﻿Yol. 64.] LA.TJRENTIAN SYSTEM IN EASTERN CANADA. 145 



Grenville Series rests, it has been proposed that the term 

 Laurentian be restricted to this great development of igneous 

 gneisses.^ 



The Grenville Series is thus separated from the Laurentian System, 

 and the name is employed to designate the sedimentary series which 

 overlies the lower gneisses and granites. The name Laurentian 

 will, in addition to its geological use, continue to have a geo- 

 graphical or physiographical significance, as, for instance, in the 

 term Laurentian Protaxis, which latter forms so striking a 

 feature of the continent of North America, and is underlain chiefly 

 by the gneisses of the Laurentian System. 



In its petrographical character and in the display of the pro- 

 ducts of metamorphism which it presents, this great area on the 

 southern border of the Canadian protaxis resembles in many respects 

 certain classic localities of the ' Grundgebirge ' on the Continent 

 of Europe,- but in none of them, with the possible exception of the 

 Scandinavian Peninsula, can the successive stages of the meta- 

 morphism be so clearly traced, or its final products be studied 

 in such enormous development. The area is very instructive, as 

 presenting a section of the deeper portions of the appareils 

 granitiques, the 'roots of the mountains,' laid bare for study 

 by the processes of denudation. 



The Laurentian protaxis from early times has been relatively an 

 area of progressive uplift ; while that of the great plains to the 

 south forms an area of progressive sinking, since upon it has been 

 deposited in successive stages a series of great systems of sedimentary 

 rocks. 



Here, along the border of these two great geological units, the 

 deep erosion reveals, it would seem, the mechanism of elevation, 

 the granite-magma rising from the depths, and in all probability 

 passing out from beneath the subsiding area to the south, lifting 

 the old Laurentian Highlands as the liquid in the Bramah press 

 lifts the ram when the piston sinks. 



X. Summary, 



(1) The Laurentian System of Sir William Logan in Eastern 



Canada consists of a very ancient series of sedimentary 

 strata — largely limestones — invaded by enormous volumes 

 of granite in the form of bathyliths, representing what 

 Logan termed the Eundamental Gneiss. 



(2) This sedimentary series is one of the most important deve- 



lopments of pre-Cambrian rocks in IS'orth America, and 



' 'Eeport of the Special International Committee on the Nomenclature of 

 the Pre-Oambrian Rocks of the Lake-Superior Region ' Journ, Geol. Chicago, 

 Tol. xiii (1906) p. 89 ; ' Report of a Special Committee on the Correlation 

 of the Pre-Cambrian Rocks of the Adii'ondack Mountains, the " Original 

 Laurentian Area " of Canada & Eastern Ontario ' ibid. vol. xv (1907) p. 191. 



2 A. Sauer, * Das alte Grundgebirge Deutschlands, &c.' Comptes Rendu*, 

 du IX^"^® Congres Geol, Internat. (Vienna) 1903, and other papers. 



l2 



