292 Proceedings of the Royal Irish Academy. 



the ice receded out of the Elatagh glen, for not until the lobe thrust into this 

 depression had completely withdrawn to the valley of the Finn — a distance 

 exceeding three miles — was a lower outlet possible.' 



A similar lobe impounded a lake in the recess of the Sruhanpollandoo, 

 which drained by a broad valley W. of Binswilly — the " Owenbeg channel " 

 (0.) ; it intakes below 700 feet, O.D. This position of the ice-front probably 

 coincides with the Finn moraine west of Lough Finn. A later position is 

 represented by the broad channel (S.) falling S.-W. into the valley of the 

 Scallan Eiver and intaking at about 590 feet, O.D. This served as the 

 outlet of a large lake held up in the Cummirk valley. 



With progressive recession of the ice and by the opening of lower cols, 

 the level of " Lake Deele " was gradually lowered. One of its drainage 

 channels occurs west of the hill 781 (D.C.) ; it intakes at 570 feet, O.D., and 

 falls north into the Dooballagh Burn and the valley of the Swilly. The last, 

 lowest and largest is the very broad and flat-floored valley (C.),' which 

 intakes about two miles JST.-N.-W. of Convoy at about 370 feet, O.D., and 

 falls northwards into the Swilly valley. 



" Lake Deele," at the stage represented by this " dry " valley, received 

 a feeder flowing via the depression situated east of Liskeran (].■.) and two 

 or three miles N.-N.-W. of Stranorlar. 



It is difficult to correlate the phases of the retreat of the ice in this area 

 with those positions marked by the marginal drainage along the western foot 

 of the Sperrin Mountains already recorded. The ice position given by 

 the two channels just described may, with some probability, be correlated 

 with that indicated by the " Strabane Glen," when the great ice-lobe 

 terminated somewliere in the neighbourhood of Broomfield. 



The moraines at Clady and those on the northern slopes of the Finn valley, 

 east of Iji.scooly, and in the bottom of the valley near Castlefinn, mark later 

 stages of the retreat of the " Great Finn Glacier." 



Still further withdrawal caused the disintegration of this glacier into the 

 separate streams feeding it, chiefly those issuing along the Eeelan and 

 Daurnett valleys from the Barnesmore Hills. The morainic ridge east of 

 Cloghan Station was formed by the Eeelan Glacier just before its withdrawal 



' Therefoi-e, both during the maximvira and late-glacial phases, the direction of ice- 

 motion was towards the N.-E. Yet on the Geological Survey Map (Sheet 16), an arrow 

 is engraved indicating ice movement to the S.-W. in the Elatagh valley. A similar error 

 was noted in Mulroy Bay ; an arrow on the Geological Survey Map denotes ice pro- 

 ceeding southwards in the southern part of the bay, though from all the evidence it is 

 abundantly clear that no ice flowed from the sea ly; the fiord. 



2 This valley, south of Glenniaqiiin Station, is traversed for roughly two miles by the 

 Stiabane and Letterkenny E,ailway. 



