Charlesworth — Glacial Geology of North- West of Ireland. 269 



that ice which was sufficiently powerful to press over the summit of Slieve 

 Gallion and down the valley of the Bann in the one direction, and over the 

 Fintona and Slieve Beagh hills in the other, must have thrust greatly to the 

 south, over the comparatively low country extending to the south-east of 

 Pomei'oy and over the plains of Tyrone. 



The ice, retreating northward from the Slieve Beagh Hills, lingered longer 

 in the larger valleys than on their intermediate watersheds. Thus, the series 

 of moraineSj spanning the large Donaghmore Glen, indicates its occupation by 

 a lobe of ice at a time when the bounding hills were ice-free. These morainic 

 features mark the successive phases in the withdrawal of the glacier along 

 the depression to the wide plain to the north. The lake so impounded 

 drained by the large valley which, beginning at about 790 feet, O.D., falls 

 S.-E. towards Eosslea. 



1'he ice protruded in similar fashion into the large depression of Glennoo. 

 Its behaviour here is likewise demonstrated by the morainic mounds and 

 ridges sweeping down into the valley from the sides. Until escape by 

 channels along the north-western liank of Slieve Beagh was rendered possible 

 by a still farther retreat, the lake held up by this lobe of ice discharged its 

 waters by the large valley at the head of the recess. This channel, intaking 

 at over 700 feet, O.D., falls rapidly to the S.-S.-E. 



In retreating off Slieve Beagh itself, a small extra-morainic lake was 

 held up in the valley on its north-west flank. The surplus waters, during an 

 early phase, were carried off by a small valley, intaking at about 900 feet, 

 O.D. This outlet had been in operation for only a short period when it was 

 superseded by a great and deep, steep-sided gash running along the western 

 face of the mountain.^ It commences at about 650 feet, O.D. The large valley 

 to the west of this, also excavated in rock, likewise acted for some time as a 

 marginal channel, though it served also as the natural drainage outlet for the 

 ice-free area surrounding the higher part of the valley. The large glen west 

 of this again (E. of hill 608), though acting as a marginal channel carrying 

 off the waters from the ice-face which rose from its western side, served 

 chiefly as the outlet for the surplus waters of the extensive lake held up in 

 the valley of the Glennoo. The intake is about 590 feet, O.D. "Lake Glennoo " 

 was later drained by the "Orocknagrally channel" (between hills 608 and 684), 

 which intakes at about 550 feet, O.D. This channel continued to discharge 

 the waters of the impounded lake, while the ice wheeled northwards to 

 assume the position indicated by the morainic ridges running roughly 

 E.-W. from hill 684. By the freeing of the lower northern slopes of Black 



1 This great trench is readily recognizable at Fivemiletown, some four miles away. 



R.I. A. EKOC, VOL. XXXVI, SECT. B. [2 H] 



