112 C. H. GORDON — SYENITE-GNEISS (lEOPARD ROCk) FROM CANADA. 



one side the specimen shows a flat surface, along which shearing has 

 taken place. 



In thin section in some areas a small amount of granular microcline 

 appears in the spaces between the larger grains. Plagioclase feldspar 

 occurs as small, irregular, unstriped grains in the interspaces and in 

 small amount as a cement. The microcline in general shows greater 

 alteration than in the ])receding specimen. Numerous particles of epi- 

 dote and occasional scales of biotite are scattered through it. Ei)idote 

 also occurs in connection witli the augite. 



The augite agrees with tliat of the preceding specimen. In one case a 

 grain having a pronounced twin lamination parallel to the vertical axis 

 has been much fractured and partially squeezed in two at the middle. 

 The two parts on either side of the major fracture are slightly changed 

 in orientation, while small grains of plagioclase, feldspar and green horn- 

 blende occupy the crack. A large grain of apatite inclosed in the augite 

 adjoins the crack. The augite is cut nearly parallel to the clinopinacoid, 

 00 P GO (010), and shows an extinction angle of 43° for the thicker lamellae 

 and 33° for the fine. It is evident, therefore, that the lamellar structure 

 is not due to a fine interlamination of an orthorhombic pyroxene (hyper- 

 sthene), as miglit Ije su[)i)osed, but re[)resents a multiple twinning, prob- 

 ably representing gliding planes, due to pressure. 



The part of the grain showing greatest fracturing also shows decompo- 

 sition products in greater abundance. These consist of epidote, calcite, 

 and hornblende; the latter in small i)leochr()ic grains scattered along the 

 fracture lines. In one case, showing (jnly i)arallel cleavage, the extinction 

 measured U[)on the cleavage lines was 13 degrees. In some cases an 

 a":<rre<'ate of small <rrains of auufite have a considerable amount of horn- 

 blende in the form of small (lakes and grains associated with the augite. 



J^rown ])iotite api)ears in small amount, a|)})arently as a decomposi- 

 tion product. 



A mass of rock four feet long, ol)served on the dump of opening num- 

 ber 11, showed the gradation from the first into the second or ellipsoidal 

 variety.* Specimen 136 (139, 140) was taken about 15 inches from the 

 ellipsoidal end of the block. It consists of coarsely crystallized areas of 

 feldspar and augite, with intervening areas in which the constituents 

 form a moderately fine grained mixture. The augite occurs in large 

 and small grains, the latter in the granular areas. The feldspar (micro- 

 cline) has a gray color and shows a sharp but variable reflection from 

 the cleavage faces. Twinned individuals having the greatest extent par- 

 allel to the twinning plane are common. The augite and titanite both 



♦ This block is represented in the collection by numbers 134, l.'jo, 136 and 137, taken in consecu- 

 tive order, the last number being the leopard rock. 



