X¢Cll FLORA ORCADENSIS. 
oped in the most exposed situations as in the valleys. 
The plants are all such as might commonly occur in 
a swampy deciduous wood in any part of southern 
Great Britain at the present time. 
The Forest Bed is sometimes two feet or more in 
thickness, and is overlain by a layer of peat con- 
taining Hriophorum and Sphagnum. This is followed 
in turn by a second Arctic Bed a few inches thick. 
It occurs in nearly all the localities where the peat of 
Shetland has been investigated. Salia herbacea and 
Betula nana are found in this layer, but Betwla 
verrucosa has now completely disappeared. This 
flora indicates that the climate had certainly under- 
gone a change for the worse. The entire absence of 
the temperate plants of the Forest Bed can hardly 
be otherwise explained. 
Above the second Arctic Bed there is peat formed 
of Scirpus, Eriophorum, Sphagnum, and Calluna. 
It is not stratified as a rule, and may be many feet 
thick. Sometimes this layer rests directly on a 
weathered surface of boulder clay, and there seems 
reason to believe that in such cases the older peat 
deposits had been eroded away, or the conditions 
may have been unsuitable for the accumulation of 
plant remains, before the upper peat was deposited. 
In Foula, in the upper peat, a layer was discovered 
very rich in fragments of Juniperus communis. Its 
exact significance is doubtful, but Mr Lewis points 
out that it corresponds in position with the Upper 
Forest Bed of the mainland of Scotland, of which 
the characteristic tree is Pinus sylvestros. 
Dr Crampton, as the result of a wide survey of 
