igiS. HiNCH. — The Irish Sea Glacier. 59 



Sea ice is that where it is found in contact with the boulder- 

 clay of the ice-sheet from the centre of Ireland, the marly 

 boulder-clay is always overlaid by the boulder-clay of the 

 ice from central Ireland. The significance of this fact will 

 be seen later when the relative ages of the individual ice- 

 sheets come to be discussed.^ 



Having traced the development of the Irish Sea Glacier, 

 with its varying deposits, we now turn to some of the 

 problems connected with its decay. For practically half a 

 century glacial geology in the British Isles was dominated 

 by the theory that at least one interglacial period had 

 occurred and that during this interglacial period these 

 islands had been submerged to at least the upper level of the 

 shelly drift, that is to say, the upland glacial deposits of the 

 Irish and Welsh hills marked the shore-hnes of the inter- 

 glacial sea ; and that the eskers in the plain were sand- 

 banks created by the curreiits of the same sea. Let us 

 recall some of the opinions put forward by those holding 

 this view. Thus we have Prof. Hull, the Director of the 

 Geological Survey of Ireland for many years : — " As its 

 name imports, it [i.e., the Middle Sand and Gravel] consists 

 of stratified sand and of water-worn pebbles, sometimes of 

 large size ; and, as it contains marine shells in various 

 places, may be regarded as a formation of marine origin, 

 which has been strewn over the bed of a comparatively 

 , shallow sea." ..." These facts lead us to infer a great 

 general depression of the land extending over the northern 

 portion of the British Isles . . . and . . . assuming the greatest 

 depression to have reached 1,500 feet below the existing 

 level, the Irish area must have presented the appearance 

 of an archipelago of islands." -And further, we have Mr. T. 

 Mellard Reade when writing of " The high and low-level 

 shelly, drifts around Dublin and Bray": — " P^ story is 

 nothing without a moral, and a geological paper without 

 conclusions. . . . The phenomena . . . appear to me to lend 

 no support to the Irish Sea Glacier hypothesis. . . . The 



^ Geol. Survey Mem., Geology of Cork, p. 106 (1905). 



2E. Hull, " Physical Geology of Ireland," pp. 112-116 {1891). 



