3 2o SCIENCE PROGRESS 



Scottish peat mosses. For the purpose of this paper the post- 

 glacial deposits containing arctic plants group themselves into 

 two sets : 



(a) With arctic plants lying between an upper and lower 

 temperate bed. 



(b) With arctic plants at the base overlaid by temperate 

 deposits. 



Type (a) may be considered first. 



At Hoxne, in Suffolk, four distinct superposed strata contain- 

 ing plant remains have been described by a committee appointed 

 by the British Association (6). 



Since the deposits fill a channel eroded through the chalky 

 boulder clay, the intercalated arctic plants must belong to late 

 glacial times, long after the general glaciation of the country. 



The sequence of the beds is as follows : 



i. Brick earth and gravel with temperate plants. 



2. Black earth with arctic plants. 



3. Lignite with temperate plants. 



4. Clay with temperate plants. 



It is sufficient to point out that the basal temperate beds 

 contain such southern forms as Bycopus europcens, Rhamnus 

 frangula, Sparganium ramosam, Sambncus nigra, Rosa cantna, 

 whilst the arctic bed above contains Salix polaris, S. herbacea, 

 S. myrsinites, Betula nana, to show that there is definite evidence 

 in the south of England of a change from temperate to arctic 

 conditions during the later stages of the glacial period. 



Fossiliferous beds of sand and peat yielding some evidence 

 of changes in condition have been described from Ballaugh, in 

 the Isle of Man, by a Committee of the British Association (7). 



In this case the evidence for a change from an arctic to a 

 temperate flora is not so conclusive as at Hoxne. Sandy silt 

 containing Salix herbacea amongst other plants is underlaid by 

 loamy peat and chara marl, from which arctic plants are absent, 

 although most of the plants belong to species of wide distribution. 

 The presence of Apus glacialis in the bed containing Salix 

 herbacea certainly points to colder conditions than the present. 



Numerous sections have been described in which an arctic 

 plant bed occurs at the base of the series overlaid by deposits 

 containing a temperate flora. 



In 1894 Bennie (8) described fossiliferous beds from Hailes, 

 near Edinburgh, the species being determined by Mr. Clement 



