QUATERlsrARY DEPOSITS OF BRITISH ISLES BROOKS. 343 



eating subaerial erosion are developed on the Porcupine Bank and 

 other points off the west of Ireland, and banks of dead shells of 

 littorial type occur elsewhere on the continental shelf; the sea bot- 

 tom here presents an interesting contrast to the drift-encumbered 

 floor of the sea between Scotland and Ireland. 



If the tilting which causes the 25-foot raised beach to descend from 

 30 feet at Malin Head to sea level at Donegal, were prolonged for 200 

 miles to the southwest, it would result in an elevation there of nearly 

 90 feet. 



I have already alluded to the submerged peat frequently observed 

 to extend below the level of spring low tides on the west coast, and 

 pointed out that this elevation must extend well into the neolithic 

 period; there is other evidence which brings the final subsidence 

 down to a much later date. The Rev. W. Kilbride, proved that at 

 Tramore, on xVran Island, human habitations extend below spring 

 low tides level, and the ancient annals have accounts of the " bursting 

 forth " of lakes, so that fresh-water loughs became arms of the sea, 

 owing to the sinking of the intervening land. Galway Bay is men- 

 tioned as an example. (Kinahan, 1878). That this is not merely a 

 case of marine erosion is further shown by the case of Lough Corril, 

 which according to tradition was formerly only one-half of its pres- 

 ent size — ^this reduction would have been effected by raising it 15 

 feet. Finally we have the tradition of Atlantis, the island to the 

 southwest of Ireland, whose mythical existence thus finds strong sup- 

 port. 



East and northeast of this area of high land lay the region of 

 jnaximum submergence in late glacial times, but it is difficult to ex- 

 plain the aiDparently abrupt disappearance of all the beaches. The 

 100-foot beach has not been traced west of Horn Head, where it is 

 about 70 feet above the sea. Probably the boundary between the 

 regions of elevation and of considerable depression was an unstable 

 zone in which the shore never remained at one level long enough for 

 the development of noticeable rock shelves or terraces. In any case 

 the north coast of Donegal has not yet been examined in sufficient 

 detail. 



Even more remarkable is the fact that no record has yet been made 

 of the high level beaches in the district around Belfast, although 

 the Geological Survey has recently reexamined the superficial geol- 

 ogy. It is possible that the beaches were formed there and subse- 

 quently removed by denudation, but the number of sheltered loughs 

 and estuaries renders such complete removal improbable. The alter- 

 native is that the beaches were "formed and still exist, but the resul- 

 tant of subsequent movements has left them at sea level. That this 

 is the case we have strong evidence in the occurrence of the gray 

 marine sands of the Belfast district, already described; like the 



