Charleswoeth — (xlacial (Geology of North- West of Ireland. 24 1 



at tlie outfall of the Altnasheskin ovevliow (A.S.). Sections, some 60 feet 

 or more in height, in the sides of the White Burn, show great quantities of 

 sand, in places finely current-bedded ; their arrangement clearly indicates 

 stream deposition from the south. 'J'he material is composed chiefly of well-worn 

 disc-shaped pebbles of schist, derived from the sides of the Altnasheskin glen. 



The huge lake, extending far up the valley of theBenady Glen, received a 

 stream of no great size, flowing northwards over the Glenshane Pass. The 

 recess to the south of the latter is extremely small, and the overflow corre- 

 spondingly diminutive. The channel (G.P.) intakes roughly about 975 feet, 

 O.D., but fails to indent the 800-foot contour. 



Where did the waters of this great " Lake Benady " escape? In the great 

 basalt escarpment, Benbradagh (1,535), Donald's Hill (1,318), Keady Hill 

 (1,101), and Benevenagh (1,260) are from south to north the most conspicuous 

 features. The altitudes of the intervening cols are 785, 740, and 740 feet, O.D., 

 respectively taken in the same direction. On the col, some four miles south- 

 east of Benevenagh, in the most northerly recess of all, is a small overflow, 

 the "iVIurder Hole" of the one-inch O.S. map. This valley intakes at 

 roughly 750 feet, O.D., and falls gently east. It i.s cut in basalt to a depth of 

 some 30 feet. ISTot only is the intake of this valley some 40 or 50 feet 

 lower than the level of " Lake Benady," as given so accurately by the 

 Mvirnee Hill terrace, but in comparison with the Altnasheskin glen (A.S.),- 

 only one of the feeders of this large lake, the " Murder Hole " is quite 

 insignificant and totally inadequate to carry off all the drainage from 

 the ice-free parts of the Sperrin Mountains and the flood waters from 

 the melting ice-front, all of which, as the map (PI. VIII) clearly shows, 

 must have been discharged by the outlet of " Lake Benady." With the 

 single exception of this small overflow, the cols just mentioned show no 

 trace of drainage across them, from west to east. It would seem that the 

 lake waters were discharged over the ice or, more probably, by a channel or 

 shelf along the face of Benbradagh, but now completely effaced by the later 

 slips. This channel probably drained into a lake held up against the escarp- 

 ment of the basalt plateau ; its outlet, now no longer recognisable, was cut 

 along the face of Benevenagh. 



This lake received the surplus waters of lakes impounded on the dip slope 

 of the plateau by ice standing in the Bann valley. These streams, discharging 

 from east to west, produced the two pots, the " Legananam Pot " and the 

 " Legavannam Pot," both in the recess to the north of Benbradagh.' 



The extremely fine sand, exposed in the banks of the Benady river above 



' They cut the 600 and 700 contdur.s. 



