Dresser — Geology of Bronte Mountain. 353 



The rock accordingly falls in 



Class II, Dosalane 



Order 5, Germanare 



Rang 4, Hessase 



Subrang 3, Hessose 



(Grad-polmitic) 

 (Sub-Grad. premirlic) 



Its actual mineral composition being practically normative, 

 and its structure megascopically granitic, the rock is, there- 

 fore, classed as a grano-hessose. 



2. Nordmarkose. — This is also a plntonic rock of medium 

 or coarse texture and gray or reddish gray color. In the hand 

 specimen it shows only feldspar with an occasional speck of 

 biotite. 



In the thin section feldspar is found to make up probably 90 

 per cent of the volume of the rock. The remaining constit- 

 uents in order of relative abundance are biotite, pyroxene, 

 hornblende, sphene, apatite. Biotite and pyroxene, and occa- 

 sionally hornblende, may be ranked as essential constituents. 

 Biotite more than equals in amount all the other constituents 

 except feldspar. Occasionally a little nepheline is seen and in 

 other parts a few grains of quartz. Logan mentions* the spe- 

 cific gravity of this rock as 2-632-2'638. 



The feldspar resembles orthoclase in its general appearance, 

 but has a mottled look, and under higher powers proves to 

 have a fine perthitic intergrowth in the spotted areas. 



These also are found to be more numerous under higher 

 magnifying powers, apparently their extent being limited only 

 by the power of the microscope. The feldspar is, therefore, 

 regarded as cryptoperthite. Logan (op. cit.) reported its spe- 

 cific gravity to be 2*575 and gave the following analysis (Y) of 

 selected grains. YI is an analysis of cryptoperthite from 

 Laurvik, Norway, by Gmelin, described by Brogger (Syenit- 

 pegmatitgange, p. 524). 



v. VI. 



Si0 2 .._: 65*70 65-90 



A1 2 3 20-80 19-46 



CaO ... -84 -28 



Na 2 _. 6-52 6'14 



K 2 6-43 6-55 



H 2 -50 -12 



Fe 2 3 __ -44 



100-79 98-90 



* Geology of Canada, 1868, p. 656. 



