IN THE NORTH OP lEELAND. 



831 



fortiori, further inland, hinder a northward movement; and it follows 

 that we find striae in Tyrone, Fermanagh, Mayo, &c., bearing 

 south of west, all obviously due to the prevalence of a Scottish ice- 

 system over the Irish, so far southward as the occurrence of west- 

 ward striae warrant us to predicate its influence. Confirmatory 

 evidence for the westward movement is to be found in the absence 

 of granitic blocks from the Lower Boulder-clay of Glen Swilly*, and 

 from the boulder-clay which rests on the granite at the north 

 entrance of Barnesmore Gap. Hence the ice-sheet which passed off 

 the Wigton and Ayrshire coast flowed on to Irish soil, and urged its 

 way across the country, bearing previous accumulations before it, to 

 escape on the western coast by the various bays of Donegal, Sligo, 

 Mayo, and Galway, and over mountain groups which were unable to 

 command an independent glacial system sufficient to obstruct or 

 divert its flow. Dr. Hull considers that a glacial s3'Stem, centred in 

 the Mourne Mountains, presented such an obstacle : and this would 

 account for an absence of westward striae south of the Strangford- 

 Lough and Galway-Bay line. 



The Irish Glacial System (Map, fig. 2). — Much has been done by 



Fig. 2. — Map of the North of Ireland., shoiving the North-Irish 

 system of glaciation, after Professor Hull. 



the Eev. M. Close towards the elucidation of glacial phenomena in 

 the Irish area f ; and his map of the glaciation of larconnaught, 



* As observed by Mr. M'^Henry. 



t Paper on the " General Glaciation of Ireland," with Map, Journ. Eoj Sec. 

 Irel. vol. i. new series, p. 207. 



