55 - ' v * 
- 299 
'V* V ?% 
Fig. 99. Section along the western escarpment of the Krokskogen lava plateau. 
The lavas (P) with their basal Permian sedimentary rocks overlie the folded 
Cambro-Silurian series. The Dranimen granite to the south (right). 
(After Th. Kjerulf 1865.) 
p. 7—24), and he has later presented a comprehensive description of 
the Permian rock complexes and structures of the Oslo graben (Holte- 
dahl 1953, p. 486—556, in Norwegian). 
Together with J. Schetelig, Brogger edited a number of geologic 
maps in scale 1 -.100 000, covering nearly the whole region. 
Unfortunately these maps were never distributed through the 
regular channels, because they were never given descriptions. A survey 
map in scale 1 : 250 000 was printed in 1923 and was issued 10 years 
later (Brogget 1933 a). A map of the surroundings of Oslo (1 :o0 000) 
accompanies the “Guide by Holtedahl and Dons (1957). 
The Oslo region contains irregular areas of Cambro-Silurian 
sedimentare rocks"(Fig. 40), and sedimentary, volcanic, and ptutomc 
rocks of Permian age, see Plate 13. The areal distribution of the more 
important Permian igneous rocks appears from Table 1. The following- 
description is an attempt to present the most important data from a 
comprehensive literature. The rocks are grouped in volcanic, plutomc, 
and dike rocks, and the chapter is concluded with comments on magma 
formation, faulting, etc. 
Permian basal sedimentary rocks. 
The Permian supracrustal rocks of the Oslo region consist of a 
thin series of sedimentary rocks, conformably overlain by a thick series 
of volcanic rocks. Both of these series have been faulted, but not folded. 
The sedimentary rocks are lying on a sub-Permian peneplain, cutting 
various strata of the underlying series of Cambro-Silurian rocks which 
in the northern half of the Oslo region are folded (Fig. 99) while south 
of Dranimen the folding dies out. 
The age of the post-Silurian rocks was not known until 1931 w it a 
Holtedahl discovered fossils in the sedimentary series and these fossiK 
vvere determined to lower Permian age. Fossiliferous strata occur also 
