88 



The Irish Naturalist. 



August, 



and thxC post-Glacial peat bogs, lake deposits, marginal 

 marine muds, and the raised beaches. The intensive 

 study of these very late formations has been carried on in 

 Scandinavia in recent years with the result that as regards 

 these beds we are now in a position to formulate a fairly 

 reasonable scheme showing the succession of events since 

 the decay of the great European glaciers of the Ice Age. 



A definition of the change of climate included in the 

 phrase " post-Glacial climatic optimum " is desirable and 

 we cannot do better than to accept the one brought forward 

 by Gunnar Andersson, the leading Swedish authority on 

 the subject. His definition is as follows : — "At the end of 

 the late-Glacial period, the warmth increased for a long 

 stretch, so that the temperature of Scandinavia became 

 not only as favourable as now, but even considerably 

 warmer ; follovv^ing on that maximum, the temperature 

 sank again. It will be seen from this definition that we 

 are dealing v\'ith one of the later phases of the post-Glacial 

 period and our attention will be mainly directed to the middle 

 and later stages of the Ancjdus period, and the early and 

 middle stages of the Littorina period. 



The post-Glacial geological history of Scandinavia may 

 be divided into three main periods and to these periods 

 approximate geographical outlines and climates have been 

 ascribed, and ¥/hile much remains to be investigated in the 

 geographical and climatic conditions of these periods, the 

 following general statement may be taken as a sufficient 

 account of the subject for our present purpose.^ 



The decay of the latest ice-sheet found the Scandinavian 

 peninsula isolated from the rest of Europe by a sea which 

 stretched across the lower levels of Norway, Sweden, and 

 Russia from the Atlantic Ocean to the White Sea. In 

 the stratified marine deposits of this sea-shells of an arctic 

 type have been found in abundance, and from its most 

 characteristic mollusc, Portlandia ( Yoldia) arctica, it has 



1 Gunnar Andersson : Swedish climate in the late-quaternary period, 

 see pp. 247-300, Die Veranderungen des Klimas, 1910. 



-W- R Wright; The Quaternary Ice Age. London, 1914. 



