PLANT REMAINS IN PEAT MOSSES 323 



trees and an assemblage of plants quite typical of any marshy 

 lowland forest region in Britain at the present time. 



If it be contended that the Lower Forestian is due to local 

 changes in climate — such as variation in snowfall, direction of 

 wind — how is it that the bed maintains its character not only 

 in the south of Scotland, but also in the Outer Hebrides and 

 Shetland Islands ? 



If the succession of the first arctic by the Lower Forestian, 

 lower peat bog, and second arctic bed were really due to local 

 causes, widely separated districts should show different suc- 

 cessions ; while, for instance, tundra vegetation would be 

 represented in one district, the remains of a forest vegetation 

 would occupy the same horizon in another. But this is not 

 the case, for nothing is more striking than the continuity of the 

 horizons. The chief points for consideration may be stated as 

 follows : 



(a) First Arctic Bed. — Lower limit of arctic-alpine vegeta- 

 tion depressed to sea-level. 



(b) Lower Forestian. — Upper limit of deciduous trees raised 

 to at least its present level. 



(c) Second Arctic Bed. — Lower limit of arctic-alpine vege- 

 tation depressed to sea-level. 



(d) Upper Forestian. — Upper limit of trees raised to over 

 3,000 ft. 



These changes are post-glacial in the sense that they occurred 

 later than the last ice-sheet. It is difficult to reconcile these 

 changes with the " gradually waning glaciation, during which 

 there were occasional local advances of the mountain-glaciers 

 in their glens due to temporary increase of snowfall " suggested 

 by Lamplugh (12). The beds rather indicate a definite sequence 

 of events which took place simultaneously over the whole of 

 Britain. Local changes of snowfall and local retreat and advance 

 of glaciers almost certainly occurred during the later stages of 

 the glacial period ; but these could hardly bring about the wide- 

 spread alternate depression and elevation of the limits of an 

 arctic-alpine flora shown by the peat. It matters little whether 

 these stages are spoken of as local changes during the waning 

 glaciation or are expressed as glacial and inter-glacial stages ; 

 the fact remains that the climatic fluctuations were lengthy and 

 pronounced enough to change the distribution of the flora in the 

 north of Britain. 



