sea — and, indeed, from Scotland — down into the midland 

 counties; and, above all, the long mass of the Leinster Chain, the 

 most important feature of south-eastern Ireland. The granites 

 weather into round-backed moorlands ; the schistose foothills give 

 rise to picturesque ridges and ravines upon their flanks. In the 

 Dublin area, between the foothills and the sea, quartzites and slates, 

 usually regarded as Cambrian, have added the prominent features of 

 Howth, Bray Head, and the two Sugarloaves, to an already diversified 

 landscape. 



The Old Eed Sandstone lakes spread across the hollows of the 

 Caledonian continent, to be succeeded by the inflow of the Carboni- 

 ferous sea. The Lower Carbonifei'ous beach-deposits are now found 

 on the summits of west Irish mountains, and very little of the 

 country can have escaped submergence. The Hercynian folding 

 produced the second series of structural lines, assisted by the varying 

 resistance of the Old Eed Sandstone and the Carboniferous Limestone 

 to denudation. The east-and-west anticlinal ridges, from the Atlantic 

 to the Irish Channel, with intervening valleys, where the limestone 

 is protected in the synclinals, repeat on a bold scale the structure of 

 South Wales and Belgium. The folds swung round in the neigh- 

 bourhood of the pre-existing Leinster Chain ; and the axis of the 

 Kilkenny Coalfield, where the Coal-measures remain on a high 

 synclinal, runs north-east and south-west, like its neighbour on the 

 east. The great limestone plain itself is probably to be looked on as 

 a vast shallow synclinal of the same epoch, into which, in later 

 periods, the Caledonian and Hercynian ridges. .poured down their 

 detritus. 



Marine Permian beds occur near Stewartstown, south-west of 

 Lough Neagh, and also in the north of County Down. The 

 terrestrial conditions of the British Trias were continued into the 

 Irish area, but the remaining beds of this period all lie north of 

 Dublin, and mostly owe their preservation to the capping of Cainozoic 

 basalt. The Ehgetic sea penetrated as far west as the Caledonian 

 hills of Londonderry, and marine conditions continued during early 

 Liassic times. An uplift then probably occurred, and the sea did 

 not return till the middle of the Cretaceous period. The 'White 

 Limestone,' which forms so distinctive a feature of the Antrim coast, 

 represents the English Chalk. 



The great feature of the north is, however, due to volcanic 

 eruptions of Eocene age. Owing to the immense outpouring of 



