The Irish Post- Glacial Estuari7ie Deposits. 141 



where they are now found, would permit of the accumulation 

 in shallow water of the stratified implement-bearing gravels of 

 lyarne, and the similar deposits at Ballyholme, Greenore, etc. 

 lyow-level raised beaches, such as that at Kilroot, would ap- 

 pear to have been thrown down as the land finally rose. The 

 raised beaches, on account of their greater accessibility and 

 convenience for inspection, have received much more attention 

 from Irish geologists than have the estuarine clays, but I think 

 I have shown that the latter form a far more complete and 

 reliable geological record than can be claimed for the former. 



A few notes of comparison between the fauna of the estua- 

 rine clays and that now existing in the waters of the north- 

 east of Ireland, may possess some interest to the student of 

 conchology. The estuarine clay fauna exhibits a rather more 

 southern aspect than that now living: the difference is not 

 great, and with a few exceptions all the estuarine clay species 

 are known in a recent state in Ireland, but those species which 

 occur in the clays, and are not members of the present fauna, 

 are in general southern forms, so far, at least, as Ireland is 

 concerned. Such species are Tapes decjcssatus, Scrobicularia 

 piperata, Gastrana fragilis, Solent vagijia, Thracia convexa, 

 Nucula sulcata; some of these still live close to the borders of 

 the district, such as in Lough Swilly on the west, and Carling- 

 ford lyough on the south. Solen siliqua, now abundant in the 

 district, has entirely replaced ^. vagina, which is of frequent 

 occurrence in the clays. Rissoa albella, which as a recent 

 British species is confined to Bantr}^ Bay, swarms in the clays 

 at a number of stations in Derry, Antrim, and Down, while 

 R. parva, which is so abundant in our present waters, is found 

 in the cla5\s but sparingly. Odostomia viiiiiina, our smallest 

 and rarest British Odostomia, occurs in numbers, and of com- 

 parativel}" enormous size, in the estuarine clay of Maghera- 

 morne. Jeffreysia opalina, which is onl}^ known as an Irish 

 shell by two dead specimens obtained in Birterbuy Bay, is not 

 rare in the clays at various points. The estuarine claj^ fauna 

 is not only varied, but exuberant, many species attaining 

 therein a size which is not reached by living examples in the 

 district, and which is in some cases quite abnormal. 



It will be seen from what has been said that this series of 

 deposits offers a fertile field of inv.estigation to the geological 

 student, and is well worthy of stud}^ and it is to be hoped that 

 we shall sliortl}^ learn something of similar deposits elsewhere 

 in Ireland. A bed of undoubted estuarine clay occurs at 

 Clontarf, from which Gastrana fragilis, Tapes aui'ens, and 

 Scorbicularia piperata have been recorded ; but there is appa- 

 rently no information obtainable in regard to the presence of 

 these clays at other spots on the coast of Ireland. I trust that 

 this short paper may have the effect of drawing forth some 

 additional facts, and of inducing others to carry on the inves- 

 tigation of the estuarine deposits of Ireland. 



