398 PAST succession: the ceneosere. 



Wahnschaffe (1910) assumes that an arctic flora of Dryas, Salix, etc., invaded 

 after the disappearance of the ice. The later loess may be interglacial or 

 late glacial, but the author regards it as late glacial. The climate of the oak 

 period was a maritime one, moist and warm. With Weber and others, Wahn- 

 schaffe regards the horizon-peat as indicating a dry climate which probably 

 came at the end of the lAtorina period. 



Samuelsson (1910 : 197) has re-examined the Scottish peat desposits studied 

 by Lewis, and has made a critical comparison of all the results obtained by 

 investigators in Scotland and Scandinavia. His article is so concise and com- 

 prehensive that no abstract of it will serve the purpose of those specially inter- 

 ested in this field, but his main results may be made available to the general 

 student by means of the tables on page 399. 



Lewis (1911 : 826) has summed up the results of all his investigations of 

 Scottish peat mosses as follows: 



"I described the principal stages, in the history of the vegetation over peat- 

 covered areas since the later stages of the glacial period, in former papers 

 during 1905, 1906, 1907. These stages are as follows: 



1. An arctic-alpine vegetation resting on the moraine laid down by the last mer de 



glace. 



2. A forest of birch and hazel. 



3. A layer of arctic-alpine plants occurring down to sea-level in Shetland. 



4. A forest of pine, hazel, and birch occurring up to 3,200 feet above sea-level. 



5. A layer of peat accumulated from the period of stage 4 to the present day, con- 



sisting entirely of moorland plants. 



" The districts described in this paper amply confirm this sequence. Further 

 investigations in Shetland have shown the existence of the distinct stages of 

 peat growth — one beginning with arctic plants lying on the glacial drift and 

 containing the remains of birch, alder, and rowan, suceeded by a period when 

 alpine-arctic plants again spread over the peat; the other consisting of un- 

 stratified peat formed from moorland plants accumulated during a period 

 when the bogs greatly enlarged their areas, covering the surroimding land. 



"The observations from Rhilochan in East Sutherlandshire show practically 

 the same broad succession for that area, with the addition of an Upper Forest, 

 which, although most widely spread throughout Scotland, has not been found 

 farther north. 



"Special attention has been paid to the character of the two forest beds, 

 and detailed measurements have been made which, as far as they go, prove 

 that the trees occur only at definite horizons in the peat. The fossils collected 

 from the Lower Forest show that the conditions at that time were, as far as 

 temperature is concerned, not markedly different from those of the present 

 day. The Shetland areas, however, show that the forest passed far beyond 

 the present tree limit, and indicate that entirely different meteorological 

 conditions obtained there at that time. 



"The view is taken that the First Arctic Bed, Lower Forest, and Second 

 Arctic Bed represent distinct climatic phases during the early post-glacial 

 stages. The Upper Forest may represent a stage due to edapluc causes, but 

 if this is so it is difficult to account for the existence of this bed so far above 

 the present tree Hmit, unless the trees in that stratum had altogether different 

 ecological requirements from similar species now existing. 



"The view held by Axel Blytt that the forest beds indicate dry periods is 

 not upheld by the plants collected from that layer, although the evidence is 



