6 5 8 



[Proc. 



GLACIAL FLOOD-DEPOSITS. 



The last stages of the melting and vanishing of glaciers from 

 our region are marked by the formation of extensive deposits of 

 sand, gravel, and shingle, and of warp-clays, the former pre- 

 dominating in the Roe Valley, and the latter in — so far as my 

 experience goes — the valley of the Bann. 



The gravelly deposits in the Roe Valley are the continuation 

 of those described in the " Memoir of the Londonderry District," 

 occupying a wide-spreading flat margining the coast, from the 

 Foyle eastward to the Roe. The " Kettleholes," which form so 

 striking a characteristic of the deposit near Derry, are represented 

 also near Limavady, as may be seen beside the main road going 

 westward towards the city. 



Dovetailing with the sand and gravel, is a thick deposit of 

 highly calcareous clay, which is laid open in the important brick- 

 field at Derrymore, about two miles east by north of Limavady. 

 This deposit extends north-westward, margined by the gravels on 

 the west, and by Boulder-Clay on the east, for some two miles, 

 beyond Aghanloo. 



Similar calcareous brick-clays occur in the Bann Valley. An 

 important pit may be seen half a mile west of the Coleraine Model 

 School, just over the crest of the rising ground. It stands about 

 150 feet above datum ; and here a striking section is laid open in 

 an artificial water cut, several yards in length, showing alternating 

 beds of clay, sand, and gravel, set on end. From this we may 

 infer their original deposition against thick ice, which once 

 probably filled the extensive hollow to the westward, its melting 

 giving occasion to the great disturbance of the originally horizontal 

 beds of clay, etc., as mentioned. In the Aghadowey River, at 

 about 100 feet above datum, fine laminated calcareous clays are 

 set at a high angle, which is to be accounted for in a similar way. 



In Glejikeen, near Aghadowey, at about the 60 feet contour, 

 the brick-clay is also worked ; and, in the large pit south of the 



