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If we draw a line along the Hardangerfjord and continue it
eastward to Lake Mjøsen, we have on its southern side a great Archaean
region in which gneiss and foliated granite are prevalent rocks.
Telemarken is a province in southern Norway. A peculiar
series of Archaean rocks, the Telemarken series, occurs in it and
in the adjacent region to the north of it. Many of the rocks
here are obviously clastic such as conglomerates, sandstones and
clayslates, but besides these rocks crystalline schists as gneiss,
granulite, hornblende schist also occur. The strata are folded and
often traversed by granitic dykes.
Kongsberg «the King’s mountain» is a celebrated mining town
about two hundred and fifty years old, one of the few places in
the world where native silver is the chief ore. The silver, which
sometimes occurs in good crystals, besides other minerals, has
made the mine well known among mineralogists. A peculiar
relation existing between the ore in the veins and the «country» rock
has been a puzzle to the students of ore-deposits for more than
a century. The region consists of vertical strata, striking north
and south, of gneiss, quartz schists and mica schists. In two
bands lying in the line of stratification, the rocks contain grains
and small patches of pyrites and other sulphurets. The rocks
assume a rusty appearance where the pyrites occurs, and the
bands can by that character be followed on the surface without
difficulty. The silver-bearing veins run across the stratification
in an east and west direction. The veins are vertical fissures
filled with different minerals, chiefly calcite. The silver occurs in
paying quantities only where the veins intersect the
pyrites-bearing bands of the «country» rock. No satisfactory explanation
has as yet been given for this remarkable fact. It has been
suggested that the pyrites increases the electric conductivity of
the rock and that currents of electricity passing through these
bands have precipitated the silver from solutions circulating in
the fissures, which have become the veins.
A great Norite region occurs in the vicinity of Ekersund in
the south-west. Some varieties contain titaniferous iron-ore as a
constituent and in a few places such ore is concentrated to
dyke-like or vein-like masses which have been worked for mining
purposes. From a theoretical point of view this occurrence has been
of interest as showing an instance of ore-deposits formed in an
eruptive way by differentiation within an eruptive mass.
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