Chakleswoui'H — Glacial Geology of North- West of Ireland. 281 



of the Owenerk, and which drained by the valley falling northward along the 

 western foot of Eulbin.' 



Of the manner of the withdrawal of the ice from east Fanad, and of the 

 successive positions of the western margin of the Swilly Glacier during the 

 retreat, no sign was detected north of RathmuUan. On the hill-slopes west 

 of this village, however, unmistakable indications of the recession of the ice 

 were ohtained. 



A lake was formed in the broad depression of the Glenalla River, which 

 discharged by a large glen, intaking just above 400 feet, O.D. (it contains 

 , Gort Lough). A slightly earlier position of the ice-front is given by the 

 valley, about half a mile north of this lake ; a later, by the " in and out " 

 channel, above the 300-foot level, and about half a mile N.-W. of Eay 

 Wood. 



No further trace of the Swilly Glacier was noted between this locality 

 and Manorounningham. Intaking some three miles east of this village, and just 

 above 200 feet, O.D., is a magnificent overflow valley," some three or four miles 

 in length, which discharged the surplus waters of an extensive lake, held up by 

 an ice-barrier curving from the hill just north of Manorounningham to the 

 hills south-west of Pluck. The moundy sands and gravels, which cover all 

 the floor of the wide depression south-east of Manorounningham, e.g. at 

 ■Ballyboe and Monclink,^ represent deposits swept into the lake from the 

 -melting ice, A moraine corresponding to this position of the ice was observed 

 along the southern slopes of the hills about Oakmore ; a later one runs as 

 an irregular ridge from east of Letterkenny towards the river. The valley 

 soith-east of Crocknear (two miles S. of Letterkenny), which falls north, 

 appears to have been modified by marginal drainage.* Above Letterkenny, 

 all trace of the glacier was lost. 



The signs of retreat being so meagre, it is impossible to correlate the 

 positions of the east and west margin of the Swilly Glacier, or to trace in 

 more detail its mode of retreat. 



7. Tlie Mulroy, Sheephaven and Glcnna Glaciers. 



The ice which shrank off the northern peninsulas formed a number of 

 separate glaciers of which but occasional glimpses are obtained. The 



' Some waters may have escaped by the Gap of Mamore at an earlier stage when the 

 lower outlet was still uncovered. 



2 It i.s traversed by the Londonderry and Lough Swilly Railway between Manor-anfl 

 Newtown Cunnmgham. 



3 See Geol- Surv. Mem., Sheet 17, p. 28. 



^A later marginal channel is possibly represented by the poor valley occurring on 

 the western slope of this hill, above the 200-foot level. 



