﻿146 PEOF. F. DAWSON ADAMS OM THE [May I908, 



presents the greatest body of i)re-Cambrian Jimestones on 

 that continent. 



(3) This great pre-Cambrian limestone series is best designated 



as the Grrenville Series. 



(4) The invading bathyliths of granite are of enormous extent. 



They possess a more or less distinct gneissic structure, due 

 to the movement of the magma which developed a fluidal, 

 and, in the later stages of intrusion, a protoclastic structure 

 in the rock. 



(5) The granite-gneiss of the bathyliths not only arched up the 



invaded strata into a series of domes, but ' stoped ' out 

 portions of the sides and lower surface of the arches, the 

 fragments torn off from the walls and roof by the in- 

 vading granite being found scattered throughout the mass 

 of the invading rock. This ' stoping,' ^ however, probablj^ 

 developed only a small part of the space which the granite 

 now occupies. 



This structure is thus identical with that found by 

 Prof. Lawson in the Keewatin area of the Lake-of-the- 

 Woods district, west of Lake Superior, and by the present 

 writer in the district north of the Island of Montreal. 

 It is a structure which probably persists throughout the 

 whole northern protaxis of the continent.^ 

 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 frequently 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 bathyliths 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. It has therefore been considered advisable 

 to restrict the name Laurentian to this great develop- 

 ment of the Eundamental Gneiss, which, although 

 intrusive into the GrenviUe 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 



^ See E. A. Daly, ' The Mechanics of Igneous Intrusion ' Amer. Journ. Sci. 

 ser. 4, vol. xv (1903) p. 269. 



^ F. D. Adams, ' On the Geology of a Portion of the Laurentian Area lying 

 to the North of the Island of Montreal ' Ann. Eep. G-eol. Surr. Can. n. s. 

 vol. viii (1896-97) part J. 



