Gharlesworth — Glacial Geology of JS^orth-West of Ireland. 239 



as finally evaeua.ted, are of gi-eat size and doubtless originated in one or two 

 cases ^ as the relatively small channels produced by the waters draining 

 directly off the ice- front as the ice parted to the north and south of the 

 watershed. All these direct channels fall north, and indicate that the ice 

 withdrew more rapidly on that side than on the south of the waterslied. 

 Hence, in the case of the " Lake Cloghornagh," its level was so lowered by 

 the opening of lower cols across the northern tributary spurs that the smaller 

 lake, held up in the recess of the Oughtnamwella and Glenirn burns, drained 

 northwards across the col. This " Cloghornagh" overflow (O.C.)- is deep, and 

 carved out of schist. The intake is about 1,090 feet, O.D.' 



In these independent lakes, held up in the recesses south of the main 

 watershed, the waters stood at different levels, the height of each lake being 

 determined by the altitude of the col at the head of the valley across which the 

 outlet was cut. Hence, the highest lake was that which drained by the channel 

 across the ridge S.-E. of MuUaghaneany (2,070), the intake of which was roughly 

 1,350 feet, O.D. The " Tamnagh " channel (T.) starts on the col to the N.-W. 

 of Dart Mountain (2,040) and intakes at 1,420 feet, O.D. The intake of the. 

 channel across the col E. of Mullaghclogher (1,896) is roughly 1,350 feet, O.D. 

 One of the most easterly of this series of lakes was impounded in the upper 

 part of the large valley of the Glengomna Water, and discharged its waters 

 by a fine valley falling east (intake just below 1,250 feet, O.D.) into "Lake 

 Altalacky." ISTo trace of connecting streams across the intervening subsidiary 

 watersheds was observed. The sands and gravels observed in all these 

 recesses up to about 1,200 feet, O.D., are doubtless the lacustrine and moraine 

 deposits of these lakes. These direct overflows were not thrown out of action 

 until the ice-front had shrunk southwards and well away from the main 

 watershed, and the great valley of the Glenelly had become ice-free. As the 

 ice swung off the hills, the lakes from east to west became in turn confluent 

 with the waters of " Lake Glenelly." 



Held up in the recess to the north-west of Draperstown was a lake — " Lake 

 Altalacky" — some 700 feet deep in its deepest part near the ice-foot, and of over 

 six square miles surface area. The outlet at the head of this great recess 

 might be expected to bear some relationship to the size of the lake whose 

 surplus waters it discharged. This overflow is the Altnahegiish valley (A.O.), 

 the finest of these direct channels. Its intake is just above 1,000 feet, 

 O.D. The valley is quite good on the col, and carved out of schist ; it falls 



' E.g., that between Dart Mountain (2,040) and Learmount Mountain (1,615). 

 - The letters in brackets correspond to similar letters on the accompanying maps, and 

 are inserted as aids to identification. 



' The lake was continuous across the col at the head of the Aughtnamwella Bui-n. 



