1 92 1. HiNCH — Post-Glacial Climatic Optimum in Ireland. 91 



Gunnar Andersson has dealt h with in a detailed monograph. 

 This tree has been found in a fossil condition in 275 localities 

 north of its carefully determined actual northern boundary at 

 the present time, and it is estimated that it has been forced 

 out of a territory of over 84,000 square kilometres since the 

 time of its widest distribution during the Climatic Optimum. 

 A very careful examination of occurrence of the Hazel in 

 relation to the present climate, has led to the conclusions 

 that the period of vegetation during the time of its widest 

 distribution was 2.4^ C. warmer than the present day, and 

 that in the Climatic Optimum the autumn was warmer and 

 longer than is the case now. With the Hazel may be placed 

 a number of trees and shrubs which have been likewise 

 pressed back from the northern limit they once reached, 

 and among these may be mentioned the Oak (the charac- 

 teristic forest tree of the Littorina period), the Linden, the 

 Elm and the Beam-tree, while a very large number of 

 southern species of trees and shrubs now only occur in 

 specially warm and favourable localities ; in fact we 

 must regard them generally as relics of a bygone warmer 

 period. 



Among the plants of this warmer time may be mentioned 

 the Water-nut {Trapa nutans) a plant which belongs to the 

 flora of the south of Europe and already rather rare in north 

 Germany. The easily recognised nuts of this plant have 

 been found fossil in Sweden in the peat-bogs as far north as 

 the valley of the Malaren, and it has been found fossil also 

 in many places in Denmark, West Prussia, Sweden and 

 Finland. In the Swedish flora the Water-nut has only one 

 relic station, in Lake Immeln in north-east Skane. As 

 in the case of the trees and shrubs there are a large number 

 of plants which only occur in warm and sheltered localities 

 and must be considered as relics of a once wider distribution 

 of the species. 



In addition to the forest trees, shrubs and herbs, a number 

 of animals — mammals, insects, fresh-water and land mollusca, 

 also immigrated into Scandinavia during the Climatic 

 Optimum, the most striking instance being the land tortoise 

 Emys lutaria, at the present day confined to central and 



