ON THE PLANT KEMA1NS IN THE SCOTTISH PEAT MOSSES. 



47 



peat, overlaid by birch, and in other places the birch itself occurs at the base of the peat, 

 the older beds being wanting. Peat-formation would hardly begin simultaneously over 

 so large an area as this, and we should expect to find some areas dating back farther 

 than others. Details of two sections will serve to illustrate this point and to give the 

 general sequence over this area : — 



Section I. : — 



Characteristic Plants. 



1. Scirpus csespitosus. 



2. Betula alba. 



3. Erica cinera. 



Section II. 



Accompanying Plants. 



1. Sphagnum. 



2. Corylus A vellana. 

 Alnus glutinosa. 



3. Emjpetrum nigrum (traces). 

 Eriophorum vaginatum (scarce). 



Fine sand and rock. 



Characteristic Plants. 



Accompanying Plants. 



1. Scirpus csespitosus. 



2. Calluna vulgaris. 



3. Sphagnum. 



4. Betula alba. 



5. Salix Arbuscula. 



1. Sphagnum. 



2. - 



3. Scirpus csespitosus. 



4. Scirpus ccespitosus. 



5. Empetrum nigrum, 

 Viola palustris. 

 Carex sp. 



The younger layers of peat resemble those in Skye, but the basal beds of Salix 

 Arbuscula, Empetrum and Carices, carry the history a stage further back. Section II. 

 shows the more general sequence, where a thick bed of creeping willow occurs at the 

 base of the peat. This type of vegetation does not now form a continuous sheet in any 

 of the Outer Hebrides, or at similar altitudes anywhere in Britain, being confined to 

 mountainous regions. The Betula alba zone consists of fairly large trees, mixed in 

 some places with Corylus Avellana and Alnus glutinosa. The persistence of this zone 

 in nearly all the sections, combined with other features to be described later, suggests 

 that it represents the lower forest, and this correlation is supported by evidence from 

 Shetland. The upper layers of peat in this district contain no trace of forest, and in 

 this respect they agree with the mosses in Skye and N. Uist. 



(b) Peat South of Barvas and the Bragor River Basin. — The peat along the west 

 coast has been much dug for fuel by the inhabitants of the numerous crofting villages. 

 In some places the peat runs almost to the coast, in others there is a narrow fringe of 

 poorly-cultivated ground a mile or so in width, protected from the sea in the neighbour- 

 hood of Barvas by extensive sand-dunes. Eound the crofting villages of Barvas, Arnol, 

 and Bragor, the peat has been entirely carried away for fuel, laying bare the gneiss, 

 on which little or no vegetation manages to find a hold. Over other large areas the 

 upper layers of peat have been removed, leaving a waste of crumbling black peat which 

 does not support any vegetation. Probably all the cultivated areas have originally been 

 covered with peat ; as the turbaries are exhausted and the underlying rock reached, a 



