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FENNIA 66, N:o 1
15
these movements were apparently more severe, as may be concluded
from the greater amount of the temporary uplift. Thus, we can say,
that the Ice Age finished in Fennoscandia not only with a deluge, but
also with extraordinarily great earthquakes.
ISOSTATIC RECOVERY.
The presence of elevated marine sediments and raised beaches in
the centre of glaciation was first explained by Jamieson in the year
1865 by means of the theory of isostasy. He considered that the
flexibility of the earth’s crust was so great that it sank beneath the weight
of the land-ice, and so became temporarily submerged, rising again
on the melting of the ice-sheet. According to observations, the
recovery from isostatic depression set in very soon during the removal
of the load. It proceeded at first with relative rapidity, but
ultimately slowed down and will reach its final completion only after a
considerable lapse of time (W. B. Wright 1914, 1937, A. Penck 1922,
R. Daly 1937). Thus, although the recovery in Fennoscandia started
already 12 000 years ago, the recent land upheaval still shows
youthful vigour, as seen above.
Moreover, evidence has been brought forward with a view to
showing that the recovery progressed with a wave-like motion from
the periphery to the centre, the uplift at any stage having always
been considerably more advanced at the periphery than in the centre
(Brögger 1901, Born 1923, Ramsay 1924). This conception, however,
has not been confirmed by the detailed studies of Tanner (1930) in
the northern part of Fennoscandia. In Southern Finland the author
has found, that the changes of level and the uplift of the earth’s crust
have not been controlled in detail by the decreasing ice-load. The
isobases of the late-glacial shore-lines have no definite relation to the
protruding ice-lobes and incisions of the sea between them, as seen
on the map Fig. 5. In fairly good congruence with the curves of the
recent uplift they have their own local course, running in some places
parallel to the ice-border lines, but in other places crossing these, as
for instance within the great eastern ice-lobe of the Salpausselkä
stages. This rule is confirmed by an exception near Lahti, where the
isobases of the late-glacial uplift deviate in some degree from their
recent counterparts and have a tendency to run parallel to the
ice-border. The earth’s crust seems to have had a limit as regards
sensitiveness in the isostatic recovery in detail.
On the whole, however, there is a fairly pronounced relation
between the decreasing ice-sheet and the upheaval of the earth’s crust.
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