MICROSCOPICAL DESCRIPTION. 



109 



greatest along the side adjacent to the granular area. As shown in figure 

 5, one fragment has been separated slightly from the main portion and 

 small grains of augite lie distributed along the crack. Some of the small 

 grains of augite are very slightly pleochroic, though the main part of the 

 crystal is not. 



In specimen 125 (127) the chief constituents are also coarsely crystal- 

 lized. The microcline has a purplish gray color, and incloses large prisms 

 of augite similar to that previously described, except as to the size of the 

 individuals. The pyroxene in the interstitial areas, however, is without 

 idiomorphic outlines, and occurs mostly in large, irregular grains and 

 aggregates. These are of a lighter green than the idiomorphic indi- 

 viduals in the microcline, and contain a larger number of inclusions of 

 feldspar, titanite and pyrite. This 

 becomes apparent in attempting 

 to select the augite for chemical 

 analysis. The anastomosing gran- 

 ular bands separate the rock into 

 angular lumps of irregular sizes. 

 These bands are not always plain- 

 ly apparent in the hand specimen, 

 but are revealed with distinctness 

 by the microscope. 



In thin section (number 127) 

 the coarsel}^ crystallized feldspar 

 shows a beautiful development of 

 the crosshatching of microcline. 

 The augite and large microcline 

 grains meet each- other with toler- 

 ably sharp boundaries, though a 

 small amount of granular micro- 

 cline and augite is sometimes observable along the line of contact. There 

 are also narrow bands of granular microcline extending outward from 

 the angle of the augite grain along the spaces between the large grains of 

 microcline. In these zones of granular microcline there occur also small 

 grains of plagioclase. Between the grains of microcline and plagioclase 

 there appears in j)laces, as a cement, a very small amount of feldspar in 

 which fine striations may sometimes be detected. 



The microcline is sometimes clouded and contains occasional small 

 plates of biotite, rutile needles, and apatite. 



The augite occurs in irregular grains, usually elongated parallel to the 

 vertical axis. It is of a pale green color and nonpleochroic. The pris- 

 matic cleavage is well developed. Cleavage parallel to the orthopinacoid 



Figure 6. — Section showing granular Band inter- 

 secting the Rock. 



v4/> = apatite ; {7 = quartz; P= plagioclase ; 7^/ = 

 microcline. 



