Science in Short ChaptersWilliams, W. Mattieu (William Mattieu)
Science
Science in Short Chapters
Williams, W. Mattieu (William Mattieu)
Science
The universality of the terraces in all the Norwegian valleys opening
westward proves a submergence of _at least_ 600 or 700 feet. When I
first visited Norway in 1856, I accepted the usual description of these
as alluvial deposits; was looking for glacial vestiges in the form of
moraines, and thus quite failed to observe the true nature of these
vast accumulations, which was obvious enough when I re-examined them in
the light of more recent information. Some few are alluvial, but they
are exceptional and of minor magnitude. As an example of such alluvial
terraces I may mention those near the mouth of the Romsdal, that are
well seen from the Aak Hotel, and which a Russian prince, or other
soldier merely endowed with military eyes, might easily mistake for
artificial earthworks erected for the defence of the valley.
In this case, as in the others where the terraces are alluvial, the
valley is a narrow one, occupied by a relatively wide river loaded with
recent glacial _débris_. It evidently filled the valley during the
period of glacial recession.
The ordinary wider valleys, with a river that has cut a narrow
channel through the outspread terrace-flats, display a different
formation. Near the mouth of such valleys I have seen cuttings of
more than a hundred feet in depth, through an unbroken terrace of
most characteristic till, with other traces rising above it. This
is the ordinary constitution of the _lower portions_ of most of the
Scandinavian terraces.
These terraces are commonly topped with quite a different stratum,
which at first I regarded as a subsequent alluvial or estuarine
deposit, but further examination suggested another explanation of the
origin of some portions of this superficial stratum, to which I shall
refer hereafter.
Such terraces prove a rise of sea or depression of land, during
the glacial epoch, to the extent of 600 feet as a _minimum_, while
the well-known deposits of Arctic shells at Moel Tryfaen and the
accompanying drift have led Prof. Ramsay to estimate “the probable
amount of submergence during some part of the glacial period at about
2300 feet.”[18]
It would be out of place here to reproduce the data upon which
geologists have based their rather divergent opinions respecting the
actual extent of the submergence of the western coast of North Europe.
All agree that a great submergence occurred, but differ only as to its
extent, their estimates varying between 1,000 and 3,000 feet.
There is one important consideration that must not be overlooked, viz.,
that—if my view of the submarine origin of the till be correct—the
mere submergence of the land at the glacial period does not measure the
difference between the depth of the sea at that and the present time,
seeing that the deposits from the glaciers must have shallowed it very
materially.
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