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GEOLOGY.
53
the whole Paleozoic era and the first part of the Mesozoic. It is probable that
the formation of the Scandinavian mountain range in its principal part was
commenced and gradually completed in conjunction with the very rise of the
land above spoken of, which itself may have taken an immense time.
Meantime there were all the while many various agents at work reshaping and
gradually readjusting the surface conditions of the ground, such as weathering,
rain and flowing water, etc. River valleys were hollowed out here and widened
there, fjeld plateaus and mountain crests were degraded and finally removed,
and in a very large part of the region formerly covered by the comparatively
speaking loose rocks of the Silurian System, that did not offer much resistance,
those strata were destroyed or, as one might say, swept away.
From a practical point of view the Cambrian-Silurian rocks with normal facies
are of very great importance. In the southern part of the island of Gottland
there is quarried an Upper Silurian sandstone, light-grey in colour and easy to
work, that has been made a great deal of use of in architecture. The
well-known Gottland grindstones for instance are made of that material.
Lower Silurian limestone (orthoceras limestone), both ruddy brown and grey,
are utilized as building and facing stones, as material for mouldings, for stairs
and floors, and for architectural ornaments; extensive quarries of it exist in
Närke, in Västergötland, in Östergötland, on the west side of the island of
Öland, in Skåne, in Dalarne, and in Jämtland. Of the varieties of Upper Silurian
limestone occurring in Gottland there are several that are very much used for
architectural purposes; members of the medieval church porches in Gottland
being built of it; in many cases they are very well preserved. In several
localities in Västergötland and Närke bituminous limestone is quarried and used
for the production of lime by burning; in this process bituminous alum-shale,
which is quarried at the same time as the limestone, is made use of as fuel;
formerly the burnt alum-shale was utilized as the raw material for the
production of alum.
Only in Skåne are there deposits of systems of strata younger than the
Silurian, viz. of the Trias, the Jurassic and the Cretaceous Systems, as
well as, to a small extent, of the Tertiary.
The Trias System. There are to be found developed in Skåne those
strata of this system that are classified as constituting its younger group,
Keuper; they consist of brownish red and greenish or else mottled clays,
marls and sandstones and also conglomerates. These form the rock-floor
in three small areas in the north-west of the province.
The Keuper strata also extend beneath the Rhæt-Lias, the formation next
younger in age, lying themselves over and in immediate contact with the
Silurian, as has been shown by numbers of deep borings. The thickness of the
Keuper-förmation in Skåne may be put down at 200 meters. There are no
coal-seams in the Keuper of Skåne.
In conjunction with the Skåne Keuper there should be mentioned a sequence
of strata, up to 300 meters thick, of sandstones, schists and slates etc. These
deposits are named the Visingsö Series, being found on the Island of Visingsö
in Lake Vättern, and also cropping out at several places on the shores of that
lake. No fossils have been discovered in this sequence of strata, and its age
must still be left an open question. The strata were thrown down in the basin
of Lake Vättern by faults running north and south and have thus been protected
from denudation.
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