88 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



migrate from the northeast until much later — after the ice- 

 cap had melted in the north of Norway and Sweden, and then 

 made its way southward. The common Pinus sylvestris, on 

 the contrary, as we have said, undoubtedly migrated into 

 Norway from the southeast through Sweden, which is prob- 

 ably the way by which most of those species immigrated which 

 are now found growing with it in the southeast of Norway. 



THE QUERCUS PEDUNCULATA PERIOD 



The climate gradually becomes warmer, the inland ice has 

 quite disappeared, and simultaneously with its disappearance 

 the land in a belt across central Sweden begins once more to 

 sink (the Littorina Subsidence). When this subsidence cul- 

 minated, the south of Sweden was a great island which, on 

 the south, was separated — as it now is — from Denmark by 

 Oeresund and by a broad arm of the sea, which ran from 

 Skagerak through the district in which the lakes Venern and 

 Vettern now lie right to the Baltic. This sea thus acquired 

 an opening into the North Sea, and its waters gradually be- 

 came salt. 



This subsidence of the land, which took place when the 

 land around Kristiania was about 230 feet lower than it now 

 is, did not greatly affect Norway, for it amounted in the latter 

 to only a few yards. But it may probably be assumed that 

 so great an arm of the sea, with a current of Gulf Stream 

 water that even brought Gulf Stream nuts (Entada giga- 

 lobium) with it to the shores of Bohuslaen — whence they are 

 not carried at the present day — must have made the climate 

 warmer and more insular than it now is. Before the sub- 

 sidence, then, the climate must have been warm and dry, after 

 the subsidence, warm and damp. 



How much warmer the climate must have been is apparent 

 from Gunnar Andersson's investigations— following the dis- 

 covery of fossils — on the distribution of Corylus Avellana at 

 that time, compared with its present distribution. It appears 

 that the mean temperature of the summer months must have 

 been about 2.5°C. higher than it now is. In the sea off the 

 coast of Norway there lived at that time species of the more 



