60 MR FRANCIS J. LEWIS 



upon the glacial deposits, it represents the arctic flora covering the peat area before the 

 growth of the overlying temperate Lower Forest. The flora is best preserved in 

 Shetland, where the remains of Salix reticulata, S. herbacea x Lapponumif), Betula 

 nana, form a layer about 1 foot in thickness. 



Such creeping Salices occur about 2000 feet on the summits of many of the 

 Highland mountains at the present time, but the conditions in Shetland must then have 

 been entirely different to those which now obtain on our mountain summits ; for below 

 the bed of creeping willow occur many aquatic plants such as Carex ampullacea, 

 Menyanthes trifoliata, Ranunculus repens, Equisetum sps., Viola palustris, Potamo- 

 geton pectinatus. These plants do not occur on the dry wind-swept summits where 

 arctic willows now grow in Britain ; the flora rather suggests an arctic march or tundra 

 with many scattered pools containing an aquatic vegetation. 



This bed so frequently underlying the arctic willow can hardly belong to an earlier 

 stage in the peat history, as the leaves of Salix reticulata are frequently present 

 amongst the aquatic and marsh plants, and have evidently been blown in from the 

 surrounding moorland. The aquatic zone contains much silt, clay, and sand, whilst the 

 bed of creeping willow is entirely free from such deposits. 



After the ice retreated, the ground must have been intersected by numerous rills, 

 streams, and pools, in which grew Equisetum, Potamogeton and Menyanthes. Muddy 

 streams frequently covered this vegetation with fine silt and sand. The drier ground 

 was covered with a close growth of Salix reticulata and other arctic-alpine plants, 

 which, as the pools gradually became silted up, spread over these spots also. Tt is quite 

 evident that the climate of that period allowed a fairly lengthy time for the flowering 

 and ripening of the seeds of such aquatic plants. In fact, the flora indicates a wet cold 

 climate rather than dry conditions with an arctic temperature. Either the First Arctic 

 Bed began to form some time after the disappearance of glacial conditions, or the rise 

 of temperature must have been very rapid during the wane of the glaciers. The rich- 

 ness of the flora indicates that the glacial stage, represented by this bed, was much later 

 than the main ice sheet. 



In a recent account of the development of the Scandinavian flora, Gunnar Andersson 

 (14) records the occurrence of Potamogeton filiformis, P. prselongus, Menyanthes 

 trifoliata, Batrachium confervoides, and other aquatic plants in the Dryas zone, and 

 infers that the Scandinavian climate of that time was not arctic like that, for instance, 

 of North Greenland, but rather resembled South Greenland at the present time. This 

 conclusion is in complete agreement with the features I have found in the N.W. High- 

 lands. The arctic stages appear to mark periods of great precipitation, and these 

 apparently alternated with comparatively dry temperate stages. 



The character of the First Arctic Bed is different in the Outer Hebrides — the only 

 other district in which the peat is old enough to go back to this date. In Lewis, the 

 oldest layer contains Salix Arbuscula, Betula nana, Potentilla Comarum, Empetrum 

 nigrum, Menyanthes trifoliata, Potamogeton sps. 



