PLANT REMAINS IN PEAT MOSSES 319 



of Scotland the forest consists of Pinus sylvestris, with the 

 exception of some parts of Tweedsmuir, where Behila alba 

 replaces pine. As soon as the Highland areas are entered the 

 Upper Forest divides into two distinct zones separated by 1 — 3 ft. 

 of peat in which no wood is found. In the Spey-Findhorn, 

 Findhorn-Nairn, and Coire Bog districts the peat between the 

 upper and lower layers of this forest is formed from Sphagnum, 

 but in areas examined in the Grampians, and in Assynt, Betula 

 nana and Salix arbuscula are abundant between the two layers 

 of forest remains. The presence of these plants in some 

 districts and of Sphagnum beds in others, between two layers 

 of well-developed pine forest, is significant, and points to a 

 decided break in forest conditions at this time. This phenomenon 

 is too widespread to be due to local causes, for it is a constant 

 feature in all the Highland areas examined. 



Betula alba replaces Pinus sylvestris in the lower zone of the 

 Upper Forest on the Grampians, in Assynt, and over much 

 of the Caithness-Sutherland border — in other words, at high 

 elevations and in the extreme north. It is remarkable that until 

 the Upper Forest is reached no extensive beds of Calluna are 

 found. The Vaccinium-Calluna association, now so constant a 

 feature on moorlands in Scotland and England, appears to be 

 a comparatively recent feature. 



The Peat above the Upper Forest. — The peat of varying thick- 

 ness lying above the Upper Forest presents the same features 

 as the lower and upper peat bog. Occasional beds of Calluna 

 or Eriopliorum make their appearance, but are not continuous 

 over large areas, and are evidently due to local causes. The 

 general flora is of a distinctly wetter type than that characteristic 

 of many of the peat areas of the present time, as it consists 

 mainly of Scirpus cocspitosus and Sphagnum. 



During the last thirty years much work has been done 

 in Britain by various investigators upon plant remains in 

 Pleistocene beds, and such work is admirably summarised in The 

 Origin of the British Flora, by Mr. Clement Reid. A detailed 

 account would be out of place here, but reference may be made 

 to some of the districts yielding arctic plants. 



It is obvious that the number of arctic horizons in Pleistocene 

 and post-Pleistocene deposits cannot be indefinite, and therefore 

 some of the arctic beds in peat and alluvial deposits may be 

 contemporaneous with either one of the arctic zones in the 



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