350 MR FRANCIS J. LEWIS 



The upper forest zone in this district consists of an upper and lower layer of Pinus 

 sylvestris, separated by about \\ feet of Sphagnum peat. This doubling of the pine 

 zone has now been noticed in several distinct areas in the North of Scotland ; it is a 

 constant feature over Coire Bog in Easter Ross, on the Findhorn-Nairn watershed and 

 over large areas in the fifty miles of country lying between Tongue on the north and 

 Lairg in the south. Both the upper and lower layer of pine are similar in character — 

 both contain abundant remains of Calluna, whilst the intervening peat is formed of 

 Sphagnum, with scarcely any trace of Calluna or other plants. If this feature was only 

 developed over small areas and in patches it might well be due to local alterations in 

 drainage and the formation of small boggy pools in the pine forest, but its widespread 

 character does not lend any support to this view. Two possible explanations occur : 

 (a) either the lower layer of pine exhausted the food supply in the peat, decayed, and 

 was buried by a layer of Sphagnum, the regenerated moss being again covered with 

 pine in the manner described by Gunnar Andersson in reference to the Swedish moors ; 

 or (b) the alternation of pine, Sphagnum and pine may indicate some climatic change. 

 Were the former view correct we might have expected to find that some of the large 

 areas in Southern Scotland where the pine zone is well represented would show the 

 same feature. So far, however, the duplication of the upper forest zone is confined to 

 districts in the North of Scotland. For this reason the author suggests that the 

 phenomena may be due to some climatic change. Following the formation of the upper 

 forest zone, there seems to have been a recurrence of cold conditions, just sufficient to 

 produce small glaciers in corries lying above 3000 feet. Whilst this small glaciation of 

 the highest ground in Britain would not change the distribution of the flora over the 

 lower-lying parts of the country, it must have resulted in a greater precipitation, and 

 tended to restrict the forest areas — particularly over the peat mosses. This change 

 would be more marked in the North and West, and must have decreased rapidly towards 

 the South and the lowland tracts. In this view the lower layer of the upper forest zone 

 would represent the upper forest zone of the Southern Uplands, — the overlying 

 Sphagnum beds would indicate the general character of the peat-moss flora during the 

 corrie-glacier period ; while the upper layer of pine above the Sphagnum beds would 

 represent drier conditions occurring some time after the passing away of the cold phase. 

 The cause of the second invasion of the peat mosses in the Highlands by pine forest, and 

 their non-invasion in the Southern Uplands after the corrie-glacier period, might point 

 to Pinus sylvestris having at this period died out in the South. At the present day, as 

 is well known, no forests of Pinus sylvestris are native in Southern Britain, primitive 

 pine forest being almost restricted to the area north of the Forth. This condition of 

 things may date from the upper forest-bed. That the period following immediately 

 after the corrie-glacier period was not characterised by great precipitation is supported 

 by the fact that the mosses resting on the 2 5 -feet raised beach contain much Corylus 

 Avellana and Betula alba. Reading the upper layer of pine as post-corrie-glacial, that 

 bed would be contemporaneous with the Corylus and Betula layer of the 25-feet raised 



