TOPOGRAPHY AND GEOLOGY. 



our area, and their sandy nature has contributed markedly to the scenic 

 features of the south. 



The continental region again sank, and the sea flowed gently in, every 

 year farther and farther, across the borders of the lakes. The Carboni- 

 ferous period dawned. The Caledonian ridges remained long above the 

 level of the waves, in the form of promontories and islands. The sea thus 

 stole round the Leinster Chain, washed, and finally submerged the isles of 

 Bray and Howth, and Lambay, and spread far to westward, dominating 

 even the stubborn hills of Donegal. Patches of Carboniferous sandstone, 

 laid down on the ancient shore, still cap some of the Caledonian masses in 

 the West. The submergence was here less marked, 

 fi r 1 however, and the coal-beds of Ballycastle, in county 



Ballycastle Coal. Antrim, occurring in the lowest Carboniferous strata, 

 show tliat a coast, with its accompanying forests and 

 deltas, was near at hand upon the north. 



The Carboniferous sea was an extensive one — a veritable ocean. Marine 

 life was abundant in it, and foraminifera, corals, and shell-fish of all kinds, 

 formed vast thicknesses of limestone on its floor. Here and there, the 

 muds washed in from the relics of the Caledonian mass rendered the water 

 turbid, and gave rise to the black shaly limestone locally known as calp. 

 Elsewhere, even up to the shore-line, the deposits were remarkable for 

 their purity. It is possible that no great rivers were scouring the adjacent 

 land. The sea-floor went on sinking, the limestone grew in thickness, and 

 to this day it forms the most continuous and most characteristic of all the 

 Irish deposits. 



The period closed with a general uplift, as gentle as that which had 

 admitted the sea across the lakes. On the flats and deltas thus formed, 

 the forests of the Coal Measures grew ; and there is little doubt that at one 

 time they extended far across Ireland. Tree-ferns, and giant club-mosses 

 and horse-tails, the familiar vegetation of that remote epoch, clothed the 

 I.einster Chain, spread westward into Kerry, and sheltered among the 

 Caledonian ribs of Donegal. Very little of the coal that was formed by the 

 decay of all these forests has, however, been left to Ireland. The new 

 wrinklings of the crust wrought havoc with this valuable material (Fig. 2). 



With the close of the Carboniferous period, the third important epoch of 

 earth-movement in Europe gave us the Hercynian folds, so named from the 

 region of the forest-ranges in Western Germany. The general trend of their 

 axes is from west to east. The floor of Belgium, of southern England and 

 Wales, and of southern Ireland, became crumpled from south to north like a 

 cloth pushed back across a table. As the slowly heaving earth-waves met 

 the Caledonian masses, some deviation from the general trend took place, 

 usually producing a conformity with the direction of the earlier axes. Thus, 

 in England, the recoil from the tough old masses of Westmoreland and 

 Wales drove the axis of the Pennine Chain into a north and south direction, 

 perpendicular to that of the southern folds, which are seen in Wales and 



Mountain ridges ^"^^er London. In Waterford, Cork, and Kerry, the 

 „ o ,, east and west trend is distinct and unimpeded ; but 



the Hercynian anticlinal from Limerick to Portarling- 

 ireiana. ^^^^^ including the Slieve Bloom Mountains, follows 



the direction of the far older Leinster Chain. Away, again, in the north- 

 west, it is probable that the antique core of the Ox Mountains served to 

 direct the course of the earth-wave which rose against its slopes in Her- 

 cynian times. 



