PLANT REMAINS IN PEAT MOSSES 313 



represented by this bed, was much later than the main ice- 

 sheet. 



In a recent account of the development of the Scandinavian 

 flora, Gunnar Andersson (4) records the occurrence of Potamo- 

 geton filiformis, P. prcelongus, Menyanthcs trifoliata, Batrachium 

 confervoides, and other aquatic plants in the Dryas Zone, and 

 infers that the Scandinavian climate of that time was not arctic 

 like that, for instance, of North Greenland, but rather resembled 

 South Greenland at the present time. This conclusion is in 

 complete agreement w T ith the features found in the north- 

 west Highlands. Each arctic stage appears to mark a period 

 of great precipitation, and these apparently alternated with 

 comparatively dry temperate stages. The character of the 

 first arctic bed is different in the Outer Hebrides — the only 

 other district in which the peat is old enough to go back to 

 this date. In Lewis, the older layers contain Salix arbuscula, 

 Betula nana, Potentilla Comarum, Empetrum nigrum, Menyanthcs 

 trifoliata, Potamogeton sp. 



Some of these are plants of wide distribution from temperate 

 to arctic regions : others like Betula nana and Salix arbuscula 

 have an entirely arctic or sub-arctic distribution, and do not 

 now occur near sea-level in Britain ; but these basal beds 

 suggest less rigorous conditions than those in the Shetlands, 

 for bog plants of wide distribution are the most abundant, whilst 

 in the Shetlands Salix reticulata is the characteristic plant. 



The plants of the first arctic bed must have immigrated 

 to Scotland either across the North Sea or through England. 

 The incoming flora would probably pass along the higher 

 ground while the valleys and lowlands were still covered 

 with the shrinking remnants of the local ice-sheets. The 

 evidence from the mosses in Lewis certainly suggests that 

 the incoming arctic flora barely established itself in the 

 extreme west of Scotland before the Lower Forest overspread 

 the peat bogs, as the typical arctic plants represented in 

 Shetland are either absent or poorly represented in the 

 corresponding zone of the Hebrides. 



The Lower Forcstian. — Considerable interest attaches to the 

 flora of this zone, owing to the absence of any arctic or 

 sub-arctic plants, suggesting that a complete change of con- 

 ditions took place between the first and second beds, during 

 which the arctic flora withdrew from the peat areas. 



