68 



IT.NIII KSKOI.A. 



M.-X. Kl. 



La.bràdor'ite- rock 



SniiK s|)( ciiiK n> m|' iIk (irhiciil.ir l.ihr.-idMiiic-i-ock from Scljenaes were 

 collected in 1886 In' I >i-. II. Keusch, who cnllefl the rock a pseudoconglo- 

 merate. No microscoitical ( xaminatirin had been undertaken, and the oc- 

 currence has not been niciitioiicd in the liti 1 aliirc. My attention was drawn 

 to these specimens k( pi in tin ( ollections of the Geological Museum ol 

 Christiania, and later I had an opj)ortunity of visiting the locality. 



The r)rbiciilai- labi-adorite-rock occurs in low shore cliffs near the 

 Seljenaes farms at Nordpoll in Siljc. The very best outcrop is a little 

 island calkd Scljenaesholmcn. In the noithern part, next the farm-houses, 

 the main rock is a foliated labradorite-rock of the cr)mnK)n type in this 

 region. It passes oxer into the orbicular \arietv, small rounded lenticular 



nodules appearing in 

 the homogeneous rock. 

 From the ground-mass 

 these nodules first dif- 

 fer only in being ligh- 

 ter in colour, due to 

 the absence of mafic 

 compounds, and in a 

 somewhat finer grain. 

 They may be of the 

 size of peas, but loc- 

 ally they have a long- 

 est diameter of about 

 5 cm. Such larger no- 

 dules often contain mai-garite as their main constituent, and sometimes 

 their inner parts are composed of wollasto n i te. These inner cores ot 

 wollastonite have somewhat irregular forms, and the nodules, though they 

 have smooth surfaces and rounded shapes, do not show any regular con- 

 centric structure. Minerals oi' the epidote group are often abundant. 



The ground-mass always is distinctly foliated, and the whole rock is 

 banded, the size of the nodules in each band or lens being rather invari- 

 able. Lenses of eclogite are commonly enclosed, and they sometimes pass 

 over into the orbicular rock: some nodules appear in typical eclogite, and 

 labradorite gradually replaces the cclogite-constituents. Fig. 10 illustrates 

 an outcrop on Seljenaesholmen, showing lenses of a true eclogite and larger 

 bands of an intermediate type, an eclogitic rock containing nodules of the 

 same kind as those in the labradorite-rock. This eclogite is greatly amphi- 

 bolitized, and may fade over into a schistose amphibolite, rich in biotite 

 and epidote or zoisite. 



The following notes on the microscopic characters do not by any 

 means tend to be exhaustive. It mav be hoped, that this interesting occur- 

 rence will be investigated more in detail. 



The ground-mass of the orbicular labradorite-rock consist of plagioclasc, 

 hornblende and zoisite. 



Fio 



Tli( 



vine-rock 



section in Solvbergknauscn, near Omelfot, 

 Dalstjord, Sondmore. 



