3 2 4 SCIENCE PROGRESS 



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 i,iooft. (300m.) took place during post-glacial 

 times, and Gunnar Andersson concludes that the arctic-alpine 

 flora then disappeared from the lower mountain ranges. Obser- 

 vations in Scotland would place the difference between the 

 upper limit of trees during the Upper Forestian and at the 

 present day as not much less than 2,000ft. 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 stages of the forest periods; 

 this would be more likely in the case of the Lower Forestian 

 than in the Upper Forestian. 



The question of climate during the Pleistocene epoch has 

 been discussed by Harmer (13) 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 period. 



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 (14). In that scheme the first arctic bed and lower 

 peat bog would mark the gradual passage of the Mecklenburgian 

 stage into the Lower Forestian ; the second arctic bed would 

 represent the Lower Turbarian ; and the Upper Forest in the 

 peat would correspond with the Upper Forestian or fifth 

 inter-glacial stage. 



References 



1. Nathorst, A. G., Uber den gegenwartigen Standpunkt unserer kenntnis von 

 dem Vorkommen fossiler Glacialpflanzen, Bihang till K. Svenska Vetenskaps 

 Akadcmiens Handlingar, Stockholm, 1 891, iii. 



