PLANT REMAINS IN PEAT MOSSES 315 



arctic species again appear as the strata above the Lower 

 Forest are reached ? 



The upward limit of tree growth has been used both in 

 Britain and on the Continent as the approximate boundary 

 between the sub-alpine and alpine floras, and it is found that 

 a considerable difference in altitude separates the zone of 

 natural woodland from the alpine associations. 



From this, the first arctic bed appears to be the result of 

 the depression of the present alpine-arctic boundary in Britain 

 to the extent of about 2,000 ft., whilst the Lower Forest zone 

 represents the return of that boundary to at least its present 

 altitude. 



The absence of these two beds from the Highland districts 

 is remarkable. Either conditions were not favourable for peat 

 formation in those areas during the first arctic, the Lower 

 Forestian, and the lower peat bog period, or peat formed 

 during those periods was subsequently removed either by 

 glaciation or by atmospheric agencies. Further areas must 

 be examined before it is possible to say which view is correct. 



At the same time it must not be forgotten that water action 

 frequently plays a great part in the removal of peat beds. 

 Many cases have come under notice in various parts of Scotland 

 and the north of England where the older beds along a stream- 

 side have been swept away and replaced by mounds of sand 

 and gravel. One example is found at a sharp bend in the 

 Abhuinn-a-Coire-Bhuig in Eastern Ross, where all the older 

 peat beds have been washed away and replaced with sand 

 and gravel. This event occurred before the Upper Forestian 

 and most probably during the upper peat bog stage. It is 

 not of course suggested that the absence of the older peat 

 beds throughout the Highlands can be due to water action 

 of this character, but the example is given in order to emphasise 

 the many occurrences which may be responsible for the absence 

 of the older beds of peat in some districts. It is quite evident 

 that peat formation is dependent upon many factors such as 

 temperature, humidity of climate, drainage, character of soil, 

 and the flora, or the peat deposits of Britain would not be 

 so local in distribution. 



No trace of Pinus sylvestris has been found in the Lower 

 Forest, although it is the most characteristic tree of the Upper 

 Forest. If native in Scotland at that time, it is difficult to see 



