312 Proceedings of the Royal Irish Academy. 



by lai-ge overflows into the Movola Elver, those on the northern side into the 

 Eiver Eoe ; these two systems of drainage were at this stage quit« distinct. 

 (Stage 2, PL Vn I.) 



"With coutinned recession, the lakes on the southern side, e.g., "Lake 

 Gortin" and "I^ake Gleneily," drained by a large transverse valley — the 

 • Inver Channel" — into similar lakes impounded on the northern side, e.g., 

 those filling the valleys of the Bumtollet and Faughan. This gi-eat 

 connecting channel continued in operation diu-ing the whole of the remain- 

 ing phases of the retreat from the Sperrin Mountains, so that all the 

 drainage from the ice-free area on the north and south side of these hills 

 and the melt waters from some forty to fifty miles of ice-front were 

 carried into the Foyle estuary by the large valleys of Gortnessy and 

 Burngibbagh. (Stages 3 and 4, PI. VIII.) 



Tbe progressive recession of the ice along the country south of the Sperrin 

 Mountains is displayed by the magnificent series of moraineswhich swing across 

 the plains of Tyrone. The ice, spread over the countiy to the east, withdrew 

 in the main behind the Beleevnamore Eange and along the " Omagh-Drapers- 

 town Corridor " ; the morainic ridges and mounds formed along the ends of 

 the lobes, thrust thi-ough gaps in the Beleevnamore Eange, are exceptionally 

 well developed (PI. IX). 



Tlie retreat from the southern region is marked by a succession of great 

 morainic belts with outwasli fans of gravel, the finest forming the tract of 

 billowy country extending from Cookstowu to Donaghmore and the south- 

 west. 



The ice withdrew northward ofitheSlieveBeagh hills, depositing moraines 

 and impounding the drainage, its surplus waters escaping by a number of 

 very fine valleys falling generally eastward or north-eastward. It retreated 

 in a north-westerly direction to the Fintona lulls, maintainir.g a bold, curving 

 front, swinging obliquely along the Clogher valley, and throwing down its 

 material as broad morainic belts. A series of very fine moraines marks tbe 

 recession of the ice behind the Brougher Mountain Eange of Fermanagh, 

 while the mode of retreat ofi' the Fintona hills is brought out by magnificent 

 morainic mounds and ridges and marginal drainage phenomena. The most 

 important overflow channel of this series traverses the range, south of 

 Seskinore : it carried the whole of the drainage from many miles of the melting 

 ice-front and from the ice-free hills stretching away to the east as far almost 

 as Pomeroy. 



The manner of the retreat of the ice along the Fintona Plain is shown by 

 the morainic ridges spanning the depression, while similar features mark the 

 successive halts in the recession of the Drumquin glacier. 



