Cb AKL-ESWORTB— Glacml Geology of North-West of Ireland. 253 



The stream, forming tlie highest of these features, flowed iuto "Lake 

 Gortin-Glenelly," overflowing by the Inver Channel. Tlie others were 

 manifestly too low to escape by this channel, and pouring north, served as 

 the escape of the waters of this large lake by the Foyle valley along the 

 western side of the Sperrins. "Lake Gortin-Glenelly," just prior to the 

 abandonment of the Inver Channel and the- initiation of the lower 

 Meenawaddy channels, was of great size ; its surface area was some 33 sq. 

 miles, its greatest length about 13 miles, its greatest depth over 300 feet. 



The ice, wliich swung across the western end of the huge amphitheatre, 

 from Mary Gray to the hill east of Meenawaddy and the western flanks of 

 Meenashesk, formed a diminutive lake at Contheni Hill ; the shallow channel 

 (C.H.), intaking at about 800 feet, OD., was its outlet. This channel entered 

 a larger lake impounded in the recess to the S.E. of Strabane, which was 

 drained northwards by the Foul Glen (F.G., E. of Knockavoe). This glen 

 intakes at 725 feet, O.D. 



A large lake was held up in the valley of the Glemnornan Eiver, IST.E. of 

 Strabane. At an early stage these waters were confluent with those of the 

 larger " Lake Dunnamanagh." ^ With the recession of the ice, this lake 

 divided into two, the one in the Dunnamanagh valley, the other in the 

 Glenmornan valley.^ This lake was drained by the channel, falling gently 

 north, and intaking N. of Gorticum Irish. The great terraces in the Glen- 

 mornan valley, the altitude of which is about 400 feet, O.D., or slightly 

 higher, were formed at this stage, very largely by material swept out of the 

 ice. An earlier position of the ice-front is indicated by the small, yet 

 extremely good, "in and oat" channel falling north, carved out of the 

 hillside just E. of the Gorticum overflow. 



Later reti'eat nncovered the col north of Windy Hill, and initiated the 

 magnificent valley (W.H.) carved along this line. It intakes at 381 feet, CD., 

 and falls east.' 



This stream formed a very fine deltaic terrace, where, at Crockanore, it 

 entei-ed " Lake Dunnamanagh." By subsequent down-cutting in late-glacial 

 times most of this high terrace was removed. 



'An earlier stage is I'epresented by the deep glen excavated in "solid," runnino' 

 northward along the eastern side of the Dunnyboe valley. It was formed when the ice 

 still stood in the latter, and is clearly an exact analogue of the " Balix channel " on the 

 side of the Inver valley. 



2 The deep glen, cut in " solid," falling west into the Glentornan valley from its head 

 clearly carried a large stream, draining from the Dunnyboe Glen. Its waters would 

 seem to have escaped on to or into the ice. 



^ Tlie shallow valley, about three-quarters of a mile S. of this, falling east into the 

 Gorticum overflow, probably acted as a gutter carrying oft' the waters flowing directly 

 from the ice-face. 



E.I. A. tUOC, VOL. XXXVI, SECT. B, [2 G'\ 



