THE PEAT CLISTASE. 



397 



was of the briefest extent. After the fourth glacial period followed a long 

 interglacial period with hot and dry summers, during which the loess was 

 formed. This was succeeded by a climate very like the present, and this by 

 the fifth glacial period. 



According to Gradmann (1910), it is at least necessary to recognize a post- 

 glacial xerotherm period, in spite of the fact that Penck regards the loess as 

 interglacial. He emphasizes especially the connection of prehistoric people 

 with plant communities of predominantly southeastern distribution. In 

 general, at this time, a continental climate prevailed, which was favorable to 

 steppe rather than to forest. The essential point lies in the fact that forest 

 was inimical to the steppe communities as well as to the human ones. The 

 main proof for the xerotherm climate hes in the limiting horizon of the north 

 German moors, in the occurrence of remains of the wild horse beneath Neo- 

 lithic culture remains, etc. 



Krause (1910) holds that the beech has invaded the lands along the East Sea 

 as a consequence of other .causes than chmatic ones such as a cooHng after the 

 oak period. The pine was largely replaced by the oak at the end of the 

 Ancylus period, and its present extension is solely a consequence of forestation. 

 The postglacial dry period assumed by Andersson accords with the conditions 

 in Germany as well as with Briquet's xerotherm period, but Krause assimies 

 that it had nevertheless a subglacial cUmate. He considers that all the phy to- 

 geographical problems can be explained on the assumption that the first part 

 of the postglacial period had a cool dry climate, and the latter part the climate 

 of the present. 



With reference to the climatic problem, Ramann (1910) reaches the conclu- 

 sion that the change of the high moor can be explained by a rise of the ice- 

 layers imder the vegetation. In the peat-moors of middle Europe the change 

 of vegetation and hence of layers is determined by the physical properties 

 of the peat, and the assumption of a change of climate is unnecessary. 



Weber (1910) considers that the sequence of Alnetum, Pinetum, and Sphag- 

 netum peats in the moors of North Germany does not indicate a change of 

 climate, but that the so-called horizon-peat between the lower and upper 

 Sphagnum peat does indicate such a climatic change. The horizon-peat must 

 have been built after the Litorina subsidence and about the end of the later 

 Stone Age. 



StoUer (1910) considers chiefly the appearance of single plants and plant 

 communities after the glacial period. He regards the Yoldia period and the 

 Ancylus period as together forming the older alluvium, while the Litorina 

 period and the present correspond to the later alluvium. After the relatively 

 short period of cold, dry chmate, during which the ice melted, came the birch- 

 pine period, followed by the oak period, which falls in the time of the formation 

 of the horizon-peat and the beginning of the Litorina period. The alder-beech 

 period with warm moist climate prevailed in Germany to the middle of the 

 Litorina period. 



Graebner (1910) opposes the relict concept. If the northern forms living on 

 the high moors are to be regarded as reUcts of the glacial period, then a marked 

 climatic change could hardly have happened after the disappearance of the ice 

 He cautions also against assuming the presence of climatic changes from the 

 regular sequence in the moors. 



