ON THE PLANT REMAINS OF THE SCOTTISH PEAT MOSSES. 



825 



can be made, and when these features are found in places so far apart as the south of 

 Scotland and Shetland the proof seems to me to be conclusive. 



The Upper Forest. — This generally rests upon High Moor peat, formed after the 

 second arctic stage, although in the same districts it frequently runs out on rising 

 ground beyond the High Moor peat and then rests upon drift. This feature is 

 illustrated in fig. 3, which shows a section in the valley between the Merrick and the 

 Kells Mountains in S. Scotland. Similar features occur all over the country, and the 

 pine trees which rest on the drift can be traced into the deeper peat as a continuous 

 stratum. This observation does not prove that pine was not growing on the drift 

 before it spread over the peat at C, but it does show very clearly that after the Upper 

 Forest a period of rapid peat growth took place, when the peat mosses extended their 

 boundaries in all parts of the country. It is possible that this forest represents in the 



Fig. 3. — The Upper Forest at the margin of the deeper peat layers in the Merriek-Kells Mountains. 

 a, Recent peat ; b, Upper Forest ; c, Eriophorum peat ; d, second or upper Arctic bed ; «, Lower Forest ; /, glacial deposits. 



deeper peat areas a true ecological succession, but the fact that it is found over wide 

 areas 1200 feet above the utmost present limit of tree distribution has to be explained. 

 I do not think that edaphic changes can explain such a considerable rise in the 

 altitudinal range of tree distribution. 



Although in Scotland birch and hazel occur in this stratum, pine is the dominant 

 tree, and the accompanying flora is poor and monotonous in character. On Cross Fell 

 in Cumberland (18) the dominant tree of the Upper Forest is birch, which is encountered 

 in the peat mosses up to 2550 feet. From this layer have been collected Ranunculus 

 repens, Lychnis diurna, Ajuga reptans, Elatine hexanolra, Alnus glutinosa, Viburnum 

 Opulus. 



The presence of this flora at 2500 feet suggests warmer and more continental con- 

 ditions, and agrees with the higher level to which trees spread during this period in 

 Scotland. 



TRANS. ROY. SOC. EDIN., VOL. XLVII. PART IV. (NO. 26). 



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