Gh: FLORA ORCADENSIS. 
and Dr Lewis! have accomplished for Caithness and 
Shetland. By means, however, of the results of their 
work in the adjacent counties, we can formulate a 
few conclusions regarding the changes of flora, ot 
climate, and of geographical conditions which must 
have taken place in the extreme north of Scotland 
since the peat began to be formed. We can infer, 
for example, with extreme probability that if the 
vegetation of Caithness or of Shetland at a given 
period was such as flourishes only under arctic or 
sub-arctic conditions, the climate in Orkney also must 
have been severe; and conversely, if trees flourished 
in the north and west of Shetland, there must also 
have been extensive forest growths in the Orkneys. 
Now in Shetland Mr Lewis has found that at the 
base of the peat and resting on the glacial drift 
there is in many places a layer of arctic plants. 
The characteristic members of this flora are Salix 
herbacea and Salix reticulata. This peat sometimes 
lies directly on the boulder-clay, but in other cases 
a layer of aquatic plants occurs beneath it, and 
fragments of Potamogeton, Menyanthes, Ranwneulus, 
and Hqwisetwm underlie the lowest Arctic Bed. 
Pollen grains of Pinus sylvestris have also been 
found below the surface of the boulder-clay. The 
Arctic Bed, however, is the first important and 
widespread formation after the disappearance of the 
glaciers that covered Shetland. 
Above the Arctic Bed there is peat, and at a 
1. J. Lewis, ‘‘ The Plant Remains in the Scottish Peat 
Mosses,” Trans. Roy. Soc. Hdin., vol. xli., p. 699; vol. xlv., p. 335 ; 
vol, xlvi., p. 33; vol. xlvii., p. 793. 
