GOHMISSION GEOLOGIQVE - Arkisto.gsf.fi

Suomen Geologinen Seura. N:o 12. Geologiska Sallskapet i Finland. 33
kankara (outcrop 26). In the last-named lodty the whithh quartzite
forms a zone varying from -15 to 20 meters in breadth along the general
strike, sharply bounded by the red quartzite. This variety is more
impure, and a clastic structure is megascopically faintly perceptible,
as clear quartz-gmins are visible embedded in a red mahix. Undeir
the microscope it rnay be seen to contain, besides jroa ore as a h e
pigment and separate grains, rather considerable quantities of siilimanife
of the fibrolite type and scanty scales of sericits. The aillimanite
is arranged, mady along the schistosity, in bunches of minute
fibres showing a brownish aggregate colour, but it &o forms separate
clear fibres. The bulk of the aocewory minerals occupies the interstices
between lenticulrtrly elongated quartz-paina, though oocasionally
fibres of sillimdte h&ve pierced through the grains. The outlines of
the paina are &ged and sutured and grmulated at the margins.
They have been strongly deformed, showing marked strain shadows;
but no regular lattice-orientation is noticeable by meam of a gypsum
plate. The petrofabrics of the Tijriamaa quwtzite will be treated in
a forthcoming memoir by Anna Hietanen.
There appears to be no doubt about the said distinction between
the clear quartz-grains and the more impm matrix representing a
relict clastic textnre of a primary aandstone. The blastoolastic charabcter
of the quartzits is in good harmony with the fact thtct the quartzite
at its boundary is frequently observed to pass over into diatinct conglomerates,
cs will be described below. Still other reliot features of a
primary sedimentary nature rnay be obmrved in the quartzite itself.
In the southwestem wall of the gorge Pirunpesa the quartzite shom
ripple-marka standing almost vertically, but tct an angle of about 16
degrees to the vertical atretching. They have been too poorly preserved
to dow of 8 determination of the stratigraphical position, or the
top side in the stratum. That they have been preserved at all seems
to be due to a certain lamination in the prhary sediment; especially
sericite has been concentrated upon the wavy surfaces. Sericite and
magnetite mostly occur in minute quantities only, but oocasionally
either of them rnay be ooncentnlted in aertain strata. Thus the quartzite
near PPinuipes% contains in places darker layers stained with numerous
magnetite @aina. This is no doubt primary layering.
Vertical jointmgs in directions at right angles to each other are
well developed in the quartzite, one being parallel to the strike and
the other peppendicnlar to it. The gorge of Pirunpesh has been mrved
out along joints in the latter direction.
An analysis of the quartzite from l?irunpesli, Tunsmaa, was exeouted
by Miss Elsa Sthhlberg with the redt quoted below. The Bntc-