168 



Proceedings of the Royal Irish Academy. 



A ridge or mound of Eoulder-clay, whicli attains a maximum 

 height of 18 feet above present high water, runs (or ran — for much of 

 it has been long removed) north-east from the south side of the arch 

 over the railway across the site of the British Aluminium Company's 

 works (from I) to I" on plan, fig. 2). This ridge has a steep slope on 

 either side. Southwards, at the extreme point of the Curran, the 

 Boulder-clay is seen again a couple of feet above high water. In the 

 opposite direction, the ground drops to the northward; and a depres- 

 sion runs across the base of the Curran promontory from sea to sea. 

 Bay Eoad, which is level from end to end, occupies the centre of this 

 hollow. Cuttings here showed no trace of Boulder-clay down to about 

 half-tide level. It is evident, therefore, that during the period of 

 submergence in which the gravels and associated beds accumulated, 

 tliis ridge of Boulder-clay formed an island, and later a tidal bank, 

 against and finally over which the gravels were deposited. That the 

 Boulder-clay ridge was exposed to the action of the waves before it 

 got covered over with gravels was evident in one of our trial pits, 

 where its surface was found to be covered with large sub- angular 

 blocks of stone clearly derived from the attrition of the clay. On this 

 boulder-beach, the characteristic implement-bearing gravels were laid 

 down to a depth at this spot of 10 feet. The Boulder- clay bank rises 

 near its northern end (at the Aluminium Works) to 1 8 feet above present 

 high water, or only 2 feet less than the highest point of the gravels. 

 The gravels are thickest just to the leeward (southward) of this knoll ; 

 and the whole conformation of the Curran shows that the gravels 

 collected around, and as a long tail behind this Boulder-clay islet, on 

 each side of which the tides streamed up and down. 



Prior to the deposition of the gravels, fine blue Estuarine Clay was 

 laid down in the depressions, both to the north and south of this knoll. 

 The formation of this mud is not so easy to account for, requiring, as 

 it does, water free from violent currents. Perhaps we may reasonably 

 assume that at that period the gravels formed a barrier further on 

 the seaward side, and shut out the waves of the open sea, even as the 

 Curran gravels do now ; and that on further subsidence of the land, 

 the gravelly beach advanced till it covered the clay as at present. 

 Across the Bay Road depression, a broad, yellow, sandy beach-deposit 

 intervenes between the clay and the overlying gravels, facing the open 

 sea ; but on the other side of the Boulder-clay islet, fronting the 

 sheltered waters of the lough, thin beds of black sand, the product of 

 the muddy waters of the bay, overlie the clay. 



The gravels themselves vary greatly in the sections exposed, not 



