Charleswoeth — Glacial Geology of North- West of Ireland. 



286 



Glacier." Of the retreafc of the latter, several very clear records still remain- 

 The earliest and finest memorial is the magnificent lateral moraine, which 

 forms a chain of irregular hillocks skirting the hill at an altitude of about 400 

 to 500 feet, O.D., opposite Gweedore and on the south side of the Claudy 

 Eiver.i Corresponding with this large feature is the low terminal moraine 

 which runs south from the Claudy Eiver and spans the mouth of the valley 

 (about three-quarters of a mile W. of Gweedore) where the great glacier 

 debouched upon the open country. The smallness of this ridge as compai'ed 

 with the lateral moraine is doubtless to be explained by the destruction of 

 morainic material by the powerful streams which issued from the snout 

 of the glacier. 



At a slightly earlier stage some water flowed along the valley which runs 

 east of the hill of Cregmore, on the north side of the valley. The " Cung," 

 separating Dunlewy Lough from Lough Naeung Upper, is, as E. Hull 

 pointed out, a moraine marking the position of a second pause in the 

 retreat of the Dunlewy Glacier. It is probably to be correlated with the 

 upper moraine in Glenveagh, while the lateral and terminal moraines at 

 Gweedore are of the same age as the terminal moraine at Glenveagh Bridge. 

 If this correlation be correct, almost exactly the same rate of recession would 

 appear to have characterized the glaciers in the two valleys. 



Of the southward recession of the ice along the Eosses to Gweebarra Bay 

 but few indications were observed. Many of the straight joint valleys, 

 dissecting this plain and bearing west of north, must have carried the waters 

 streaming from the southward receding ice-front. The recognition of those 

 which were so employed is a matter of great difficulty, and having but little 

 confidence in the results obtained, I refrain from mention of them. 



The large accumulation of granitic blocks, at the western foot of the hill 

 of Crockator, most probably represents the lateral moraine of the ice which 

 proceeded northward along the Eosses, and which, farther north, deposited 

 the enormous numbers of large cuboidal blocks of granite, weighing tens of 

 tons, which lie scattered over the country where the granite hills fall steeply 

 to the plain. A stream of considerable size, issuing from the edge of the 

 ice, flowed along the large valley which contains Lough Keel and falls 

 northward to Crolly. 



The small sand and gravel morahies encircling Lough Nasnahida, west 

 of Doochary, were laid down along the front of a small ice-lobe thrust into 

 the depression north of Croaghlecounell. 



The retreat of the ice from the great Gweebarra depression carried the 



' L. Aleen is held up by this moraine. 



PKOC. R.I. A., VOL. XXXVI, SECT. B. [2 J] 



