Charlesworth — Glacial Geology of North- West of Ireland. 279 



along the stretch between Moville and Inishowen Head may mark earlier 

 stages.' 



The morainic mounds about half a mile S.-E. of Magheralahan and 

 those just south of Moville were thrown down along the western edge of the 

 Foyle Glacier. 



Still later phases of the retreat are represented by the valleys of 

 accumulation and denudation west and south-west of Muff.^ Hei'e the 

 streams and ridges exhibit a striking parallelism, due to the swinging of the 

 ice out of the " Pennyburn depression " into the Foyle estuary. To the 

 north of Muff the northward deflection of the streams is readily recognisable. 

 Though these valleys are largely due to ridging of the drift, one or two were 

 undoubtedly scoured out by marginal drainage.' 



It is difficult to correlate the marginal phenomena on the west and east 

 sides of the Foyle estuary. It may be said, however, that the "Ballyrattan " 

 and " The Colonies " channels were most probably in action at some period 

 during the existence of "Lake Claudy " and the operation of the " Feeny " 

 and "Ballymoney" overflows, and were probably somewhat later than the 

 third stage of the Sperrins retreat. 



The ice, which retreated off the eastern shoulders of Slieve Snaght and the 

 western slopes of the range bounding Inishowen on the east, formed a large 

 Glentogher glacier ;^ this gradually shrank southwards, to form, finally, merely 

 a small lobe protruded from the edge of the larger Foyle Glacier. 



The extensive deposit which stretches from Carndonagh northward to 

 Doon Bridge" represents the deltaic fan thrown down by the great river 



• Like all the glacial marginal channels of this strip, these are parallel with the grain 

 of the country. It is in consequence a matter of some difficulty, if glaciated surfaces be 

 absent, to distinguish between those depressions produced by differential ice erosion and 

 those subsequently modified by marginal drainage. The valleys just described are 

 undoubted "dry" valleys; of the marginal origin of the rest I am very doubtful. 

 Equally uncertain are the two steps, the one occurring at 280 feet, O.D., the other just 

 below, in the steep face of Binion, on the western side of the peninsula; these are more 

 probably structural features. 



- The morainic character of tlie deposits is noticeable in the sands and gravels of the 

 Galliagh Burii and in the vicinity of the Old Race Course, where the material, as 

 exposed in the sections (25 feet high), is seen to be the product of the Donegal glaciation, 

 and to include much Barnesmore granite. 



^ E.g., the valley east of Thompson's Town Bridge and that at Soppog, at the head of 

 the stream flowing to Muft'. Of the valley east of Ballyarnet I am less certain. 



* Though the exceedingly deep and steep-sided gorge of the River Straid is doubtless, 

 in the main, a rejuvenation feature, it ijossibly carried ofi' the drainage of a lake held up 

 by the ice-front which swung across from the hill of Crocknakilladerry to the hills running 

 from the N.-E. slopes of Slieve Snaght. 



''This great deposit of water-worn material is revealed in several places, e.g. at Doon 

 Bridge, and wherever the sea has eaten into it ; also in the large excavation used as 



