704 MR FRANCIS J. LEWIS 
formed. Salix herbacea at the present time is confined to the summits of the highest 
English and Scotch mountains. South of the Tweed it occurs on a few of the highest 
Welsh mountains, and also on the Lake mountains, seldom occurring much below 2500 
feet. In Scotland it is confined to the summits of the Highland mountains, and to a 
few of the summits in the Southern Uplands. S. reticulata is still more restricted in 
distribution, beg confined to the Highlands between 2000-3200 feet. Northwards, 
both plants reach the limits of Arctic vegetation. Extreme northern types are absent 
from the present vegetation of the western part of the Scottish Southern Uplands. 
The basal peat of Section 1 has not yielded any determinable plant remains, 
Microtome sections have been cut and examined under the microscope, when the peat is 
seen to be formed of structureless plant remains, except traces of Sphagnum and some 
isolated pollen grains agreeing closely with those of A/nus glutinosa. The basal layers 
of the peat near Yellow Tomach, however, yield evidence that the conditions about this 
time were not greatly different to those prevailing at the present day. These mosses, 
then, must have originated some considerable time after the disappearance of the local 
glaciers which deposited their moraines between the Merrick and Kells Hills, and at a 
period late enough for the climate to have become not less mild than at the present day. 
At a later date the whole district became clothed with woodland of a fairly northern 
type, mixed with Calluna moor, with a small growth of Sphagnum in the wetter places 
and bordering the moorland pools. After this period the vegetation undergoes a com- 
plete change. The woodland disappears, and the Calluna is replaced by Sphagnum, 
which in turn is again replaced by Eriophorum vaginatum, changes which indicate a 
steady increase in precipitation. ‘l’he Eriophorum zone, later, gives place to an Arctic 
plant-bed consisting of Salix herbacea, S. reticulata, and Hmpetrum mgrum, and thus 
indicating a period when the conditions in the Galloway valleys must have been similar 
to those at present obtaining on the summits of our highest mountains. No other con- 
clusion can, I think, be drawn from this zone, as it maintains its character so uniformly 
over an area many miles in extent, and corresponds closely with the type of vegetation 
covering large areas on tundras at the present time. 
The presence of moraines on the 45-50 feet raised beaches in the Highlands, 
described by Hinxman (5), proves that the smaller moraines found in the Highland 
valleys do not merely represent the dying away of the ice-sheet which deposited its 
moraines in the valleys of the Southern Uplands, but that they belong to a much later 
return to glacial conditions—separated from the former by a period long enough to have 
enabled a temperate flora, represented here by the Betula zone, to have overspread the 
country. If that is so, the Arctic plant zone found in this peat must be contemporaneous 
with this later return to cold conditions—+.e. with the fourth glacial epoch, or the period 
of mountain valley glaciers when the snow-line stood at about 2500 feet. The plant-beds 
above the Arctic zone show a gradual return from cold conditions to somewhat more 
genial conditions, although at first characterised by great precipitation. As the conditions 
became drier, the whole of the valley became covered with pine forest. (Fig. 3.) 
