phalen] the rocks of nugsuaks peninsula 205 



splendid basal parting in many of its lath-shaped forms, and the 

 process of alteration has begun along these planes of weakness, but 

 not always, for peripheral alteration has advanced to such a degree 

 that it must have been at least simultaneous with, if not antecedent 

 to, the changes along the basal partings. This alteration has filled 

 the space originally occupied by the feldspar with a greenish sub- 

 stance, which, for want of a better term, I have referred to as viridite. 

 In part this viridite is very dark bottle green, changing through 

 various greenish and yellow shades to a bright saffron yellow. Un- 

 doubtedly much of the pigment of the viridite is iron oxide in various 

 stages of hydration. In plain polarized light and with the very high- 

 est powers these pigments seem to be made up of shapeless patches 

 of brownish-yellow material with occasional specks of magnetite and 

 lath-shaped particles, all identical with that observed in the basal 

 partings of the plagioclase. 



Needles of apatite are abundantly scattered throughout, while 

 underlying the heterogeneous mass may be observed the faint 

 grayish-blue interference tints of the feldspar. Hence it is plain that 

 these decomposition products owe their origin to the feldspar 

 chiefly and not to the augite. We also have in these abundant 

 products a ready explanation of the brilliant reddish hue of the 

 plagioclase observed in the hand specimen. 



In spite of its almost completely altered condition in places, the 

 feldspar at times is even fresher than the augitic constituent. This 

 is the exception, however, and not the rule. It is fortunate, how- 

 ever, in that it enables the feldspathic minerals to be diagnosed with 

 no difficulty whatever. Its extinctions range in the neighborhood 

 of 25°, the maximum symmetrical extinctions obtained being 26.3°. 

 The feldspar, then, is a typical labradorite of composition AbiAn^. 



Of the accessory constituents, olivine was noted in a few sections 

 in an advanced state of change. It appeared with its usual comple- 

 ment of cracks, filled with dark-brown ferruginous matter. Cavities 

 are rather numerous ; in many instances their outlines are suggestive 

 of the former presence of olivine. Even were olivine present to this 

 extent, it would still be classed as a minor accessory. 



Iron ore is present in considerable quantity. It is confined to the 

 decomposed portions of the rock almost exclusively and is very 

 irregular in outline. Although present in large masses, it appears 

 to be at least in part secondary. Much of this dark opaque mineral 

 is pleonaste. Chlorite is present in small quantity, bordering the 

 augite. Calcite, in tiny anhedrons, also occurs as a decomposition 

 product. Apatite has already been referred to. 



