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Suomen Geologinen Seura. N: 0 35. Geologiska Sällskapet i Finland. 85
is 600 km long, and that the destructive work of that earthquake could be
followed along a line of more than 400 km (Wahl 1917).
Outside this strip, hypersthene granodiorites have been described by
Hackman (1923) from the islands of Kakskerta and Kustö, about 15 km
southward from Abo (Turku) in SW Finland (»charnockite»). Further,
Laitakari (1942) has described pyroxene diorite containing hypersthene from
Lill-Kyro (Vähäkyrö), east of Vasa. Parras (1958) has described a fairly
large district of charnockitic rocks from the northwestern part of the province
of Nyland (Uusimaa), the centre of this district being ab out 50 km
NW of Helsingfors (Helsinki). The occurrence of hypersthene in trondhjemite
NE of Abo has also been mentioned by Huhma (1959).
From Ojanperä in the parish of Paavola (Raahe), Nykänen (1959) has
recently described a small district of coarse-grained granodiorite containing
hypersthene. This occurrence is inside the 100 X 450 km strip of rocks dealt
with here.
As we have seen, there are in Finland outside the belt of hypersthene
rocks mentioned only four occurrences of hypersthene rocks. The principal
ones are the charnockite and paracharnockite districts described by Parras
(1958), the charnockite district described by Hackman (1923) and the two
other small occurrences referred to here.
In contrast, inside the belt, from Ladoga to the northern part of the
Bothnian Gulf, there are about 60 localities where hypersthene rocks of the
peculiar brown colour occur. The thin section collection of the Geological
Survey of Finland contains ab out 70 sections of these rocks, and six analyses
of the hypersthene rocks have been made. It is also noteworthy that several
of these occurrences are rock bodies of considerable size: thus the occurrence
NW of Savonlinna is about 5 X 20 km, the occurrence of Rautalampi about
6 X 25 km, the occurrence of Konnevesi about 10 X 8 km, the occurrence of
Viitasaari about 4 X 12 km and the occurrence of Kiuruvesi about 8 X 17 km,
and there is further the large occurr€mce in southern Kangaslampi, which
continues southward across the islands between Äänisvesi and Haukivesi,
being mostly covered by the lakes.
The rocks of the large district of hypersthene rocks in southern Nyland
described by Parras (1958) and mentioned above are, however, probabiy
not original igneous rocks, but have through later transformations changed
to hypersthene rocks, that is »charnockites». The hypersthene rocks of
Central Finland are, as clearly indicated by many circumstances with regard
to their mode of eruption, their contacts and the apophyses and dykes they
send into surrounding rocks, to be considered as pr im ar i I y i g neo u s
r 0 c k s. They have thus nothing in common with the »charnockites» with
regard to origin, and they are therefore not comparable to what are now
generally considered as »charnockites», which recently have been dealt with