MICROSCOPICAL DESCRIPTION. Ill 



and the coarse feldspar meet each other for the most part in well defined 

 boundaries. In some places, however, a small amomit of finely granular 

 microcline occupies the space between them. Rounded grains of calcite, 

 pyrite and microcline are inclosed in the augite. The fracture lines affect- 

 ing the microcline sometimes extend uninterruptedly through an adjoin- 

 ing augite grain. 



Specimen 128 (130) has a more even and finer grained texture than the 

 preceding, and likewise a more uniform distribution of the constituents. 



In tliin section the microcline shows a less clearly defined grating 

 structure than in the foregoing, and occurs in irregularly angular and 

 rounded grains from two to five millimeters in diameter, usually sepa- 

 rated from each other by a network of finely granular microcline, inclos- 

 ing here and there larger grains of augite and a small amount of quartz, 

 titanite and calcite, but sometimes meeting each other along a common 

 boundary. The proportion of augite is much less than in most of these 

 rocks. The interstitial granular areas consist of very small grains of 

 microcline and augite, w^ith a small amount of clear, fresh-looking plagio- 

 clase feldspar between them in places. The augite does not appear to 

 have suffered much disarrangement of parts, though coarse fractures are 

 common. A small amount of pyroxene occurs in small grains distributed 

 in the granular microcline bands. In one instance a grain lying at the 

 intersection of three granular bands shows a line of fracturing extending 

 diagonally across the parallel cleavage, while narrow zones of hornblende 

 with faint pleochroisrn border a set of fractures developed transverse to 

 the cleavage. There is a slight difference in extinction and discordance 

 in the direction of the cleavage in the two parts into which the diagonal 

 crack divides the grain. Along this crack there appear small grains of 

 apparently fresh feldspar and one of titanite, together with several small 

 augite grains. A diallage-like appearance due to polysynthetic twinning 

 parallel to the orthopinacoid appears in some grains. No differences 

 were noted between the large idiomorphic augite grains and those appear- 

 ing in the granular areas. They show little evidence of alteration. More 

 or less quartz is present in the granular areas usually carrying rutile and 

 fluid inclusions and in some cases small rounded granules of augite. 

 Calcite, apatite, titanite and iron pyrites appear in small amounts. The 

 apatite carries small inclusions of quartz. 



Specimen 129 (131) resembles the last, except that the microcline has 

 a lighter color, giving the rock a fresher appearance. In general, the 

 texture is medium to coarse, with much larger grains of microcline scat- 

 tered through the mass. The augite and titanite appear quite uniformly 

 distributed, but on close inspection the former may be observed slightly 

 aggregated in anastomosing lines, giving an obscure net-like aspect. On 



XVI— Bui.L. Geoi,. Soc. Am., Vol. 7, 1895. 



