October, 1902. 229 



A CONTRIBUTION TO THE GLACIAL GEOLOGY OF 



COUNTY DUBLIN. 



BY J. DK WITT HINCH. 



[Read before the Dublin Naturalists' Field Club, March 5, 1901.] 



In 1874 Rev. Maxwell H. Close contributed to tlie Geological 

 Magazi7ie^ an account of the high-level glacial drift of County 

 Dublin. In that paper the author describes these upland 

 deposits of shelly drift, which occur on the Dublin hills at 

 levels varying from 850 to 1,200 feet. In this paper is given 

 a list of marine mollusca, found in the sand and gravel beds 

 near Ballyedmonduff at an elevation of over 1,000 feet above 

 sea level. 



Since 1874 investigations into the nature of the lowland 

 glacial deposits have taken place from time to time, two of 

 which call for special mention : — The reports of the British 

 Association Committee on the *' Manure" Gravels of Wexford, 

 the second" of which gives a list of marine mollusca obtained 

 from the shelly gravels near Ballybrack on the edge of the 

 sea ; and papers on Irish glacial deposits b}'- Prof W. J. Sollas 

 and Mr. Lloyd Praeger, the second^ of which deals with the 

 Kill-o'-the-Grange beds and give lists of marine mollusca and 

 foraminifera collected from these sections, which lie at an 

 elevation of 150 feet above sea level. 



A very curious point about these shell-bearing deposits was 

 the fact that between the Kill-o'-the-Grange and less elevated 

 beds, and those of Glendoo Wood at a level of 700 feet higher, 

 a complete gap appeared to exist. Messrs. Sollas and Praeger 

 found chalky shell remains near Rathfarnham, but above this 

 there was nothing to connect the low level and high level 

 shelly drifts. 



The present paper is an account of work undertaken to 

 obtain more evidence as to a possible connection between 

 these two sets of beds — to see if satisfactory evidence could 

 be brought forward to lessen the gap between them. With 



"• The elevated shell-bearing gravels near Dublin : Geological Magazine, 

 1874, p. 193. 



2 British Association Report, 1888, pp. 139-140. 



3 Irish Naturalist^ Dec, 1895. 



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