Lawson.] 



Malignite. 



353 



plane. It presents a distinct gneissic foliation in fractures transverse 

 to the plane in which the plates lie. The foliation is clearly original, 

 and there is no suggestion of cataclastic or even protoclastic 

 structure in thin sections of the rock. The orthoclase is remarkably 

 free from the molecular tension which is so characteristic of the 

 normal facies of the rock. The plates of orthoclase are commonly 

 slightly curved, and in some cases even distinctly bent, but the 

 phenomena of extinction due to this fact are quite different from 

 the optical tension shown by the poikilitic orthoclase of the normal 

 rock. 



The minerals of this facies of the rock have generally the same 

 characteristics as in the normal type. The aegerine-augite presents 

 the same pleochroism. The orthoclase is charged in the same 

 manner with dusty and rod-like interpositions, the latter usually 

 arranged in definite planes and presenting all the characteristics of 

 "Schillerization" products. The orthoclase differs, however, from 

 that of the normal type in being frequently twinned on the Carlsbad 

 law. It is practically quite fresh and sanidine-like, kaolinization 

 products being only occasionally observed in small areas. The 

 nepheline shows the same degree of alteration to cloudy products, 

 and the large apatites have the same irregular cracks and irregularity 

 in detail of their crystal boundaries as in the normal rock. 



THE GARNET- PVROXENE-MALIGNITE. 



General Features. — This malignite presents at least two fairly 

 distinct facies, which grade into one another in the same mass. 

 The dominant of these occupies the greater part of the south side 

 of the lake, being interrupted only by limited areas of rocks of the 

 nepheline-pyroxene-malignite type, whose special relations to the 

 garnet-pyroxene-malignite are not well defined, owing to the dense 

 vegetation. The minor facies is confined, so far as observation goes, 

 to the northwest corner of the west end of the lake near the 

 contact with the mica schists. The dominant facies presents a 

 remarkable appearance and appeals to the petrographer's eye as a 

 unique rock. The most prominent mineral is orthoclase, which 

 appears in the form of huge, thick plates of a light flesh tint 

 imbedded in parallel position in a dark green, moderately fine-grained 



