Full resolution (JPEG) - On this page / på denna sida - Geology, by H. H. Reusch
<< 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 been proofread at least once.
(diff)
(history)
Denna sida har korrekturlästs minst en gång.
(skillnad)
(historik)
volcanic ashes and lava-streams. The rocks are principally
finegrained and more or less schistose rocks of a greenish colour due
to the presence of chlorite or hornblende in microscopical or
almost microscopical grains. Acid tuffs may also have been thrown
out of the ancient volcanoes, but it is more difficult to point out
rocks which have been formed of these. Deep seated eruptives
occur as metamorphic granite and gabbro, also a great number of
dykes altered by pressure. The ordinary sedimentary deposits
interstratified with the volcanic rocks show by their nature that they,
as a rule, have been formed in shallow water. Beds of
conglomerate attain considerable thickness. The clay-slate has in several
areas been converted into mica schists. Limestone, which is
generally altered into marble is often interstratified with the schists.
Fossils are found in some places in the Trondhjem region. They
belong to the upper part of the Cambrian and to the Silurian,
but these fossilbearing localities are too few to give us more than
a very limited account of the succession of rocks in this great
area. Fossils are also found at very few places in the altered
Cambro-Silurian of the western part of Southern Norway.
The Cambro-Silurian northwards from the Trondhjem region
is even less known. Some few traces of crinoid stems have been
found. Beds of limestone and dolomite attaining considerable
thickness occur in some places on the coast of Northern Norway.
These deposits are now beginning to be worked for marble, and
it is hoped that an industry of considerable importance may develop.
Some very pretty varieties consist of pressed conglomerates of
limestone fragments showing different shades of red.
Some interesting ore-deposits occur in the region described.
They consist of pyrites sometimes containing a small percentage
of copper, making it valuable as a copper ore. The Røros
coppermine has been worked for two hundred years, while Sulitjelma
coppermine (somewhat north of the Polar circle) has been worked
only a few years but has developed quickly. The ores occur as
rather pure lenticular masses in schists. These masses attain such
a very great length in proportion to their thickness that they
assume the form of sedimentary strata and they have even been
regarded by several geologists as having been formed by some
sort of sedimentation in a similar way to bog iron ore. But it
has been pointed out, on the other hand, that they always occur
in the immediate neighbourhood of masses of altered gabbro. They
<< prev. page << föreg. sida << >> nästa sida >> next page >>
