66 ■ 1'i:m II i.sKoi.A. M.-N. Kl. 



mass of protogine'. Tin- ni.iin rock of this (Tystalline nianth- is rcgardcfl 

 as paragneiss^. 



The massif ol' Aiguilles Konges is, according to the Swiss geo- 

 logists-^, composcfl fii' (lid highly iiictaiiiorphic sediments (Gneiss, . Glimmer- 

 schiefer), mainly in tin tnnii of hoiiifels, the petrosilex of de Saussure. 

 Kclogites are found near Lac (Ornu. In their vicinity there occur a 

 nLimber of lenses of sei-pentine"^. Ani|)liil)olilizatir)n of the eclogites is most 

 perfect at the contacts. 



Laura Llezner published a caieful investigation of the eclogites in 

 Otztal, TiroL^ and especially paid much attention to the alteration of 

 the eclogites into amphiholites. 'Lhis process, according to Hezner, always 

 works inwards, beginning from the margins, and therefore the masses of 

 eclogite are surrounded by zones of amphibolite. These masses are embedded 

 in a paragneiss which has not been studied more in detail. 



All these occurrences of eclogite — and still others could be mentioned 

 — are no doubt very similar to each other and to the Norwegian eclogites 

 in their mode of occurrence and general characters. Of these the Swiss 

 and I'irolian eclogites are said to occur as inclusions in sedimentogenous 

 gneiss^\ while all the other have been regarded as igneous gneisses. Other 

 eclogitic rocks are interbedded in series of micaschists, marbles and other 

 metamorphic rocks of para-character^. At present we may state, as a 

 summary on the occurrence of eclogites in gneiss, that a 

 1 a r £r e n u m b e r of them are inclusions in igneous gneiss. 



On the Genetic Connection between the Eclogites, Dunites 

 and Labradorite-rocks. 



As we have seen, some of the eclogites occur as inclusions in the 

 olivine-rocks, while others are inclusions in the gneiss and do not show 

 any direct connection with the olivine-rocks or the labradorite-rocks. Many 

 occurrences, however, afford a sufficient evidence that these three kinds of 



1 L. Duparc et I.. Mrazec, Recherches géologiques et petrographiques sur le massif du 

 Mont Blanc. Mém. Soc. Phys. et Hist. nat. 1898. 



2 Albert Heim, Geologie der Schweiz. Band II. Leipzig 1920, p. 219. 

 ■^ Op. cit. p. 232. 



't E. joukowsky. Sur les Eclogites des Aiguilles Rouges. These, Genève 1902. 



5 Laura Hezner, Ein Beitrag zur Kenntniss der Eklogite und Amphibolite, mit besonderer 

 Berücksichtigung der Vorkomnisse des mittleren Ötztales. T. M. P. M. 22, 1903. 



6 In the paragneisses of Mont Blanc and Aiguilles Rouges intrusive material is also 

 present (Joukowsky, op. cit.). It would seem probable to the writer that such might 

 possibly also be the case with the other alpine paragneisses h«re in question and in 

 such a case perhaps the mode of occurrence of the eclogite would not be materially 

 different from that of the inclusions in igneous gneisses. 



^ Cf. "The Mineral Facies," p. 184. 



