On the Norian or "Upper Laurcntian" Formation, 419 



The mineralogical composition of the rock which con- 

 tains the precious labradorite has been the subject of 

 investigation ever since this mineral has been known. 

 Occasional hand specimens of the rock which have come 

 to Europe with shipments of labradorite have" been there 

 examined by many petrographers, and it has been found 

 to vary considerably. It has been called a gabbro, 1 a 

 norite, 2 an olivine-norite, 3 a labradorite rock, etc. ; and 

 whilst considered a volcanic rock by some, it has been 

 considered by others, on account of its irregular granula- 

 tion, to be rather referable to the crystalline schists. 4 



Wichmann also described, from the same region, a 

 diallage-magnetite rock, with olivine, plagioclase and 

 biotite as accessories. 



The anorthosite masses of this northern area have 

 evidently the same character as those described above 

 from the Morin and Saguenay districts, where hand speci- 

 mens of all the varieties may sometimes be collected in 

 one and the same locality. Wichmann has analysed the 

 labradorite rock, which consists of plagioclase and only a 

 little augite (see table of analyses, p. 436, No. XIX.) He 

 says that this is the prevailing rock about Nain. Bell, 5 on 

 the contrary, in his geological description of this part of 

 the coast of Labrador, does not mention any such rock as 

 occurring in the neighbourhood of Nain; he mentions that 

 the mountains in the immediate vicinity consist of a 

 " pale grey gneiss." Cohen also mentions quartz as an 

 ingredient of the hand specimens he examined. This 

 mineral was also found in small quantity in the anortho- 



i M. Cohen, Das Labradorit-fuhrende Gestein an der Kuste von Labrador. Neues 

 Jahrb. 1885, I., p, 183.— H. Vogelsang, Sur le Labradorite colore de la Cote du Labrador. 

 Arch. Neerland, T, III., 1368. 



2 J. Roth, Uber die Yerkommen von Labrador. Sitz. Berlin. Akad. 1883, p. 697. 



3 Van Werveke, Eigenthumliche Zwillingsbildungen, etc. Neues Jahib. 1883, II., 

 p. 97. 



4 A. Wichmann, Uber Gesteine von Labrador. Zeitschr. d. Deutsch. Geol. Gesellsclu 

 1884, p. 485. 



5 Bell, Keport of the Geol. Surv. of Canada, 1882-84, D. P., p. 11. 



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