QUATEEXARY DEPOSITS OF BRITISH ISLES BROOKS. 



349 



divides the occurrences into a number of zones, which, with their 

 climatic vahies and their probable equivalents in the sequence of 

 floras and in the Baltic periods, he tabulates as follows: 



Reference must be made also to a paper by R. Stahl (116) in 1913, 

 in which fluctuations of water level in lakes and rivers, attributed by 

 him to the rising and falling of the Baltic, were demonstrated on 

 archeological grounds. Neolithic dwellings of the beginning of the 

 Litorina period in Lake Drewitzer were submerged later to a depth 

 of 5 to 6 meters. In the "Wendian" period the water again sank so 

 low that the island of Wend was habitable. He places the Grenztorf 

 at the beginning of the Litorina period. 



In the face of this diversity of opinion it is difficult to frame a 

 working idea of the course of events, but a few points may be men- 

 tioned. In the first place, it seems fairly certain that since glacial 

 times there have been two dry periods in north Germany. The first 

 of these occurred soon after the' retreat of the ice from the German 

 coast, and probably while it still occupied part of the Baltic. East 

 and northeast winds acting on the materials left behind, built up 

 dunes concave toward the west, which have subsequently had their 

 slope but not their shape modified by west winds, as described by 

 Solger and Svastos (IIT) . The climate was still subarctic, but as ele- 

 vation had already commenced in north Germany this stage is often 

 attributed to the Ancylus period, though it corresponds in phase only 

 and not in time to the Ancylus period of Scandinavia. When the 

 elevation extended into Scandinavia and the Baltic became the fresh- 

 water Ancylus lake, the ice was retreating rapidly under a climate 

 which was by no means subarctic, but which was distinctly dry and 

 continental. 



Thus the beginning of the Ancylus period in Scandinavia was 

 marked by a dry climate probably due both to elevation and to the 



