110 C. H. GORDON — SYENITE-GNEISS (lEOPARD ROCK) FROM CANADA. 



and clinopinacoid is common, though usually less distinct than the pris- 

 matic. Grains in which the cleavage parallel to co P co (100) is well 

 develo[)e(l, giving a diallage-like appearance, are frequent. This is often 

 made more apparent by the presence of thin twinned lamelUe i)arallel to 

 the same plane. Inclusions of feldspar, sometimes showing the cross- 

 hatching of microcline, occur in the augite. Grains of pyrite occur along 

 the cleavage, as also small, irregular flakes of hornblende. The liorn- 

 blende is green and pleochroic in green and greenish yellow colors. . 



The alteration of the augite to compact hornblende was clearly demon- 

 strated by the presence of the latter along the fracture cracks of the former. 

 At one point in the crack there is a small grain of compact green horn- 

 blende partially inclosing a grain of iron ore. The hornblende shows 

 well marked parallel cleavage and distinct pleochroism. In addition to 

 this, the irregular fracture lines of the augite are bordered on either side 

 by a thin greenish band, differing from the augite in its double refrac- 

 tion and showing distinct pleochroism. These bands are in direct con- 

 tinuity with hornblende in the larger space and must be regarded, there- 

 fore, as the same. The zone of hornblendic su'bstance is often observed 

 along the fracture lines in the augite and grading into the latter. They 

 are so narrow, however, that, though showing a slight degree of pleoch- 

 roism, tlieir identity is clearly established only when found in direct con- 

 nection with larger recognizable masses. 



The apatite occurs both in the form of microscopic inclusions in tlie 

 microline and as rather large rounded grains, l)oth in the microline and 

 in the interstitial areas. These often inclose small grains and i)risms with 

 pyramidal terminations, liaving a lower index of refraction, which are 

 ])robably (quartz. In one of these inclusions the extinction was found to 

 be parallel to the longer axis. 



In thin sections of si)ecimen number TiG (1*28), which resend)les the 

 preceding, the granular zones are narrow and consist chiefly of microcline 

 with a very small amount of plagioclase. The large grains of microcline 

 show the characteristic microperthitic intergrowth with albite (?). 



The microcline holds as inclusions numerous small biotite plates, apa- 

 tite, rutile needles, and an abundance of fluid inclusions. The biotite 

 plates are often distributed along the cleavage in ])arallel lines or bands. 

 In other cases they appear in consideral^le numbers in ]3risms and hex- 

 agonal sections in intersecting parallel lines corresponding to the cleavage. 

 Dust-like decomposition products appear quite aljundant in some areas, 

 and especially along fracture lines. 



An aggregate of augite grains, with irregular, but rounded, outline, oc- 

 cupies the space between two large microcline individuals. 'J'he augite 



