lEELAND. 387 



for many geological ages succeeding their deposition, during the whole of which 

 the greater part of the island remained above the level of the sea. Evidence 

 of local depression, such as is afforded by ancient peat bogs lying below the 

 sea-level,* is not entirely wanting, but the raised sea-beaches and terraces of 

 Antrim and Dublin are far more striking. The most continuous of these ancient 

 terraces is that which can be traced from Antrim southward as far as AVicklow, 

 and upon which one of the wealthiest quarters of Dublin has been constructed. 

 The average elevation of this ancient sea-beach is 15 feet, and it corresponds in a 

 remarkable manner with the " 25-foot terrace " of Scotland, which, in Professor 

 Geikie's opinion, may have been elevated into dry land since the Roman 

 occupation of Britain. But whatever the extent of these local oscillations 

 of the land, the bulk of the island remained emerged during the whole of the 

 secondary and tertiary epochs. Whilst England, for the most part plunged 

 beneath the ocean, successively received the sedimentary deposits which account 

 for the variety of its geological formations, Ireland, on the contrary, was exposed 

 to the wasting influence of sub-aerial agencies which destroyed its superficial 

 strata. The waste resulting from this denudation was carried away by ocean 

 currents to the sister island, and piled above the vast stores of coal already 

 deposited over the English area, protecting them from sub-aerial waste on the 

 emergence of the land. Thus Ireland stripped herself to clothe her sister. This 

 debt, says Professor E. Hull, ought never to be forgotten. 



The prodigious number of lakes scattered over the surface of Ireland is the 

 necessary consequence of the general configuration of the country. There are 

 lakes in the glens of the mountains, or at their foot, but by far the greater 

 number are to be met with in the plain. The rain falling over a level country 

 soon fills up the depressions in the soil, and in many instances these disconnected 

 sheets of water cover almost as great an area as the solid land which separates them, 

 and it only needs a local subsidence or depression of the surface through the 

 agency of a fault, or the formation of a barrier across the effluent draining them, 

 to combine all these separate basins into a lake of more considerable size. Thus it 

 was through the agency of a fault in the volcanic rocks that Lough Neagh was 

 formed. That lake, although the largest in the British Islands — it covers 153 

 square miles — is very shallow, and notwithstanding that its area is equal to two- 

 thirds of that of the Lake of Geneva, its cubic contents only amount to the twenty- 

 fourth part of those of the Swiss lake.f 



The majority of the lakes which form so prominent a feature of the limestone 

 plain are of chemical origin. Their water contains carbonic acid gas, which dis- 

 solves the limestone in which they are bedded, and carries away enormous quan- 

 tities of carbonate of lime in solution. By this process the lakes are being 

 constantly enlarged. "We have elsewhere described some of the " sinks " and 

 "swallows" met with in the calcareous regions of continental Europe. In 

 Ireland, too, the same phenomena may be observed, though not perhaps on so 



* Kinahan, Quarterly Journal of the Geological Society, i. 1877. 

 f Hardman, Journal of the Royal Geological Society of Ireland, iv. 



