300 
T a b 1 e 1 . 
Principal igneous rock types of the Oslo region and their areal 
distribution (from Barth, 1945, p. 17, with some changes). 
Magma group 
Plutonic rocks 
Extrusive rocks 
Gahbroic 
*Oslo-essexitc» 
km 2 
Basalt and 
km 2 
(Gabbros, kauaiite, 
trachv-basalt 
220 
bojite) 
15 
-Monzonitic 
Kjelsasite 
201 1 
Rhomb porphyries 
1160 
Rarvikite, etc. 
1 705 1 
Tuff 
25 
Trachyte, rhyolite. 
• 
welded tuff, explosion 
Nepheline 
Lardalite to 
65 
vents 
55 
monzonitic 
Foyaite 
to svenitic 
Svenitic 
Alkali syenite. 
Nordmarkite 
1 400 
Granitic 
Kkerite 
821 
» 
Biotite granite 
840 
Sum km 2 
5047 
1460 
between the lowermost lava flows at Holmestrand, indicating that 
also the volcanic activity is of Permian acre. 
The sedimentary rocks show considerable local variation. They 
consist of red and grey sandstones, red shales and a quartz conglom- 
erate. This conglomerate is a very characteristic formation within the 
series. \ yroclastic deposits and sandy tuffitic beds occur in the upper 
part of the series. The most important section is that of Semsvik, Asker, 
where the fossils were found, some 19 km WSW of Oslo. The following 
beds occur, from below: red, sandy shale (not exposed in solid rock): 
conglomerate with 1 — 3 cm pebbles of quartz and quartzite (visible 
thickness 8 m); easily weathered, greenish-grey shale, with sandy 
layers, fossiliferous (5 m) ; grey sandstone overlain by red sandy beds, 
intercalated with conglomeratic beds (10 m). The pebbles of the 
conglomeratic beds consist of basaltic lavas. Then follows the first 
basalt lava. 
The fossils are plants (Hoeg, 1935, 1937 a, b), fresh water mol- 
luscs (Dix and Trueman 1935) and fishes (Heintz 1934). The plant 
fossils belong to the following genera: Catamites , Lebachia, Walchia, 
( ordaites, Neuropteris, and Callipteris, the molluscs to Palceanodonta. 
