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MAJOR A. E. DWERRYHOTTSE OX THE [vol. lxxix, 



Tyrone rocks, there is reason to believe that the upper one came 

 from the west. It was probably formed, not by the direct action 

 of the western ice, but because the head of the Scottish lobe which 

 penetrated the Belfast Valley was deflected eastwards by the 

 pressure of the Tyrone ice. 



At its maximum extension the Irish ice probably reached the 

 sea at the mouth of the Bann, and possibly from Bushmills to 

 Ballycastle ; but the traces of its maximum extension may have 

 been obliterated by a subsequent re-advance of the Scottish ice, 

 for which there is a considerable amount of evidence. This 

 question will be dealt with later. 



^Fig. 13. — General direction of the ice-movement at a later stage, 

 wlien the Irish ice was at its maximum. 



In an easterly and south-easterly direction the Irish ice reached 

 the sea at Newcastle (County Down), and at Dundalk, crossing 

 the Silurian hills of County Monaghan at elevations up to 

 1200 feet. This stage of the glaciation is shown on the map 

 (fig. 13). 



After the maximum of the western ice-sheet, the Scottish ice 

 would appear to have re-advanced, but whether in response to a 

 diminishing thrust on the part of its Irish opponent, or to an 



