[Vol. 2 



80 ANNALS OK THE MISSOURI BOTANICAL GARDEN 



in central Sweden, and in the south of Norway to the morainic 

 ridges that extend from Fredrikshald to Moss, Horten, 

 Arendal, etc., and are designated by the Norwegian word 



<<T?„ >» 



Ra. 



According to G. de Geer, these great terminal moraines 

 must have been formed about 9,000 years ago when the inland 

 ice stood still along that line for a period of about 350 years. 

 It is a matter of indifference to us that other geologists be- 

 lieve that this "Ra" period occurred somewhat earlier. 



What is of great importance in the immigration of the ilora, 

 however, is that the extreme southeast of Norway and the 

 center of Sweden, at the time of the "Ra" formation, lay 

 much lower than at the present time, and sank still lower 

 some time after the ice withdrew. It is supposed that the 

 sea near Kristiania, during the "Ra" period, was about 660 

 feet higher than it now is, and a little later rose to 720 feet 

 above its present height, which is the highest limit of the late 

 glacial sea. But this limit differs in different parts of the 

 country; it falls toward the coast, especially toward the 

 west coast of Norway. At Larvik, for instance, it is about 

 426 feet; at Arendal, 246 feet; at Kristianssand, about 130 

 feet; at Mandal, 82 feet; and at Farsund, only 28 feet. 

 Farther north it increases again, so that at Kristianssuad it 

 is about 246 feet, and at Trondhjem, 650 feet, or almost as 

 great as at Kristiania. 



THE DRYAS PERIOD 



I 



have previously ('05) endeavored to show by Dry as and 

 Salix polaris, which A. G. Nathorst has found in a fossil state 

 in the south of Sweden, that the arctic flora cannot have made 

 its way thence into Norway; for during the "Ra" formation 

 the masses of ice went right out into the sea, and when the 

 ice had withdrawn far enough to leave open land w T ithin the 

 "Ra" line, the climate had already altered to such an extent 

 that the arctic flora was extinct in the south of Sweden. 



The earliest plants of which J. Holmboe ('03) has found 

 remains in the southeast of Norwav, prove also to be sub- 



