22 Canadian Record of Science. 



Amphibolite, Township of Dysart, Lot #4, between Ranges 

 IX. and X. {Sections 1267 A.B.C.) 



This is a very dark fine-grained rock, foliated, but not 

 banded. 



When examined microscopically, it is seen to consist 

 very largely of hornblende, with a considerable amount 

 also of plagioclase. As accessory constituents there are a 

 little quartz, numerous individuals of biotite, a little 

 magnetite, sometimes enclosing pyrite, many small crystal- 

 line grains of apatite, and a very few small crystals of 

 zircon. 



The quartz grains are clear and glassy, and irregular in 

 outline. The plagioclase, which is generally fresh, is 

 sometimes twinned in broad and narrow bands, according 

 to the Albite law, occasionally also according to the 

 Pericline law. Cleavage is well seen in some cases, and 

 extinction is inclined. This is labradorite, having a specific 

 gravity of about 2.68 and an extinction angle, measured 

 On the twin-lamellae, of 18.° There is also a variety of 

 plagioclase which is perfectly clear, and is untwinned. It 

 has a specific gravity of about 2.65, and is probably 

 andesine. The biotite occurs in elongated pleochroic 

 individuals of brown color. It often includes grains of 

 plagioclase, and not infrequently penetrates individuals of 

 hornblende. This last-named constituent, which makes 

 up about three-fifths of the rock, is present in various 

 sized grains, often of irregular shape. It is dark brownish 

 green in color, pleochroism is intense, and the maximum 

 extinction angle is 30.° It seems to be micro-poikilitic 

 toward the feldspar, but this appearance is probably due 

 to its irregular form, caused by interference while 

 crystallizing. 



Sometimes interpenetration of the grains, sometimes a 

 mosaic effect is seen ; the structure is granulitic to granular. 



