152 



Proceedings of the Roi/al Irinh. Aaalony. 



least 30 feet higher than at present. The persistence of this com- 

 paratively high land-level also accounts for the apparent gap between 

 the Bonlder-clay and the oldest post-Glacial deposit (usually peat) 

 on which geologists in England, Scotland, and Ireland have com- 

 mented. The sudden transition from beds showing Glacial conditions, 

 to others witnessing a temperate climate, represents a long- enduring 

 land-surface, and a wearing down of the Boulder-clay. Our local 

 post-Glacial history then begins with a long period of emergence, 

 and a land-level at least 30 feet higher than at present. 



Post- Glacial Sistonj. 



If we combine the information obtainable from the Larne raised 

 beach with that revealed by a study of the Belfast sections, we may 

 piece together a tolerably complete history of the post-Glacial fluctua- 

 tions of land-level in the Belfast district. Larne lies 18 miles x^.i^.E. 

 of Belfast. There is evidence that the final movement of emergence, 

 at all events, increased northward, the east coast of Ireland being 

 raised, so to speak, on a lever of which the fulcrum lay somewhere 

 south of Dublin.^ Is'evertheless, the differential movement between 

 Belfast and Larne must, if any, have been slight, and for purposes of 

 general illustration may be neglected. 



The Larne and Alexandra Dock sections, placed side by side and 

 adjusted with respect to present sea-level, stand as shown in fig. 1. 

 Leaving out of account any possible slight differential movement, we 

 may slide these sections up or down together with reference to sea- 

 level, and see how far they help us to unravel the history of the 

 deposits. An emergence sufficient to bring the Belfast peat-bed above 

 tide-level will raise the Boulder-clay on which the Larne section sub- 

 sequently accumulated far above the sea — 20 feet or more. jS'o doubt, 

 while the woods or copses which prevailed at Belfast were flourishing, 

 the Boulder-clay at Larne was being eroded into the very undulating 

 surface which it now exhibits under the raised-beach gravels. The 

 sand, Lower or shallow-water Estuarine Clay, and Upper or deep- 

 water Estuarine Clay, which, to a depth of 14 feet in all, cover the 

 peat at Belfast, give evidence of a great and more or less continuous 

 depression of the land, amounting to at least 60 feet below the level 



^ Edward Hull has devoted a short paper to this point : "On the Raised Beach 

 of the North-east of Ireland," Brit. Assoc. Eeport for 1872, Sections, pp. 113-114. 

 1873. 



