42 MR FRANCIS J. LEWIS 



III. Near Slidderies Burn at 2250 feet : — 



Characteristic Plants. 



1. Kriophorum vaginatum. 



2. Calluna vulgaris. 



3. Potentilla Comarum. 



4. B'-tnla alha (large). 



5. Salix reticulata, S. Arbuscula. 



Accompanying Plants. 



1. Calluna vulgaris. 

 2. 



3. Salix Arbuscula. 



4. Viola palustris, Ajuga reptans. 



5. Equisetum sps., Carex sps., Sedum Rhodiola. 

 Boulder clay. 



These three types are instructive, inasmuch as they show that peat of very different 

 age may be encountered in dealing with a large district. 



In Section III. arctic vegetation occurs at the base of the peat resting upon boulder 

 clay, but this is not the case in Sections I. and II., which are evidently younger than the 

 third type. 



In Section III. Betula alba with Viola palustris and Ajuga reptans overlies the 

 basal arctic vegetation ; in Sections I. and II. a similar vegetation occurs at the base 

 of the peat. 



The remaining beds in the three sections show remarkable agreement in their main 

 features, but they exhibit particularly interesting features in connection with the upper 

 forest. The upper forest is, in this district, as in so many others in the Highland areas, 

 in two distinct zones separated by about 2 feet of peat. The upper tier in Section I. is 

 composed of pine and the lower of birch. The peat between shows a very different kind 

 of vegetation , such plants as Salix Arbuscula, Potentilla Comarum, Betula nana, Carex 

 sps., replacing the birch and pine. The intercalation of such arctic or sub-arctic plants 

 between the two layers of the upper forest is not confined to the Grampians, as it also 

 occurs in Caithness and Sutherland. The lower tier of forest forms a good datum line, 

 as it is present in all three types of mosses. The intercalated arctic plants above are 

 also present in the first and third type, whilst in the second a zone of structureless peat 

 occurs at this horizon. In the second and third type the upper tier of forest is wanting, 

 but in both cases a bed formed almost entirely of Calluna stems occurs at the same level 

 in the peat. 



The presence of intercalated arctic or sub-arctic vegetation seems to give strong support 

 to the view that there was a change of conditions between the growth of the lower and 

 upper tier of the last forest period. At the present clay such plants as Salix Arbuscula, 

 Betula nana, do not form moors at the same elevation and under the same climatic 

 conditions as a forest of pine or birch. The observations of W. G. Smith (4) upon areas 

 bordering the one under consideration show that the birch forest and accompanying 

 vegetation extends up to about 1500-1750 feet, whilst the highest moors at 2000-3000 

 feet are dominated by an association formed of Calluna and Vaccinium M:urtillus with 

 Cornus Suecica, Rubus Chamsemorus, Betula nana, Lycopodium annotinum, Loise- 

 leuria procumbent. In addition to this it should be remembered that most of the woods 

 occurring so high as 1750 feet are of small extent and have clearly been planted, and all 

 of them are protected either by dry stone walls or by some natural feature ; and as far 



