180 THE CANADIAN NATURALIST. [May 



another granite containing much less hornblende than the second- 

 mentioned rock. These veins are, in their turn, intersected by a 

 vein of fine-grained granite, consisting of quartz and felspar, with 

 traces only of mica or hornblende. The specific gravities of these 

 different rocks were found to be as follows : — 



Hornblendic schist 2-836 



Syenitic granite 2-787 



Granite.." 2-608 



Fine-grained granite 2-630 



That the specific gravity of the last-mentioned rock should be 

 greater than the one preceding, is attributable to its containing 

 more quartz. Figure 1 gives a representation of the phenomcn i 

 here observed. No chemical analysis of these rocks is required to 



Fig. 1. 



a. Fragments of hornhlendic schist. 



b. Enclosing sj'entic granite. 



c. First intersecting granite. 



d. Second intersecting granite. 



show that the newer they are the greater are their contents in 

 silica. This is evident as well from their specific gravities as from 

 their mineralogical composition. The following relations, similar 

 to these are observable on the north side of the Montreal 

 River, at its mouth. The prevailing rock here is small-grained 

 granitic gneiss, which contains lighter and darker coloured portions, 

 according as the black mica which it contains is present in smaller 

 or larger quantity. A triclinic felspar is also noticeable in it. 

 Pieces of this rock are seen to be cut off and enveloped in a 



