A similar succession of deposits is met with in the valley of the
Forth,[CT] and we cannot doubt that these tell precisely the same tale.
I have elsewhere[CU] adduced evidence to show that the peat-bed, with
drifted vegetable débris, which underlies the Carse accumulations of
the Forth and Tay is on the same horizon as the "lower buried forest"
of our oldest peat-bogs, and the similar bogs that occur in Norway,
Sweden, Denmark, Schleswig-Holstein, Holland, etc. Underneath the
"lower buried forest" of those regions occur now and again freshwater
clays, charged with the relics of an arctic-alpine flora; and quite
recently similar plant remains have been detected in old alluvia at
Corstorphine, near Edinburgh. When the beds below our older peat-bogs
are more carefully examined, traces of that old arctic flora will
doubtless be met with in many other parts of these islands. It was
this flora that clothed north-western Europe during the decay of the
last district ice-sheets of Britain and the disappearance of the great
Baltic glacier.
[CT] _Proc. Roy. Soc. Edin._ 1883-84, p. 745; _Mem. Geol. Survey,
Scotland_, Explanation of Sheet 31.
[CU] _Prehistoric Europe_, chaps. xvi., xvii.
The dissolution of the large valley-glaciers of this country was
accompanied by a general retreat of the sea--all the evidence leading
to the conviction that our islands eventually became united to the
Continent. The climatic conditions, as evidenced by the flora of the
"lower buried forest," were decidedly temperate--probably even more
genial than they are now, for the forests attained at that time a much
greater horizontal and vertical range. This epoch of mild climate and
continental connection was eventually succeeded by one of submergence,
accompanied by colder conditions. Britain was again insulated--the
sea-level in Scotland reaching a height of 45-50 feet above present
high-water. To this epoch pertain the Carse-clays of the Forth and Tay.
A few erratics occur in these deposits, probably betokening the action
of floating ice, but the beds more closely resemble the modern alluvial
silts of our estuaries than the tenacious clays of the 100-feet
terrace. When the Carse-clays are followed inland, however, they pass
into coarse river-gravel and shingle, forming a well-marked high-level
alluvial terrace of much the same character as the yet higher-level
fluviatile terrace which is associated in like manner with the marine
deposits of the 100-feet beach.
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