lOO 



I'KNIII KSKOLA. 



M.-\. Kl. 



Other inclusions consist of true eclogites. Among them some are well 

 preserved in their f»i-ii;inal habit wiiile others are greatly amphibolitized. 

 Fig. 1 6 (pi. Ill) shows an example in which all the pyroxene has altered 

 into a hornblende-plagioclase-mass with an ill-])reserved symplectic structure. 



TJic composition of Ihr Canui in the iMhrndoriir-roch. 



The analysis of garnet from labradorite-i'ock at Alvaerstremmen given 

 by Kolderup (see above p. 94) shows a mixture of nearly equal molecular 

 quantities of magnesia and ferrous oxide, besides a low quantity of lime. 

 The (|uantity of ferric oxide would seem to be exceptionally high, but the 

 disagreement of the figures from the garnet formula makes it probable that 

 this figure is too high. In other respects this garnet is exactly what we 

 call an eclogite-garnet. 



To learn more about the composition of these garnets I determined, 

 with prisms, the index of relVaction in three examples from the Bergen 

 region. The results are given below with the resulting probable composi- 

 tions. For comparison all. that is known about the garnet in the labradorite- 

 rocks from the Bergen and Sogn regions has also been quoted below. 



Probable 

 nj^^, Composition : 



1.7506 Fe.29Mg53Cai8 



1-7542 Fe3.2Mg5oCai8 



1-7541 Fe3,Mg.oCai8 



1-757 1 Fe34Mg4sCai8 

 Analyzed: 



— FeggMg^oCa.,, 



1.7658 Fe^sMg^^Cais 



1.7887 Fe.^MgggCa.,, 



Garnet from labradorite-rock, Mjeldem .... 



— „ — Arnevaagen . . 



Garnet from segregation, Saetre on Holseno 



Garnet from labradorite-rock, Okken, Sogn . 



— „ — Alvaerstrommen 

 Garnet from segregation, Aurlandsfjord, Sogn 

 Garnet from gabbro, Aardal, Sogn 



As appears, all the garnets from labradorite-rocks studied show a little 

 more magnesia than iron, while the garnet from gabbro in Aardal shows 

 iron predominating, being also in its occurrence more like common gabbro- 

 garnets, which were invariably found to be almanditic. 



The question now arises: is the presence of larger amounts of magnesia 

 in the garnet trom the labradorite-rocks than in the gabbro-garnets a con- 

 sequence of larger concentration ot magnesia in the rock, or is it due to 

 specific physical conditions ? 



As w-ill be shown latter, a somewhat high ratio of FeO is necessary for 

 garnet in the gabbroic rocks. The labradorite-rocks are an exception to 



