ON THE PLANT REMAINS IN THE SCOTTISH PEAT MOSSES. 347 



Section III. : — 



Dominant Plant. 



1. Eecent peat. 



2. Pinus sylvestris, L. 



3. Sphagnum peat. 



4. Betula alba, L. 



5. Glacial deposits. 



It will be seen that Sections I. and II. show almost exactly the same sequence of 

 plant remains. The basal beds differ, however, in the two cases. 



The history of events in Section I. appears to have been as follows : — After the 

 passing away of the glaciers which occupied the Highland valleys, the first vegetation 

 clothing the barren summits and flanks of these hills was essentially Arctic in character, 

 consisting in some places of a close growth of S. reticulata with S. herbacea, together 

 with such Arctic- Alpine plants as Lychnis alpina, Veronica alpina. This early growth 

 of an Arctic flora did not cover the whole ground, for it is absent from many of the 

 sections taken on the same watershed. It appears to have formed patches of vegetation 

 on the otherwise bare ground, in much the same way as is found at the present day on 

 high northern tundras. In describing the high northern tundras of Taimyr, Middendorff 

 (4) speaks of the oases of Arctic vegetation amidst the general barren desert. On the 

 more southerly tundras, however, larger areas are occupied by vegetation than are 

 left unoccupied. The Arctic willows at the base of these mosses represent the first 

 condition ; the overlying sub-Arctic willow, with the accompanying set of plants, 

 represent later sub-arctic conditions. In this district the peat evidently began to form 

 very soon after the passing away of the glaciers and a complete record of the sequence 

 of vegetation is preserved. That the conditions were still severe during the formation 

 of the Salix Arbuscula zone may be inferred from the abundance of this willow over 

 many miles, together with the appearance of many seeds of Arctostaphylos alpina, 

 Lychnis alpina, and patches of Mnium pseudo-punctatuvn. The same story is told by 

 the Empetrum zone lying immediately above. The dominance of Empetrum is very 

 marked here. When pieces of peat from this zone are split open, patches of peat 3 or 

 4 inches across are sometimes entirely covered with the seeds of this plant. In other 

 places patches covered with the seeds of Arctostaphylos alpina are frequent. In the 

 field, this zone is easily recognisable by the abundance of the stems of Empetrum. Over 

 this district, then, three distinct zones are found at the base of the peat, each having 

 its dominant or characteristic plant. The lowest or oldest zone represents high 

 northern tundra conditions ; the second, cold conditions, but not unlike those at present 

 prevailing over the southern region of Greenland ; and the third zone represents a still 

 further amelioration of the climate, for at the base of the third zone Betula nana is 

 abundant, whilst the upper part contains no remains of that plant. 



In the peat lying above these three zones no sign of a return to an Arctic or sub- 

 Arctic flora has been recognised, and none of the plants occurring in the lower Arctic 

 zones are met with. The resemblances of some of these basal beds to plant formations 



