264 Proceedings of the Royal Irish Academy. 



the " eskers " of Tyrone and those of the Central Plain of Ireland. 

 He says : — 



" But the Tyrone eskers are diiCerent in character from those of the 

 Central Plain ; they are very iiregular in level; for example, the esker 

 wliich crosses the Cookstown-Omagh road, near Barony Bridge, rises 

 rapidly np the hillside, and has the aspect of a terminal moraine formed 

 by a glacier that came down from the Pomeroy Hills. Its material, 

 however, is sandy, and its included stones are all washed and water-worn ; 

 it is a glacieluvial deposit " (p. 142). 



Though it is not proposed here to enter into tlie question of the mode of 

 origin of the "eskers" of the Central Plain, it may be stated that I am 

 ill full agreement with Professor Gregory in regarding the majority of these 

 ridges as marginal formational features, i.e. as moraines formed in water, 

 having taught this view in my University lectures for a number of years. 

 I submit, however, that the mounds and ridges of the moorlands of Tyrone, 

 where formed in ponded waters, differ in no respect, other, than in size, from 

 those of the Central Plain. The materials of the ridges of both regions were 

 alike dumped down in lake waters, the waters of Tyrone, however, standing 

 at a higher level than those covering the former region. 



In the cramped valleys and high-level plains of Tyrone true moraines, 

 formed above lake • level, naturally predominate, and only over the 

 relatively small part of their course where they traverse the floor of the 

 depressions are the conditions of formation identical. The Dergbrough and 

 other large moraines in the Sperrin Mountains are, over those stretches where 

 the ice stood in water, indistinguishable either in appearance or in structure 

 from the marginal " eskers " of the Central Plain. 



lu Tyrone, and in all the region examined, these waters were indubitably 

 those of fresh-water lakes, and not of the sea. Apart from the post-glacial 

 raised beach, no trace of submergence in N.-W. Ireland was anywhere 

 discovered during the course of this investigation. On the contrary, in late- 

 glacial times, as the Burngibbagh valley unmistakably proves — several other 

 cases from the north of Ireland could be readily cited — the level of the sea 

 was below the 100-foot contour line. 



An extremely fine morainic country occurs to the north of Pomeroy. 

 These moraines, sometimes very irregular and hummocky, sometimes smoother 

 in outline, were formed by an ice-push from the west, as shown by their 

 convexity towards the opposite direction, and by the granite and pyroxenic 

 erratics which they contain. These ridges, moreover, sweep in a series of 

 curves, springing out of each other tangentially, the inner curve invariably 

 on the western side of the outer. 



