36 



Island of Montreal. It is a structure which 

 probably persists throughout the whole northern 

 protaxis of the continent [2]. 



(6) The invading granite not only exerted a mechanical 



action upon the invaded strata, but also by its 

 action upon these latter gave rise to a variety of 

 metamorphic products, among which one of the 

 most important is amphibolite produced by its 

 action upon the limestone. 



(7) The nepheline syenite is a peripheral phase of 



the granite intrusions, and is developed chiefly 

 along the contact of the granite with the 

 limestone. The nepheline syenite magma fre- 

 quently contained a large excess of alumina 

 which, upon the cooling of the rock, separated 

 out as corundum, giving rise to corundum 

 syenites, which are extensively worked for this 

 mineral. 



(8) The invading batholiths and allied intrusions of 

 granite appear to occupy the greater part of the 

 great northern protaxis of Canada, which has an 

 area of approximately 2,000,000 square miles 

 (5,000,000 sq. km.) It has therefore been con- 

 sidered advisable to restrict the name Laurentian 

 to this great development of the Fundamental 

 gneiss, which, although intrusive into the Gren- 

 ville series, nevertheless underlies and supports 

 it. 



(9) The relation of the Grenville series, forming the 



base of the geological column in Eastern Canada, 

 to the Huronian and Keewatin series, which are 

 the oldest stratified rocks in the western part of 

 the protaxis, has yet to be determined, the two 

 not having so far been found in contact; nowhere, 

 moreover, either east or west, has the original 

 basement upon which the first sediments were 

 laid down been discovered. These are every- 

 where torn to pieces by the granite intrusions of 

 the Laurentian. 



