THE PEAT CLISTASE. 



393 



mountain-glaciers in their glens due to temporary increase of snowfall' 

 suggested by Lamplugh. 



"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 Umits of an arctic-alpine flora 

 shown by the peat. 



"It matters Uttle whether these stages are spoken of as local changes durmg 

 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 

 probabihty is that glaciation took place in elevated regions during their depo- 

 sition. 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 

 1,100 feet (300 m.) took place during post-glacial times, and Gimnar Andersson 

 concludes that the arctic-alpine flora then disappeared from the lower moun- 

 tain ranges. My own observations in Scotland would place the difference 

 between the upper limit of trees diuring the Upper Forestian and at the present 

 day at not much less than 2,000 feet in the Highlands; in Cmnberland and 

 Westmoreland at rather more. It is possible that glaciers still lingered on in 

 many parts of the Highlands during the earUer 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 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. In that scheme the 

 First Arctic Bed and Lower Peat Bog would mark the gradual passage of the 

 Mecklenbm-gian stage into the Lower Forestian, the Second Arctic Bed would 

 represent the Lower Turbarian, and the Upper Forest in the peat would corre- 

 spond with the Upper Forestian or Fifth inter-glacial stage. 



"All the Scottish peat mosses show a definite succession of plant remains. 

 The oldest, in the south of Scotland and the Shetland Islands, have an arctic 

 plant bed at the base. This is succeeded by a forest of birch, hazel, and alder 

 containing temperate plants. A second arctic plant bed occurs above the 

 Lower Forest and is overlaid in all districts (except the Hebrides, Cape Wrath, 

 and the Shetland Islands) by an Upper Forest covered by several feet of 

 peat-bog plants." 



Weber (1907) has described in concise fashion the life-history of a represen- 

 tative moor, as shown by the successive layers of peat: 



The most complete series are found in moors which have arisen in waters 

 rich in solutes, and especially in those in which the formation of peat began 



