ON THE PLANT REMAINS OF THE SCOTTISH PEAT MOSSES. 809 



entirel)- different meteorological conditions from those occurring at present, i.e. the 

 frequent very strong gales which now pass across these islands must then have been 

 absent. It is also possible that considerable elevation of the land-surface took place in 

 early post-glacial times. This view is discussed on p. 821. 



The Second Arctic Stratum in Shetland. — This stratum is nearly always present 

 above the Lower Forest. In some places in W. Shetland, however, it cannot be dis- 

 tinguished from the Lower Peat Bog and the overlying peat, the stratum in those cases 

 being formed of peat bog plants such as Potentilla Comarum, P. tormentilla, and 

 Menyanthes trifoliata. Where the stratum is well developed Salix herbacea and 

 Betula nana are present in some abundance. 



There is no doubt that at this time Betula verrucosa, Ehrh., had entirely disappeared 

 from all the peat areas in Shetland. The question arises as to how far the arctic plants 

 generally found here indicate a distinct lowering of the temperature. My own view 

 is that this bed does indicate such a change ; but the possibility that these plants, which 

 must have formed small colonies on the hill summits during the Lower Forest stage, 

 may have reinvaded the peat areas without a distinct lowering of the temperature, 

 must be borne in mind. How far they would be able to recolonise peat occupied by a 

 close sward of vegetation is doubtful, but there is no evidence on this point. In view, 

 however, of the general distribution of this stratum in Scotland, the evidence, I think, 

 points to the intercalation of a distinct period of sub-arctic conditions at this time. 

 Certainly none of the temperate plants of the forest bed occur at this level. 



2. Poolewe, Ross-shire. 



(One-inch Ordnance Survey, sheet 91). — The areas examined lie west and north-west 

 of the village of Poolewe, on a broad peninsula running 7 miles from the village to the 

 norfch-west. The centre of the peninsula lies at an average altitude of over 900 feet, and 

 is almost entirely covered with peat. The surface of the ground is very hummocked, 

 with the peat lying in basins, sometimes only a few hundred yards across, surrounded 

 by rock ridges and hummocks which may rise 20-100 feet above the level of the peat. 

 The usual depth of the peat is 6 feet, except in one or two spots, which from the char- 

 acter of the deposits, occupy the sites of silted-up lochs. 



The peat contains no strata with alpine or arctic plants, and began its growth during 

 the Upper Peat Bog stage immediately preceding the Upper Forestian (3). Sections 

 taken near Loch Tollie at an altitude of 400 feet showed the following layers : — 



A. Scirpus- Sphagnum ........ 3 feet. 



B. Pinus sylvestris . . . . . . . . 2^ „ 



C. Equisetum 6 inches. 



Boulders and sand. 



A. Most of this layer is formed of Scirpus csespitosus, Sphagnum sp., Eriophorum 

 vaginatum, Erica Tetralix, with a few seeds of Drosera sp. and Narthecium ossifragum, 

 TRANS. ROY. SOC. EDIN., VOL. XL VII. PART IV. (NO. 26). 118 



