PRESIDENTIAL ADDRESS. 549 



Undermost ; but the evidence implies that the two ice-sheets were coexistent, and 

 there is no indication of any break in the glaciation.^ Both here and in the Dublin 

 district there appears to have been a shrinkage in the AVest British lobe while the 

 Ivernian ice was still advancing, which again points to a shifting westward of 

 the area of greatest precipitation. 



Owing to its peripheral position, the Cork district seems to have been set free 

 from its ice-mantle much earlier than the more northerly parts of Ireland ; and if 

 there had been marine submergence later than the period of maximum glaciation, 

 it should have left clear traces in this area. But we found, instead, that all the 

 deposits newer than the boulder-clay were unmistakably of fluviatile or sub-aerial 

 origin, and occupied positions that they could not have maintained if any sub- 

 mergence had occurred. 



Dublin District. — In the Dublin district the lower shelly boulder-clay was 

 carried for some distance inland during an early stage in the glaciation, but after- 

 wards there was a great outpouring of the Ivernian ice from west-north- 

 west round the northern Hank of the Dublin Mountains. As the Pennine ice was 

 deflected southward on reaching the North Sea Basin, so was this Ivernian ice 

 deflected southward parallel to the coast in the Irish Sea Basin, the persistence of 

 ice-lobes within the basins being the only adequate explanation in both cases. 



The shelly gravels associated with the Dublin drifts are of peculiar interest, 

 since they occur at heights ranging up to 1,200 feet above sea-level, and are typical 

 of the other high-level shelly drifts of the ' West British ' basin, including the 

 much-discussed deposits of Moel Tryfaen and Macclesfield. The position of these 

 gravels on the flanks of the Dublin Mountains at the margin of the heavily drift- 

 covered country, their moundy outlines, spoi'adic development, disregard for 

 contours, character of the fauna, relationship to the boulder-clay, and, in fact, 

 every feature they possess, tell against the possibility of these gravels being of 

 marine origin or other than the marginal deposits of the ice-sheet. Gravels at 

 much lower levels in the same district that are associated with the ice-flow from 

 the interior of the country contain no shell fragments. 



The fine coast sections between Killiney and Bray show the usual features of a 

 lower shelly boulder-clay brought in obliquely from the seaward and an upper 

 boulder-clay derived from the landward ice ; and they show, too, that the so-called 

 * middle glacial ' gravels are merely local modifications of the glacial series, inter- 

 woven with the boulder-clays and of contemporaneous accumulation. In this 

 district there is again strong evidence that the land remained above sea-level 

 during the final waning of the ice, and that it has not since undergone any sub- 

 mergence, except to a depth of not more than 10 feet above present sea-level. 



Belfast District. — In the country around Belfast the glacial phenomena pre- 

 sented the same general features. The principal constituents were again — a 

 shelly boulder-clay, brought in from the northward, interlocked in a few places 

 with moundy gravels, also containing a few shell fragments ; and a conterhpo- 

 raneous drift in the hilly interior of more immediately local origin, associated 

 with gravels of like composition and without any marine relics. 



The only new feature was the presence of a mass of unfossiliferous sand and 

 laminated clay in the recess at the head of Belfast Lough, which appears to 

 have been deposited in a glacially dammed lake during the waning phase of the 

 glaciation. This deposit is in places iuterbedded with and partly overlain by 

 boulder-clay. Its relation to the surrounding drifts seems only explicable under 

 the supposition that the oscillating margin of the ice-lobe was continuously 

 present in the vicinity ; and nowhere in the district did we find any evidence to 

 suggest that there were epochs of glaciation separated by warm interglacial 

 episodes. 



The conditions in this district subsequent to the disappearance of the ice- 

 sheets are recorded in the post-glacial deposits at the head of Belfast Lough, 

 which have been carefully investigated by Mr. R. Lloyd Praeger.* A bed of peat, 



• Wright and Muff, op. cit., p. 272. 



* ' Report on the Estuarine Clays of the North-east of Ireland.' Proc. Roy. Irish 

 Acad. (3) vol. ii. (1892), pp. 212-289. 



