191213] 6 5T 



these materials must have flowed southward with a fair measure 

 of directness, else it could scarcely have borne the materials to 

 such a height on the east side of the valley. On the sea-floor it 

 would have found shells, mingled with marly clay and rounded 

 debris of the basalt, as well as splinters of chalk and chalk-flints, 

 many of which stud the Boulder-Clay. 



In the Bann Valley I have not had full opportunity of tracing 

 out the occurrence of the corresponding Boulder-Clay ; but think 

 the deposit on the ground, overlooking the Bann on the east, 

 largely consists of the red Boulder-Clay. In this valley, however, 

 a certain association of granitic, schistose and epidioritic rocks, as 

 erratics, occurs in such notable prominence that one is forced to seek 

 a cause for their presence. Such an association can scarcely have 

 originated in the south, a source of this character being wanting 

 there; there is, however, a distinct multiplication of granite 

 erratics, noticeable as one proceeds southward by Garvagh and 

 Kilrea, pointing to Slieve Gallion as the source. It would be a 

 somewhat bold conclusion to ascribe the occurrence of the schists 

 and epidiorites to the first great ice-flow, namely, that from the 

 eastward. Of an extensive movement from Donegal and London- 

 derry over the basalt plateau and other intervening high grounds, 

 there seems no evidence whatever, and no reasonable grounds for 

 conjecture. We are, therefore, shut up to the north or north-east, 

 where the sea conceals the prolongation of the Central Highland 

 rocks, and part of the Archaean Gneiss area; and I am glad to 

 find confirmation of this conclusion in that of Dr. Dwerryhouse* 

 regarding the ice-flow over this part of Ulster. 



An important corollary to the conception of this inflow from 

 the north, seems to obtain in the broken up condition of the 

 north-west face of the Benevenagh promontory. Thick ice, with 

 an erosive pressure of some 50 tons on the square foot, operating 

 upon the escarpment beneath the cliffs of basalt some 800 feet in 



*" British Association Report" for 191 1. 



