CLIMATE DURING RECESSION 91 



montana), linden [Tilia europaea), and hazel (Corylus avellana) 

 immigrated almost immediately after the extinction of the 

 arctic flora and occurred in the whole of southern Sweden in 

 early post-glacial time, that is to say about 2,000 years after the 

 release of the ice (von Post, 1916). At the present time alder 

 and elm occur to beyond the 65th parallel of latitude, and linden 

 and hazel in the coast region up to the 63rd parallel, or central 

 Norrland. In northern Sweden the land was from the beginning 

 occupied by a temperate pine flora, essentially similar to the pre- 

 sent vegetation of the region (von Post, 191 1, p. 20). Thus the 

 amelioration of the climate, in late glacial time, became more 

 and more noticeable. Towards the end of the epoch the arctic 

 belt, which had previously followed the retiring ice edge, had 

 ceased to exist. 



The Varve Studies As a Key to Climatic Periodicity 



The clay studies, when they shall have been carried out in 

 detail, will increase our knowledge of climatic periodicity. They 

 furnish perhaps the best material known for the study of long 

 periods and one of the best for that of short ones. Since the 

 disappearance of the ice was due to climatic reasons, the perio- 

 dicity in climate is recorded by the annual amount of ice melting, 

 the rate of recession of the ice edge — recession, halt, and re- 

 advance — and the amount of sedimentation (cf. pp. 85-88). 

 The short periods, that is to say those up to a few decades in 

 length, are best illustrated by the amount of sedimentation, by 

 the varve graphs. The long cycles are shown by the rate of 

 recession. 



Study of the climatic periods is one of my chief purposes in 

 measuring so great a number of sections and working out the 

 normal curve. For the elimination of local, non-climatic features, 

 material from different lakes is necessary. Therefore at present 

 only parts of the normal curve are fit for the analysis of periods ; 

 other parts may be perfectly good but should be controlled. 

 For the analysis of long periods, more detailed studies of the 

 rate of ice retreat are necessary. While time has not permitted 



