I'KN'ITI KSKOI.A. M.-N. Kl. 



(in hiuli \<>ll schrcihc-n ohne dabei klüger zu werden; d<nn die wahre 

 (iiundlage ii'w dii- Diskussion fehlt, solange man sicii in der jetzigen 



Unwissenheit iih» i di« l>ildun,i; d« |- krystailinen Schiefer befindet. Wenn 

 es sich \i(ll( i(ht < iiniial herausstellen wii'd, das.s dieselbe von derjenigen 

 dci- älleicn l'juptivgesteine nicht so weit verschieden sei, dann dürften 

 Gesteine wie die krystallinischen Olivin.schiefer vielleicht auch leichter zu 

 verdauen sein." 



At present we regard the gneiss as an intrusive rock. The conclu- 

 sions of the first Norwegian investigators nevertheless are wholly valid as 

 regards the close connection of the olivine-rocks with the gneiss. Both 

 have the same mode of origin and both are igneous rocks with a primary 

 mineral com]5osition. 



As evidences of the primai-y, non-m(tamor[)hic character of the olivine- 

 rock we may name the absence of every relict feature, and the .structure 

 of the varieties containing other minerals than olivine: they are true 

 igneous differentiates apparently originated by the crystallization of their 

 actual minerals. 



This ol i \- i n e-rock is an igneous rock, a d u n i t e. It is a 

 member of the Norwegian peridotites, on which C. W. Carstens • recently 

 started a series of investigations. 



The olivine-rocks are not younger than their country-rock, their con- 

 solidation has taken place rather earlier, but there is probably no great 

 difference in age. This interpretation of the genetical relations holds good 

 no matter whether the gneiss-formation is regarded as being of Archaean 

 or of post-Archaean age. 



F^or the earlier inx'estigators the conformable stratigraphy and the 

 absence of evidences of intrusion were the most weighty arguments in 

 favour of a common origin of the gneiss and the olivine-rock. From the 

 present stand-point, regarding the rocks as a series of magmatic differen- 

 tiates, these proofs are not quite sufficient, as many intrusive masses also 

 show conformable boundaries and absence of intersecting veins, enclosed 

 fragments etc. For me the decisive evidence lies in the protoclastic or 

 primarily foliated character of the whole gneiss formation. Thus, when 

 the olivine-rock allots itself to the same unit, its intrusion and foliation 

 prove to be results of the same process of folding and intrusion. Later 

 we shall pay attention to the evident connection of the olivine-rocks with 

 the eclogites, and it will appear that both kinds of inclusions are of an 

 earlier consolidation than the gneiss. 



The olivine-rock in Al m kl o vd al en, Vanelven, Sendmore. 

 A pétrographie description of the olivine-rock of Almklovdalen was given 

 by W. C. Brøgger (loc. cit., 1880). The rock of this locality is, for the 

 greater part, a very pure and unaltered oli\-ine-rock 6f even and medium 



' C. W. Carstens, Norske peridotilcr, I and II. Norsk Geologisk Tidsskrift, V, 1918. 



