part 3] GLACIATION OF NOttTH-EASTERN IRELAND. 359 



railway, and in the largest of these the following section is to be 

 seen : — 



Thickness in feet. 



Brown sands with lines of pebbles 5 



Coarse gravel containing boulders which measure up to 



3 feet in length, with lenticles of red stratified clay 20 



Pebbles of Ailsa Craig eurite are very common in the gravel, 

 which also contains masses of Carboniferous sandstone (Canister) 

 as much as 3 feet long, schist, gneiss, red quartz-porphyry, flint, 

 chalk, quartzite, quartz-breccia, red granite, and basalt. 



The whole drainage-basin of the River Tow (Bally castle River), 

 from Capecastle downwards, is deeply filled with drift, the streams 

 flowing in deep valleys excavated in and floored by it. There is also 

 deep drift all the way from Capecastle to Armoy, and there seems 

 to be little doubt that, if the glacial deposits were removed, the 

 Bush River would flow down the valley to the west of the railway, 

 and enter the sea at Ballycastle, as it probably did in pre-Glacial 

 times. 



Glacial Overflow-Channels and the Origin of the 

 Terrace-Gravels. 



The terrace-gravels of the Carey and Glenrnakeeran Rivers were 

 formed as deltas in a temporary lake, the waters of which were 

 held up by the ice-front; and the various terraces represent the 

 successive levels of its waters as the margin of the ice slowly 

 retreated northwards. 



During the maximum extension of the Scottish ice, the whole 

 of the ridge Cushleake Mountain-Crockaneel-Oghtbristacree- 

 Agangarrive Hill, separating the area under consideration from 

 Glendun which lies on the south, was completely overridden, and 

 attention is now directed to the successive stages of its emergence 

 from its ice-covering. 



It will be evident, from the drainage phenomena which will 

 shortly be described, that immediately after the masses of ice north 

 and south of this ridge had ceased to be confluent, the glacier 

 on the south (in Glen Dun) stood at a higher level than that 

 in the Carey River and Glenshesk. This can be accounted for 

 by the fact that the mouth of Glendun opening to the sea 

 at Cushendun lay centrally in the track of the great ice-sheet 

 issuing from the Firth of Clyde, and there was little to hinder 

 its advance up the glen ; while the Carey and Glenshesk area 

 lay somewhat to the right of the centre of flow, and was protected 

 to a certain extent by the great rampart of Fair Head, there being 

 also a comparatively easy escape for the Clyde ice across Rathlin 

 Island and through the channel between that island and Islay. 



Accordingly, we find that there are two overflow-channels, both 

 falling northwards, and connecting Glendun with the valleys 

 lying in that direction. The smaller of these channels is at a 

 height of slightly over 1000 feet, passes between Agangarrive Hill 



Q. J. G. S. No. 315. 2 c 



