MICROSCOPICAL DESCRIPTION. 



115 



The plagioclase is generally fresh, with sharply defined striations, but 

 in some cases is without stripes and more or less cloudy. It contains 

 an abundance of nodular quartz inclusions. The constituents of the 

 granular areas show a tendency toward the micropoikilitic structure. 



The augite occurs in grains and aggregates distributed in a belt along 

 the middle of the granular band. The grains are irregular in outline and 

 often elongated parallel to the vertical axis. The grains usually lie with 

 their long axis approximately parallel with the direction of the band, but 

 in many cases they lie transverse to it. The augite grain is often pleo- 

 chroic, but without distinct evidences of alteration. It does not differ 

 essentially from that of the coarse grained rock. Pinacoidal and prismatic 

 cleavages are usually well developed in the larger grains. 



Apatite occurs sometimes in 

 large elongated grains lying par- 

 allel with the general lamination. 

 They carry numerous quartz in- 

 clusions, sometimes in short 

 prisms terminated at each end by 

 the pyramid. 



A small amount of calcite is 

 present. 



In specimen number 142 (147, 

 148, 149) the feldspathic lumps 

 are mostly small, usually much 

 elongated, and very irregular in 

 shape. The pyroxene is abun- 

 dant in the interstitial areas, but 

 is not regularly distributed. In 

 places it occurs in lumps of con- 

 siderable size, in which there ap- 

 pear grains of quartz and feldspar and a considerable amount of titan- 

 ite. The flattened feldspathic lumps arrange themselves somewhat 

 concentrically about these aggregates. The flattened feldspathic masses 

 are relatively small near the central augite aggregate, but increase 

 rapidly in size outward. Often the augite lump represents simply a 

 local thickening of the interstitial band. The augite is of a dark green 

 color and occurs in comparatively large prisms, those of the segregated 

 masses occasionally exhibiting crystallographic outlines. In the inter- 

 stitial bands the prisms sometimes arrange themselves transversely and 

 project more or less into the feldspathic masses on either side. The 

 feldspathic lumps are made up of a groundmass of fine grained .feldspar 

 and quartz inclosing large, often twinned, tabular grains of microcline. 



Figure 7. — Section transverse to the Pyroxene Band 

 in the ellipsoidal Syenite-gneiss. 



Showing prisms of augite lying in the granular 

 bands and transverse to it. 



