Petrographical Relations of Laurentian Limestones. 23 



Quartz Diorite Gneiss, Township of Glamorgan, Range IJl-> 

 Lot 8. (Section 1&74)- 



This is a dark gray rock, fine-grained, foliated and banded, 

 composite bands alternating with light colored and dark 

 colored bands. Microscopically the foliation is shown 

 extremely well by the parallel arrangement of the minerals. 



The rock is found to be composed essentially of quartz, 

 plagioclase, and hornblende, while in certain bands biotite 

 is common, and in others microcline occurs. A very few 

 individuals of orthoclase, a little sphene, with titanic iron 

 ore, and a few small crystals of apatite are the accessory 

 constituents. 



The quartz occurs in large and small irregular grains, 

 often cracked, or showing undulose extinction. Th e 

 orthoclase is quite fresh, except along the cleavage planes 

 where it is apt to be turbid. It sometimes shows parallel 

 extinction, and is usually untwinned. The microcline is 

 in irregular individuals of medium size. The plagioclase 

 is oligoclase. It is sometimes turbid, and frequently 

 cracked. It is well twinned in broad, narrow, and alter- 

 nately broad and narrow bands, sometimes also according 

 to the Pericline law. The biotite is in very elongated 

 individuals, with cleavage distinct, and pleochroism very 

 marked. In some cases it gives evidence of strain by the 

 bending and crumpling of the plates. Lath-shaped indi- 

 viduals of this mineral frequently penetrate grains of 

 hornblende. The hornblende occurs in large and small 

 individuals of very irregular form. It is deep brownish 

 green, with strong pleochroism, and an extinction angle 

 of 28.° The sphene is in small irregular masses, much 

 cracked ; pleochroic from nearly colorless to light brown- 

 It often surrounds as a more or less even border, particles 

 of black titaniferous iron ore, which is also found withou 

 the sphene. 



The structure is granular, approaching granitic, the 



