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- Geology, by H. H. Reusch
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CAMBRIAN, SILURIAN AND DEVONIAN.
We can form only very uncertain opinions about the
condition of the earth during the first long division of its history,
the Archaean period. The oldest remains of organic life have
been preserved in the rocks formed during the Cambrian period
and from that time, we may, as we all know, follow the history
of life until the present time. In Norway we possess the oldest
fossiliferous strata, but only up to the Devonian. Then a great
gap follows, with only a single small patch of Jurassic strata, until
the quite recent deposits of the Ice Age.
During Cambrian and Silurian time the open sea extended
over the greater part of Norway. On the bottom of that sea,
lime, mud, sand and gravel were laid down forming a series of
strata attaining a great thickness. The organic remains therein
are of invertebrate animals, graptolites, trilobites, corals and upon
the whole showing the general characters which the fossils of
these old deposits show everywhere.
The oldest deposits are called in Norway the Sparagmite
formation, after the prevailing rock. The Sparagmite is a
felspar-bearing [[** sjk bindestrek]] sandstone, consequently the name corresponds somewhat
to the word Arcose often used in the geological literature of other
countries.
Strata of Sparagmite of enormous thickness and but little
disturbed, form a great portion of the rather monotonous region
in the interior of Southern Norway to the north of Kristiania
(Sp on the map).
The tract between Lake Mjøsen and the little
Langesundsfjord is called the Kristiania region. The interior consists
of Post-Silurian eruptive rocks which are covered with forests.
These eruptives exhibit a long and remarkable series of granular,
crystalline, granitic and syenitic rocks and of porphyries. The
eruptives are fringed by Cambro-Silurian strata. Sandstone is
present here only to a very small extent, while clay-slate and
limestone are the prevalent rocks often abounding with fossils.
The rocks weather easily and we find here some of the best soils
in Norway. The beautiful hilly country and the smiling islands
in the immediate neighbourhood of the capital have this formation
as their sub-soil.
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