44 Til k Ottawa Naturalist. 



decomposed so that there is" little or no evidence of the lamellation of 

 the original felspar. The matrix in which these crystals are embedded 

 is an exceedingly decomposed grouudmass made up of felspar, epidote, 

 chlorite, hornblende and zoiaite, with larger individuals of augite in a 

 more or less advanced stage of uralitization. The alteration to horn- 

 blende is mainly marginal and has proceeded very unevenly, the core of 

 unaltered augite, having thus a very irregular outline. The augite has 

 a brownish colour and exhibits the characteristic interrupted cleavages in 

 cross-section. The larger individuals are all twinned, the twinning plane 

 being the orthopinacoid. The rock is so decomposed that the original 

 ophilic structure is nearly, if not quite, obliterated. Very little trace, if any, 

 remains of the original plagioclase of the ground mass, and instead 

 small areas or fragments of a water-clear unstriated felspar (albite?) are 

 present which are evidently secondary, as they contain minute embedded 

 needless of the secondary epidote. This water clear secondary felspar 

 has evidently been developed at the expense of the original plagioclase. ( i ) 



A considerable amount of ilmenite was originally present, but is 

 now almost altogether decomposed to leucoxene. This greyish white 

 translucent mineral occurs in masses which are generally irregular or 

 have a rude rhombic outline, and frequently exhibits the very charac- 

 teristic alteration along lines or zones parallel to the faces of the 

 rhombohedron. The thinnest section shows the mineral to be made up 

 of an aggregate of minute rounded grains with a high index of refraction 

 and showing brilliant interference colours. (2) 



9. Locality. \o miles north of Lake KLawachagami, on the portage 

 route between the Rupert and Eastnaain rivers, in the peninsula of 

 Labrador, Geo. Survey of Canada, Eastmain River. (3) 



Macroscopirally a dark greenish grey gabbro with yellowish green 

 phenocrysts of plagioclase. The phenocrysts have a tolerably sharp, 

 through irregular outline, the larger ones being over an inch in diameter. 



Under the microscope the rock is seen to be composed mainly of 

 plagioclase, augite and ilmenite. In places a coarse ophitic structure can 



1 1 1 'Rail, British Petrography, p. 230. 



(2) Notes on the microscopic structure of some i<>oks <>f the Quebec Group- 

 . I). Ada,n- Geo. Survey, Canada, Report Progress, 1880-82, p. 16, A. 

 Reference X<>. 1. p. 12. Book II, 12/7/92, Low. 



