Charleswouth — Glacial Geology of North- West of Ireland. 1 8 1 



The Barnesmore Hills, uoitli of Lough Eslce, are composed chiefly of 

 granite. 



The town of Ballyshannon, at the mouth of the Eiver Erne, stands at the 

 apex of a triangular outcrop of Archaean gneissic rocks,' bordered on either 

 side by beds of Carboniferous age, and with its base to the N.E. of Lough 

 Derg. While gneisses predominate, the complex also includes granulites, 

 granites, pegmatites, schists, eclogites, and epidiorites. 



Eocks of Carboniferous age, chiefly sandstones and shales, form a strip of 

 country surrounding Donegal Bay. They also underlie the greater part of the 

 basin of the Eiver Eoe and the low-lying region of Draperstpwn, the recess in 

 the hills east of Newtownstewart, the plain drained by the Fintoua Eiver, 

 the Clogher and Erne valleys, and the plains of Monaghan and Cavan to the 

 south of Slieve Beagh. The latter is composed chiefly of " Millstone Grit." 

 Sandstones and conglomerates of O.E.S. age form the Eintona hills, separating 

 the Clogher Valley from the Fintona Plain. 



The steep face of the north-western edge of the Antrim Basalt Plateau, 

 which rests on Chalk, Lias, and Trias, overlooks Lough Foyle, while to the 

 east the surface of the plateau slopes out of the area under review towards 

 the valley of the Bann. 



Stretchhig from Omagh to Draperstowu and to the south of the Sperrin 

 Mountains is a broad, flat strip of country, designated for the purpose of this 

 paper " the Omagh-Draperstown Corridor." It is bounded on the north by a 

 great fault, running N.E.-S.W., and extends as a dreary expanse of turf and 

 moorland. On the south it is closed in by a range of hills, attaining at its north- 

 eastern end considerable altitudes, of which Oughtmore, Beleevnamore, Fir 

 Mountain, and Slieve Gallion (just outside the area of this paper) are the chief. 

 The trend of this range of hills is generally W.S. W.-E.N.E., coincident more 

 or less with the prevailing strike of the rocks. These, like the rocks of much 

 of the corridor to the north, are chiefly aplianites, schists, and gneisses, which 

 by reason of their hardness have imparted a stern and rugged character to 

 the scenery ; even where thick turf abounds, hummocks and crags of these 

 materials project above its surface. The sills and bosses of gabbro have been 

 altered to epidiorites, etc. 



Towards the western end of this flat country lies a small, roughly triangular 

 tract of Ordovician and Silurian rocks,- near the town of Pomeroy. These 



' For a description of these and their relationships, see Professor G. A. J. Cole's 

 paper, On Metamorphio Rocks in Eastern Tyrone and South Donegal, Trans. Roy. 

 Irish Acad., vol. sxxi (1900), p. 431. 



- W. G. fearnsides, The Lower Palaeozoic Rocks of Pomeroy, Proc. Roy. Irish 

 Acad., vol. xxvi B (1906-7), p. 97. 



