phalen] the rocks of nugsuaks peninsula 20I 



brown surface, not characteristic at all. Evidently the olivine has 

 decomposed along its cleavage planes. In spots, the clear green and 

 rough surface of the mineral appear. 



The minerals, in their order of abundance, are olivine, feldspar, 

 pyroxene, iron ore, serpentine, calcite, and apatite. These are com- 

 bined in a hypautomorphic, holocrystalline mass with olivine, the 

 first mineral of the consolidation. This constituent is by far the 

 most abundant, occurring in irregular masses, with the usual 

 hexagonal forms. It is usually much shattered and fractured, due 

 to disintegration, which is far advanced in some of the crystals, and 

 which is accompanied by a copious deposit of iron ore in various 

 stages of hydration which has segregated along the cracks. 



In some of the olivines there is present what might be called at 

 first sight a pseudo-cleavage — very fine straight lines or spaces, for 

 the greater part normal to the pinacoidal cleavage, but often parallel 

 to this cleavage. With the highest powers of the instrument this is 

 seen to be due to lenticular masses of iron oxide, rather scattered 

 in the body of the crystals, but becoming more abundant near the 

 main cleavage cracks and finally disappearing in a pleochroic pig- 

 ment present in such cracks. Liquid inclusions are very abundant. 



After olivine had crystallized out, the next mineral to appear was 

 pyroxene. It occurs in irregular masses of light green color, with 

 prismatic cleavages well developed. Extinctions range as high as 

 44°, indicating an augite of intermediate alumina and iron content. 

 It is extremely abundant and shows no decomposition whatever. 



Magnetite, with other iron oxides, occurs in several forms in the 

 rock, inclosed in the ferro-magnesian constituents, rarely or never 

 in the feldspars. It is part original and part secondary, resulting 

 from the olivine. The original crystals are in the form of cubes 

 and octahedrons, sometimes twinned. Then there occur skeleton 

 crystals of the most wonderful patterns, as described by many 

 petrographers and figured by Pirsson^ and Hobbs.^ 



Magnetite occurs as an alteration product after olivine, often 

 clouding and rendering opaque whole phenocrysts of this mineral. 

 Patches of olivine are also rendered partially opaque by separated 

 red hydrous iron oxide. 



After these constituents, olivine, augite, and original magnetite, 

 had separated, the feldspar accommodated itself to the residual space. 

 It is remarkably fresh and, for the greater part, free from inclusions. 

 It occurs in lath-shaped forms twinned according to the Carlsbad 



^ Twentieth Ann. Rep. U. S. G. S., pt. in, 1898-99, plate lxxi. 

 " Twenty-Hrst Ann. Rep. U. S. G. S., 1900, pt. in, p. 65. 



