Full resolution (JPEG) - On this page / på denna sida - First part - I. Physical Geography - 3. Geology. By E. Erdmann, Ph. D., State geologist, Stockholm
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
48
I. PHYSICAL GEOGRAPHY OF SWEDEN.
When, after thousands of years, the cold had passed its climax,
and an improvement in the temperature set in, the ice-fields began to
retreat and finally became restricted to the central, highest parts of the
Scandinavian peninsula; but on the ice-worn surfaces of röck there
was left an extensive deposit of moraine-detritus consisting of earthy,
sandy, or clayey material, more or less charged with stones of all sizes.
This material had been carried underneath, within or on the surface
of the ice-fields and glaciers. In Sweden such moraine-material, >fiJZ>
and >boulder-clay>, is the most extensively spread and the most common
of all Quaternary deposits. By far the greater part of the
forest-bearing tracts as well as of the slopes of hills and highland mountains
consist of this material. When the moraine-material is derived from
soft rocks, as for instance Silurian clay-slates and limestones, it is
clayey and calcareous (boulder-clay, moraine-clay, moraine-marl) and
makes good arable land. The fertile plains of Skåne consist chiefly
of such calcareous boulderclay.
Another kind of deposits, formed in close connection with the
melting away of the ice in our country, are the remarkable ridges of
sand, rounded gravel, and pebbles which are called åsar (kames). They
are supposed to have been formed by glacier-rivers, which, running
under the ice, found their way from the interior of the ice-fields towards
the ice-border, making tunnel-like passages in the ice and depositing
the material carried along — pebbles, coarser and finer gravel and
sand — near the outlet, as the current grew less strong. Ridges of this
kind occur in almost all parts of the country, where they often run
continuously for many miles, at a distance of a few to twenty
kilometers from each other, sometimes rising to a height of 30 to 50 meters.
A part of the city of Stockholm is built on one of these ridges.
Sometimes one dominant ridge is joined by tributary ridges, just as a river
by its affluents.
At the end of the Glacial period, when the great land-ice was
in process of recession, Sweden was partly submerged under the sea.
Gotland and Öland were altogether covered by this Glacial ocean,
and so were the provinces round lake Mälaren as well as the greater
part of Östergötland. The surroundings of lake Venern were also
submerged to an extent of 140 to 180 meters, and the Western ocean joined
what is now the Baltic by a broad strait across Nerike. On this submerged
territory, sediment, carried out by the glacial streams, was deposited,
forming the often beautifully stratified clay, glacial-clay, which is now
found extending over our largest plains as well as in valleys. In several
places it contains shells of the little arctic bivalve, Yoldia arctica, and
remains of other arctic animals corresponding to those now living in
the ocean near Spitzbergen and Greenland. Where the clay has been
washed out of calcareous moraine-material, that is to say on and south
of the Silurian and the Cretaceous territories, it is more or less cal-
<< prev. page << föreg. sida << >> nästa sida >> next page >>
