16 



THE BA.SIC ERUPTIVE EOCKS OF GRAN. 



[Feb. 1894. 



I completed in the summer of 1893 a collection of observations for 

 final publication on the oldest basic series of igneous rocks of the 

 Christiania region, and I have now the honour of laying before 

 this learned Society a resume of the most important results of this 

 detailed investigation on the first eruptive series with which the 

 long sequence of volcanic outbursts in the Christiania region com- 

 menced in Devonian times. 



These oldest eruptions have left a series of interesting plutonic 

 rocks in a number of localities in the parish of Gran, between 50 and 

 60 kilometres (30 to 35 miles) N.N.W. of Christiania, and near 

 Dignses, on Lake Tyrifjord, about 35 kilometres (22 miles) W.N.W. 

 of Christiania. 



Tyj>o, Etching Co. Sc, 



The occurrences in Gran are all situated on a great volcanic 

 fissure-line, in an almost north-and-south direction, parallel with the 

 general direction of the neighbouring Lake Randsfjord, the boundary 

 of the sunken tract in that part of the country. The great fault-lines 

 of Kandsfjord cut the Archaean mass of land at Naes in a south- 

 south-west to east-north-east direction. Only a few kilometres east 

 of this fault-line we find the fissure of the basic eruptions indicated 

 by a series of mostly dome-shaped hills. In order, from north to 

 south, they run as follows : — 



Brandberget (Brandbokampen), 514 metres (1670 feet) above 

 the sea, an imposing hill. 



Subsequently there appear several quite small exposures near 

 Augedal, Solberg, and south of Bilden. 



