ON THE PLANT REMAINS IN THE SCOTTISH PEAT MOSSES. 



51 



described, although the basal arctic plant beds in the two districts are not contem- 

 poraneous. 



The lowest arctic bed in Shetland contains the remains of distinctly arctic-alpine 

 plants, and there can be no doubt that this bed was formed under cold conditions soon 

 after the country had been glaciated. 



It is at first very difficult to say whether the basal aquatic vegetation belongs to the 

 same stage as the immediately overlying arctic plants, but the fact that the aquatic 

 plants were only found in a few sections renders it probable that they represent small 



rioph< im 



i na 



Sphag im 



retici ita 

 jtula i na 



•etula 



stula 



retic ,ta 



YW 



Peat formed from aquatic plants 

 underlying the arctic bed. 



Fig. 2. — Diagram showing the general sequence of strata in the Shetland Islands. 



marshy pools which were scattered over the tundra, and therefore actually contem- 

 poraneous with the lower layers of the creeping willow elsewhere in the districts. It is 

 true that such evidence is not conclusive, as the oldest layers of the peat are frequently 

 missing in one part of a district and present in another part of the same district, owing 

 to the peat having begun to grow earlier in one place than in another. Still, there is 

 one feature which makes it extremely probable that the basal aquatic vegetation is 

 really contemporaneous with the arctic bed, and that is the fact that Salix reticulata 

 leaves (not the stems) are occasionally present in the aquatic zone. Very frequently 

 the Salix reticulata bed rests in small hollows in the floor of the moss as shown in fig. 2, 

 in some cases with aquatic plants below, in other cases without. It frequently happens 



