3 i2 SCIENCE PROGRESS 



The First Arctic Bed. — This bed has so far only been met 

 in the Outer Hebrides and the Shetland Islands. Occurring 

 at the base of all the beds and resting upon the glacial deposits 

 it represents the arctic flora covering the peat areas 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 Lapponum, Bctula nana form a layer 

 of closely compressed peat about i ft. in thickness. 



Such creeping Salices occur on the summits of many of 

 the Highland mountains above 2,000 ft. 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, Potamogeton 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 marsh 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 any 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. It is quite 

 evident that the climate of that period allowed a fairly lengthy 

 time for the flowering and ripening of the seeds of these 

 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 dis- 

 appearance of glacial conditions or the rise of temperature 

 must have been very rapid during the wane of the glaciers. 

 The richness of the flora indicates that the glacial stage, 



