348 MR FRANCIS J. LEWIS 



at present existing in Greenland will be discussed in the general summary and 

 conclusion. 



As the Empetruin period passed away, the ground became covered with shrubby 

 Betula alba, which forms a continuous and well-marked layer in the peat of this area. 

 The white birch is accompanied by such plants as Menyanthes trifoliata (abundant), 

 (which also occurs in the Empetrum zone, and very sparingly in the Salix Arbuscula 

 zone), Eriophorum, and traces of Calluna vulgaris. This birch zone cannot be 

 correlated with the lower forest zone met with in the Merrick-Kells mosses and in the 

 Tweedsmuir peat of the Southern Uplands (3). The position occupied by the peat and 

 the sequence of the beds above and below the birch zone point to its being a growth of 

 small birch at the beginning of a wet moorland period. Sphagnum and Eriophorum 

 are abundant in this zone, and temperate woodland plants noted in the lower forest zone 

 in the Southern Uplands are wanting (3). 



At the same time the wide occurrence of a shrubby growth of birch above the 

 basal Arctic and sub- Arctic beds over the present watershed, the Findhorn-Nairn water- 

 shed, in Coire Bog and in Caithness, suggests that we are not dealing with a local 

 phenomenon, but with a feature which characterised large areas at the same time. All 

 the evidence, however, shows that the Betula zone here belongs to the wet moorland 

 period which succeeded the primitive Arctic and sub-Arctic conditions. The early 

 occurrence of woodland over these mosses would at first sight seem to imply that a 

 considerable interval must have elapsed after the deposition of the basal Arctic vegeta- 

 tion and before the appearance of the birch. At the time the basal beds began their 

 growth any large area of birch could hardly have existed within several degrees of 

 latitude — if one can judge from the present state of things in Greenland — but only i 

 foot or 1|- feet above this Arctic vegetation we find widespread areas covered with 

 small Betula alba. It must be remembered, however, that we are dealing only with 

 deep peat areas, and in the passage from Arctic through sub-Arctic to temperate 

 conditions these areas would tend to lag behind the drier non-peat covered land. For 

 the cold, water-logged character of the peat would favour the retention of a northern 

 type of vegetation, while it would at the same time exclude many incoming plants of 

 more southernly range, which would otherwise have competed with those already grow- 

 ing over the peat areas. Thus, on the peat-covered tracts, a sub-Arctic type of 

 vegetation might possibly have flourished contemporaneously with the growth of a 

 northern type of woodland over the non-peat-covered lands at a similar elevation. 

 This may explain the invasion of the peat at such an early stage by woodland. It 

 must also be borne in mind that the non-existence of trees over the peat mosses at 

 any one period does not prove that woodland may not have existed elsewhere. All 

 one can say in this connection is, that at one particular time the whole peat areas of 

 Scotland were treeless and covered with a type of wet moorland vegetation and at 

 another time they were wholly covered with forest. It can hardly be questioned that 

 the first represents wet insular conditions ; and the last, drier, warmer, Continental 



