Chaijlesworth — Glacial Geology oj North-West of Ireland. 251 



Gap intake and the highest terrace south of Gortin, but adjusted itself to 

 the .new level of the lake. This furtlier downcutting has resulted in the 

 formation of the deep winding valley which is cut in the "solid" and falls 

 very steeply to the new lake level. Tlie luige deltaic terrace of current- 

 bedded sands south of Gortin, exposed in the sides of Gortin Gap, and 

 possessing a flat upper surface roughly coincident with the 600-foot 

 contour, belongs to this stage. A distinct ledge along the front of the 

 800-foot terrace marks the inner edge of the lower feature. ■ 



The waters of "Lake CuUion " were lowered by the opening of a lower col ; 

 this outlet is the deep "Glengink overflow" (G.), which intakes at about 720 

 feet.O.D. This stream also formed a flat- topped terrace in the lake to the north, 

 at an altitude of about 600 feet, O.D., e.g. at Woodbrook. The hummocky strip 

 of country running from Aghalane, south of Ballynatubbrit, to Esker Bridge 

 and Kingarrow, marks the position of the ice-margin in the Culliou recess at 

 this stage. The stratified sands and gravels revealed in the sections in the 

 Cappagh Burn are, without doubt, partly lacustrine, partly morainic in origin. 



A short halt in the recession of the ice from the Cullion embayment is 

 represented by the " Killymore " overflow, E. of Mary Gray. Its intake is 

 about 660 feet, D. Deltaic deposits are poorly developed at its exit at 

 about 600 feet, O.D. 



The position of the edge of the ice on the south and the south-east slopes 

 of Mullaghcarn is given by two channels. The first of these is a very small 

 valley, intaking at an altitude of 800 feet, O.D., and draining a small lake 

 held up in the valley of the Gleneurry Burn. It falls south for a very short 

 distance, and probably drained along the edge of the ice into the second valley 

 situated N. of Mountfield. This intakes at about 780 feet, O.D., and drained 

 into " Lake Gortin." The ice-front further to the N.-E. possibly coincided 

 with the morainic strip of country running to Cashel Bridge and with the 

 morainic mounds sweeping along the hillside between Crockanboy and Slieve- 

 menagh and across the " Omagh-Draperstown corridor." 



The western limit of " Lake Gortin-Glenelly " was at one stage marked by 

 the gigantic morainic ridge of sand and gravel stretching right across the 

 Glenolly at Dergbrough, below Plumb Bridge. As traced southwards, this 

 feature dies down and over a stretch seems to disappear, but re-appears on 

 the lower flanks' of the hills and in the valley of the Owenkillevv Eiver, near 

 Spring Hill. Still farther south it is continued on the lower flanks of the 

 hills bounding this great amphitheatre on its southern side. At Levercaw 

 there occurs a hummocky belt of country, partly deltaic and partly morainic, 

 which runs generally parallel with the side of the range at an altitude of about 

 500 feet, O.D. The deposits near the exit of the Glengink overflow had a similar 



