18 TEOF. W. C. BEoGGER ON THE [Feb. 1894, 



A more considerable occurrence, Solvsberget, is tbere met with 

 (0 kilometres or 5g miles south of Brandberget), a fine eminence, 

 484 metres (1575 feet) in height. 



Four kilometres (2| miles) south of Solvsberget we find the two 

 hills of ' Viksfjeldene' (the Vik mountains), Kjekshushougen and 

 Buhammeren, 537 and 538 metres (1745 & 1749 feet) respectively- 

 above the sea-level. 



The occurrence at Dignoes, on Lake Tyrifjord, is about 40 kilo- 

 metres (25 miles) south-west of Buhammeren. 



The plutonic rocks in each and all of these localities are closely 

 connected by numerous passage-types, and present a wholly con- 

 tinuous series of basic abyssal rocks. It seems, therefore, impossible 

 to doubt that all these rocks, so closely allied in composition 

 and geological occurrence, have originated from a common source. 

 The limited time at my disposal allows only of a very summary 

 description of the principal varieties. 



II. The Olivine-Gabbeo-Diabases. 



The prevailing kinds of rock in all the greater occurrences (Brand- 

 berget, Solvsberget, Viksfjeldene, and Dignass) we may characterize 

 as olivine-gabbro-diabases. They are medium- or coarse-grained 

 rocks of granitic structure, often also ophitic ; there is not the 

 slightest trace of the ordinary changes met with in regionally meta- 

 morphosed gabbro. The mineral composition is, firstly, plagioclase, 

 the constitution of which varies, mainly from AbjAnj to Ab An., 

 and consequently it belongs to the labradorite series ; quite sub- 

 ordinate, a small proportion of orthoclase is also proved to occur in 

 several specimens (in the main rock of Solvsberget it is very 

 common). Besides the felspar a mineral of the pyroxene group 

 prevails : the common pyroxene in these rocks is a violet, tita- 

 niferous, lime-magnesia-pyroxene, with comparatively small amounts 

 of aluminium- and iron-oxides ; olivine and a dark reddish-brown 

 biotite (lepidornelane) are both common constituents. An ortho- 

 rhombic pyroxene (bronzite or hypersthene) is observed in the 

 rock of Solvsberget, but in very small quantities. Basaltic brown 

 hornblende is rarely present, and then in small quantity. The 

 common iron ores, titanic iron and magnetite, in small amounts, 

 also pyrite, pyrrhotite, and apatite, the last often abundant, make 

 up the rest of the primary components. 



A detailed petrographical description of the varieties of the 

 olivine-gabbro-diabase in the different localities, and, still more, a 

 thorough study of all the facies-types, would carry us too far. I 

 shall therefore, on this occasion, confine myself to pointing out the 

 important circumstance that the prevailing rocks in the different 

 exposures along the fissure clearly change their character in a 

 regular manner from north to south. On the whole, the average 

 basicity of the prevalent rocks can be proved to decrease in that 

 direction. 



