248 Proceedings of the Royal Irish Academy. 



Glenellj." Its outlet was over the col at its head (just over 700 feet) 

 and into the valley ot the Dimnyboe Eiuii. 



The waters of this lake and of " lake Gleiielly " flowed northward through 

 their respective overflow channels into the lake held up in the valley extending 

 southwards from the village of Dunnaroanagh, foi-ming gi-eat deltaic terraces 

 where they entei-ed the lake.^ The altitude of these higher terraces corre- 

 sponds closely with the intake of the highest overflow channel to the south- 

 east of Lough Ash (LA.). This extremely large valley intakes at about 580 

 feet, O.D., is entirely excavated in rock, and falls east. Smaller channels 

 coming into this " Lough Ash " overflow from the west probably represent 

 the erosion by the flood waters pouring along the valley in which lies Lough 

 Ash itself and fiom the ice-front standing near the entrance to the valley.* 



The two small and shallow vaileys. south of JBaUynacross, possibly repre- 

 sent slightly earlier phases in the retreat from the Mullaghanimma lulls. 



A small lake, held up in the valley south of Liseloon, diaiued southwards 

 by a channel (L.O.) into the '■ I^ugh Ash " overflow, the combined waters 

 flowing along the upper part of the Gleurandal Eiver into " Lake Claudy." 

 A slightly earlier stage is represented by the two valleys falling east to the 

 south of Slieveboy. The more southerly valley is slightly lower at the intake 

 than its neighbour, and as pc^t-glacial erosion of either valley is clearly 

 n^bgible, a slight re-advance of the ice-margin with renewed cutting of the 

 southern valley would seem to have taken place. This advance probably did 

 not exceed one-quarter of a mile. 



A lake of considerable size was dammed up by the ice, which stood across 

 the valley of the Fanghan, just west of Claudy, and swung from the northern 

 slopes of Eglish Hill on to the western shoulder of Boultybracken. The ice- 

 front stood about the site of Oak Lodge, for the mounds and ridges of this 

 place, described in the " LondondeiTy Memoir," p. 78, as " typical eskers with 

 steep bedding and sinuous outlines," probably represent the mateiial thrown 

 down by the ice standing in the lake waters. This lake possessed three chief 

 branches : the first extending south-east up the vaUey of the Faughau as far 

 as Learmount and Park, the second east towards Feeny, the third along the 



' E.g., above Aghabiack, and at Bunbouiiiff in the valley of the Inver Bnm, and at 

 Altishahane and near the confluence of the Dnnnyboe Bnm and Inver Bnm. These 

 teiraces are flat-topped and their composition and stractnre are revealed in nameroos 

 stream sections. In these the material is seen to consist of water-worn pebbles and 

 corrent-bedded sands in great quantities. 



- The deltaic and morainic mounds impounding the waters of Lough Ash m:irk its 

 position. Sections in these mounds show strongly corrent-bedded and water-worn sands 

 and gravels, consisting chiefly of flat discs of schist, with mnch sand derived from the 

 disintegration of quartzose schists. 



