April, igi8. The Irish Naturalisl. 53 



THE DEVELOPMENT AND DECAY OF THE IRISPI 



SEA GLACIER. 



BY J. DE W. HINCH. 



(Presidential Address to the Dublin Naturalists' Field Club, 



23 January, 1918.) 



A CONSIDERABLE number of glaciers coalesced to form the 

 great ice-sheet which in Quaternary times occupied the 

 basin of the Irish Sea, and spread inland over many districts 

 along its margin both in Ireland and in Britain. The most 

 important of these local glaciers were the ice of the Clyde 

 area in the earlier stages, and later the ice-sheet which had 

 its origin in north-central Ireland. When the Clyde area 

 had become greatly congested by ice from the Scottish 

 Highlands, a lobe of the Clyde Glacier debouched through 

 the North Channel into the Irish Sea basin, crossing in the 

 course of its advance north-east Ulster on the west and 

 Galloway on the east. On reaching the Irish Sea the Clyde 

 Glacier began to unite with ice from the southern uplands 

 of Scotland, from the Cumberland hills, from Wales, and 

 later from the centre of Ireland. 



W^e now reach a point where a modern speculation 

 regarding the growth and movements of continental ice- 

 sheets may be mentioned. Up to very recent times dis- 

 cussion on the Ice Age has been hampered and confined 

 by evidence drawn from the very restricted glaciers of 

 Switzerland and the Himalaya as we know them at the 

 present day. This type of evidence has had a rather un- 

 fortunate effect on certain controverted questions in glacial 

 geology as the movements of the diminutive glaciers of 

 modern times are clearly controlled by local gravity and 

 the contours of the surrounding surface features. Now 

 glacial geologists have been compelled by the evidence in 

 the field to ask for a type of ice-sheet, which in earlier 

 times moved across great tracts of country without any 

 special regard for elevations of moderate height or depres- 

 sions of moderate depth. According to the earlier view, 



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