96 



The Irish Naturalist. 



August 



the general withdrawal to the south of the species named, 

 but we are now dealing certainly with the partial collapse 

 of a fauna, and the disappearance from a old habitat of 

 many of its most abundant elements, as the result of a 

 change of climate. It has to be borne in mind that the 

 above list of species does not include any of the most striking 

 instances of withdrawal to the south, such as Gastrochaena 

 dubia, with its present distribution in Ireland limited between 

 Tramore in Waterford and Roundstone in Connemara; it 

 is a list of animals, which having flourished in immense 

 numbers and exuberance of form in the late post-Glacial 

 seas of north-east Ireland are now represented there only by 

 a depauperated and sparsely distributed remnant. Among 

 the species still inhabiting north-eastern waters, but dis- 

 tinguished for their great size and immense numbers- in the 

 Estuarine Clays the examples of the Oyster and of Turritella 

 terehra may be recalled. What change j^f distribution took 

 place as regards the fauna of the Raised Beaches is a much 

 more difficult one as we have not the quantitative evidence 

 available from the Estuarine Clays to build upon, but here 

 also a number of instances are known which support the view 

 of a considerable withdrawal of marine animal life to the 

 southward since late post-Glacial time. It is not proposed, 

 at present, to institute a comparison between the late post- 

 Glacial deposits of Scandinavia and those of Ireland, but 

 the general agreement is obvious, and while we cannot say 

 whether the Estuarine Clay beds were laid down at the time 

 of the Climatic Optimum, or at some later period, we are at 

 least justified in saying that the abundant occurrence of 

 the southern mollusca in these beds may be accepted as 

 proof of a considerable improvement of climate since the 

 Glacial Period, an improvement which has not been main- 

 tained, judging by the present-day more southern distribution 

 of many marine animal forms. 



Geological Survey Office, Dublin. 



