382 TRANSACTIONS OP SECTION C. 



3. The Glaciation of the North-East of Ireland. 

 By Arthur R. Dwerryhouse, D.Sc, F.G.S. 



The district under consideration consists of the Basaltic Plateau of County 

 Antrim, the Silurian Uplands of County Down, the granitic Mourne Mountains, 

 and the Valleys of the Bann and the Lagan, the former including the Lough 

 Neagh Basin. 



That the area was overridden by Scottish ice at the period of maximum 

 glaciation has been known for some time, the Riebeckite-Eurite of Ailsa Craig 

 being found in the boulder-clay and gravels, but the glaciation has not hitherto 

 been worked out in detail, with the exception of that of the Belfast district, of 

 which the Geological Survey has published a drift map. 



At the period of maximum glaciation the country east of Lough Foyle, the 

 Sperrin Mountains, and Slieve Gallion was completely covered by the Scottish 

 ice, most of which travelled down the Firth of Clyde, and is here spoken of as 

 the Firth of Clyde Glacier. 



During the period of retreat the Firth of Clyde Glacier impounded the 

 drainage of the district, and brought about the formation of a number of lakes, 

 the overflow channels of which, ' dry gaps,' mark the various stages in the 

 shrinkage of the ice. 



The earliest channels appear to be on the northwestern flanks of the Mourne 

 Mountains at an elevation of about 1,200 feet, with others at lesser altitudes, 

 one of the largest being between Corlieve Mountain and Tievedockaragh at 684 

 feet above sea-level. 



As the ice-margin shrank northwards numerous ' dry gaps ' were produced 

 along the lower slopes of the Mournes and also through the granite hills of the 

 Slieve Croob Range to the North. 



Numerous other series of channels can be traced, produced as the ice-front 

 fell back, a mast interesting stage being reached when the Antrim Plateau was 

 free from ice except along its seaward margin. The Valleys of the Bann and 

 Lagan were closed near their mouths, and the then more extensive Lougli 

 Neagh drained through the now streamless valley at Poyntzpass to Newry and so 

 into Carlingford Lough, and at another stage by Monaghan, Smithborough, and 

 Clones into the Valley of the Erne. Still later, Lough Neagh, which was then 

 continuous with the Lake Belfast of the Geological Survey, drained through the 

 Dundonald Valley from Belfast to Newtownards and so into Strangford Lough. 



The effects of the Firth of Clyde Glacier are to be seen in the presence of 

 erratics from Ailsa Craig and Arran, some of the latter having been recognised 

 by Mr. B. N. Peach when going over the ground with the writer in the uplift 

 of boulders and in the transport of local erratics. 



Many examples of the diversion of rivers by morainic material also occur, 

 the most interesting being those of the Bush River near Annoy and the Glenaan 

 River near Cushendall. 



It has been stated that the Antrim Plateau was glaciated by local ice after 

 the retreat of the Firth of Clyde Glacier, but the writer has failed to find any 

 direct evidence of this in the northern part of the area, though the valleys of 

 the Sperrin Mountains to the west were occupied by local glaciers. 



4. The Glacial Period and Climatic Changes in North-East Africa. 

 Bij W. F. Hume, D.Sc, F.R.S.E., and J. I. Craig, M.A., F.F.S.E. 



1. Southerly Shift of the Wind -systems in Glacial Time.". — The effect of the 

 seasonal decrease of temperature in the Northern hemisphere is to cause a sea- 

 sonal displacement of the system of westerly moist winds southwards by several 

 degrees, and not improbably decrease of temperature below its normal is also 

 associated with a similar displacement. It is inferred that the decrease of tem- 

 perature of the Glacial Period would be correlated with such a displacement of 

 the westerly winds, which now barely touch the north coast of Egypt in winter, 

 that they would impinge on the loftiest portion of the Red Sea mountain range. 



Geological and topographical evidence points conclusively to the existence of 

 such a westerly moist current at no very distant period. The current was 



