ON THE PLANT REMAINS IN THE SCOTTISH PEAT MOSSES. 67 



(c) Second Arctic Bed. Lower limit of arctic-alpine vegetation depressed nearly 

 to sea-level. 



(d) Upper Forestian. Upper limit of trees raised to over 3000 feet above 

 sea-level. 



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 Lampltjgh (12). 



The beds rather indicate a definite sequence of events which took place simultane- 

 ously 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 widespread 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. 



As the arctic beds contain plants indicative of cold and wet conditions, the 

 probability is that glaciation took place in elevated regions during their deposition. 

 The Lower Forestian contains a flora indicating conditions at least as temperate as the 

 present day, and the Upper Forestian shows an elevation of the upper limit of forest 

 far above that of the present day. 



In Sweden a similar elevation of the upper limit of forest to the extent of 1100 

 feet (300 m.) took place during post-glacial times, and Gunnar Andersson concludes 

 that the arctic-alpine flora then disappeared from the lower mountain ranges. My 

 own observations in Scotland would place the difference between the upper limit of 

 trees during the Upper Forestian and at the present day at not much less than 2000 

 feet in the Highlands ; in Cumberland and Westmorland at rather more. It is 

 possible that glaciers still lingered on in many parts of the Highlands during the earlier 

 stage of the forest periods ; this would be more likely in the case of the Lower Forestian 

 than the Upper Forestian. 



The question of climate during the Pleistocene epoch has been discussed by Harmer 

 (16) in an interesting and suggestive paper, and the conclusion is reached that a change 

 in the direction of prevalent winds, due to different relative positions of areas of high 

 and low barometric pressure, may account for the comparatively low temperature and 

 high precipitation during some stages of the Pleistocene period. The observations from 

 Shetland certainly show a difference in the direction of the prevalent winds during the 

 [Lower Forestian. 



While it is difficult to reconcile the several stages in the peat with the theory of 

 a single glaciation, the whole of the peat beds agree very closely with the scheme of 

 classification proposed by Geikie (17). In that scheme the First Arctic Bed and Lower 



