3 o8 SCIENCE PROGRESS 



Sweden, an extensive literature dealing with this subject has 

 grown up in Norway, Sweden, Denmark, Germany, and Switzer- 

 land. In Scandinavia particularly, the work of Nathorst, Gunnar 

 Andersson, Wille, A. Blytt has made it possible to trace the 

 path followed by the flora, as it immigrated during the shrinkage 

 of the ice-sheet, to gain some idea of its gradual change in 

 distribution during succeeding epochs and to reconstruct the 

 climatic changes which occurred during post-glacial times. 



The general sequence of the plant remains in the Swedish 

 peat may be briefly described. At the base, the remains of an 

 arctic flora have been found enclosed in fresh-water clays and silt. 

 The flora consists of Dry as octopetala, Salix polaris, S. hcrbacea, 

 S. reticulata, S. arbuscula, Behda nana, Arctostaphylos alpina, 

 Empetrum nigrum, Diapensia lapponica, Myrtillus uliginosa, and 

 other plants of a like arctic character. Owing to the abundance 

 of Dryas remains, this zone is generally spoken of as the Dryas 

 Zone. This flora had a wide distribution during late glacial 

 times, as it has been discovered in Sweden, Norway, Denmark, 

 Germany, and Russia. This basal arctic vegetation is overlaid 

 by a considerable thickness of peat containing the remains of 

 four forest-beds. The lowest, immediately overlying the Dryas 

 Zone, was formed chiefly of birch {Betula odorata, B. subalpina, 

 B. tortuosa), with aspen poplar {Populus tremula), juniper, and 

 a few species of willow. The accompanying flora is subarctic 

 rather than arctic. The birch zone is succeeded by three 

 separate forest beds of pine (Pinus sylvestris), oak {Quercus 

 robur), and spruce {Picea excelsa) respectively. 



In the British Isles the present distribution of peat deposits 

 shows a general tendency to follow the maximum rainfall, the 

 deposits being comparatively scanty on the eastern side of 

 England and Scotland, and increasing in area and thickness 

 as the western coasts are approached — the greater development 

 occurring in the Hebrides, the western part of the Scottish 

 mainland, and in the west of Ireland. In the hill districts they 

 reach their greatest development upon smooth, flat-topped hills, 

 like the Pennine chain in England, the elevated plateaux of the 

 Grampian mountains, and in elevated districts surrounded by 

 mountains, such as the moor of Rannoch in the west of 

 Scotland. 



Yet if the peat in such districts is examined, it is found that 

 there are traces everywhere showing that the present conditions 



