92 



The Irish Naturalist. 



August, 



southern Europe, but found fossil in the post-Glacial 

 deposits of Denmark and Sweden. 



From a general review of the evidence of the fossil land 

 and marine plants and animals, we can see that in Scandi- 

 navia, in post-Glacial time, there is proof of a warmer 

 period, during which the period of vegetation was much 

 longer than now, and during which the mean temperature 

 was about 2.5^ C. higher. 



As to the precise time of occurrence in the post-Glacial 

 period of the Climatic Optimum there are some differences 

 of opinion among Scandinavian students on the subject, 

 and to determine the time exactly is a matter of considerable 

 difficulty, for while there is a general agreement that it 

 occurred during the period which would include the late 

 Ancylus stage and the early or middle Littorina stage, 

 Gunnar Andersson is inclined to place it definitely in the 

 late Ancylus stage, while Sernander leans to the Littorina 

 stage. Since, however, Gunnar Andersson admits that the 

 exact date of the flooding of the Ancylus Lake by the warm 

 and salt Atlantic waters is extremely difficult to fix, and that 

 the Climatic Optimum of very late Ancylus Age may reason- 

 ably have extended into the Littorina Age, this difference 

 of opinion need not be considered of essential importance, 

 and its main interest for Irish students of post-Glacial 

 fluctuations of climate is that in Scandinavian lands the 

 Chmate Optimum took place in late Ancylus-early Littorina 

 times. As the evidence from the Estuarine Clays of north- 

 east Ireland is almost wholly drawn from a fossil, alluvial 

 marine molluscan fauna, it will be necessary to glance more 

 closely at the western Scandinavian deposits of the Littorina 

 Sea. The name Littorina as applied to the marine depres- 

 sion which succeeded the Ancylus Lake is not wholly satis- 

 factory, for while the expressions " Littorina strata " and 

 " Littorina period " may be usefully applied to the Baltic 

 region, these names are not equally satisfactory for the 

 marine alluvial deposits of Denmark, west Sweden 

 and Norway, characterized by the presence of the 

 southerly warmth loving genera Tapes, Dosinia (Venus) 

 and Ostrea. 



