7 8 Proceedings of the Royal Irish Academy. 



What has been said of Bengower, Shannaunnafeola, and the neighbouring 

 mountains is equally true of many other of the mountains of the 'western 

 liighlands ; and if evidences of glaciation have not been observed more 

 frequently, it is because the markings are either hidden beneath peat or 

 drift, or have become obliterated by the ordinary processes of weathering. 

 Even on Clare Island, where the uncovered rocks are not particularly 

 well calculated to withstand the weather, the rounded forms of roches 

 moutonnees are still in evidence as high as the 600-foot contour-line on the 

 shoulder of Knocknaveen. 



It is certain that phenomena such as those described could not have been 

 produced by the action of local mountain glaciers, and it becomes necessary 

 to postulate a regional ice-sheet of considerable dimensions. What has been 

 the origin of such an ice-sheet, and whence has it come, are questions which 

 involve us in the consideration of an extraordinary episode in the recent 

 geological history of northern Europe, that of the Glacial Epoch. At a 

 distant period, impossible to reckon in years, but somewhere at the close of 

 the Tertiary Epoch, arctic conditions set in over the whole of the northern 

 portion of the European continent. Snow accumulated on the great Scandi- 

 navian plateau, and being converted into ice, flowed outwards, under the 

 influence of gravity, from that axis in all directions. As the cold became 

 more intense, the snowfall increased, and the Scandinavian glacier, enriched 

 by coustant and increasing accessions of glacial material, drained into the 

 North Sea and Baltic basins, finally extending southwards as far as the 

 50th parallel X. lat. The ice, having filled the basin of the Xorth Sea, 

 invaded the British area, as is proved by the boulders of Xorwegian and 



lish porphyries, gneisses, granites, &c, which have been found embedded 

 in the drifts of the east of England. As no Scandinavian boulders have been 

 found in Scotland, it is inferred that the ice which gathered on the Scottish 

 Highlands was sufficiently massive to bar the progress of the glacier from 

 the Xorth Sea. The two ice-sheets therefore coalesced to form a continuous 

 ice-cap which buried the whole of Britain as far south as the valley of the 

 Thames. As the Scottish ice developed, it drained freely from its ice-shed 

 westward]} - and south-westwardly into the Atlantic Ocean, the Xorth 

 Channel, and the Irish Sea, and appears to have swept over the north-east 

 of Ireland, scoring and polishing the rocks in its path, and bringing along 

 with it many varieties of foreign boulders from the Scottish area. It is 

 probable, however, that it did not push its way far inland ; its progress was, 

 no doubt, soon arrested by the increasing glacial accumulations of a central 

 Irish ice-field, and the current was deflected into the Irish Sea and Atlantic 

 Ocean. 



