﻿Yol. 64.] LAURENTIAUr SYSTEM IN EASTERN CANADA. 133 



proportion far exceeding in amount that o£ the potash-felspar, 

 a fact which is also shown by separations with Thoulet's solution. 

 The rock takes its place in the Quantitative Classitication as a 

 lassenose. 



No. II is seen under the microscope to be composed essentially of 

 felspar and quartz, with a small amount of biotite. Uritwinned 

 felspars, apparently orthoclase and microcline, are present in large 

 amount, and the proportion of felspar-grains showing the ordinary 

 albite-twinning is small. A little iron-ore and a very few minute 

 individuals of apatite and zircon complete the list of constituents 

 present. A separation of the constituents of the rock by means of 

 Thoulet's solution showed that the amount of oligoclase present was 

 considerably greater than that of orthoclase and microcline taken 

 together, a conclusion confirmed by the analysis. This, when 

 calculated out, shows the rock to have the following percentage 

 composition (mode) : — 



Orthoclase 25-58 



Albite 29-34 



Anorthite 5-00 



Quartz 37-68 



Biotite 0-90 



Magnetite 1-39 



Water 0*26 



Total 100-15 



It will thus be seen that the amount of anorthite present is 

 sufficient, when united with the albite, to give 34*34 per cent, of an 

 acid oligoclase having the formula AbgAn, thus bearing out the 

 results obtained by the Thoulet separation. This combination, as 

 compared with the orthoclase, is present in about the proportion of 

 3 to 2. This rock, in the Quantitative Classification, isatehamose. 



Throughout the granite-gneiss almost everywhere in the area dark 

 inclusions are present. These are often very abundant, and consist 

 of amphibolite or closely- allied rocks. Their presence in the Bancroft 

 area has in the accompanying map (PI. XIII) been emphasized 

 at the expense of artistic effect by printing dark-green spots upon 

 the granite wherever these amphibolite-inclusions are abundant. In 

 some places, on account of their abundance and angular character, 

 the granite presents the appearance of a breccia. These fragments, 

 while usually more or less angular, have sometimes been softened 

 and drawn out in the direction of the movement of the gneiss so as to 

 impart to the rock a streaked or banded appearance (see fig. 2, p. 134). 

 In other places, the inclusions have been so completely permeated 

 by the granite-magma that they are utterly disintegrated. Every 

 stage of passage from the sharply-angular inclusions to the final 

 products of disintegration can be traced in many places, although 

 in most cases the inclusions are well marked and sharply defined 

 against the enclosing gneiss. At many points throughout the red 



