156 



Proceedint/s of the Poijdl Irhli Acadony. 



of no other interi)retation. Even the Ballyholme beach stands higher 

 than it should if correlated with the 10- to 15-foot shelf whicli is well 

 marked in the district.^ Elevation setting in, the land rose from the 

 waves, till slightly higher than at present — probably about 5 feet 

 above its present level. A slight movement of submergence in recent 

 times has left the surface as we now find it. 



It may be worth recurring for a moment to the question of the 

 maximum submergence, since, as we have said, the shelf which is found 

 around Belfast Lough, for instance, appears to point to a less amount 

 of depression than is suggested by a study of the Belfast clays and 

 Larne gravels — namely, to about 15 feet below present levels, in lieu of 

 25 feet. From 5 to 10 fathoms is the depth of water for which, on 

 faunistic grounds, local geologists have stipulated for the Upper 

 Estuarine Clay at Belfast. In the diagram (fig. 1, Plate V), we have 

 taken a minimum, and allowed a depth of 6 fathoms (or 24 feet below 

 present level) for the point of maximum submergence, which gives 

 an average of 4^ fathoms for the period of the deposition of the deep- 

 water clay. This same maximum amount of submergence will bring 

 the top of the Larne gravels 2 feet below high- water mark at the 

 time of maximum depression, which corresponds with the observed 

 nature of the surface-deposits of the Larne section. It may be 

 ai-gued that a smaller amount of submergence would suffice at Larne, 

 inasmuch as the crest of the beach might have accumulated some feet 

 above high water, having been heaped up by storms. To this we 

 may answer that the conformation of the coast at Larne, and of the 

 ground on which this beach was laid down, is against the formation 

 of a storm-beach there ; and further, that against the possibility of a 

 storm-beach may be placed the fact that no allowance has been made 

 for the sagging down which is almost sure to liave taken place on a 

 narrow gravel ridge, exposed since IN'eolithic times to atmospheric 

 agencies and human industries. 



The same difficulty of correlating the deposition-level with the 

 erosion-level, it may be remarked, faces the geologist in Scotland. 

 James Geikie, in dealing with the question of fluctuations of level, 

 concludes that during the formation of the Carses, the sea "attained 

 to a height above its present level of about 50 feet." - Yet the raised 

 beaches belonging to this period of submergence have an elevation of 

 25 feet. Geikie remarks, relative to this point, that in many cases it 



1 See Irish XatHraUst,\o\. xiii., p. 1-16, 1904. 

 - " riebistoric Europe," p. 402. 



