﻿148 THE LATJRENTIAN SYSTEM IN EASTEEN CANADA. [May I908, 



fresh contribution to our knowledge of the oldest rocks of a region 

 which the labours of Logan and his associates had made classic 

 ground in the history of Geology. 



Dr. Teall said that, in the absence of the Author, and with only 

 a portion of the paper before them, anything of the nature of 

 criticism would be out of place. It was evidently a most important 

 communication. The results of the detailed mapping of a portion 

 of the typical Laurentian area appeared to show that the relations 

 of the granitoid gneisses to the surrounding rocks were similar to 

 those of the more or less allied rocks of the Rainy-Lake region 

 described by Prof. Lawson many years ago. 



With regard to the formation of amphibolites in different ways, 

 he could only say that he had not met with any evidence in support 

 of the view that amphibolites having the same structure and 

 composition could be formed from the alteration of both impure 

 limestone and basic igneous rocks. 



Mr. Baeeow regarded the paper as of great importance, throwing 

 a very suggestive light on problems that were met with in the 

 Scottish Highlands. The oldest rocks of that region are sedi- 

 ments, together forming a huge aureole of therm ometamorphism, 

 and while they show their least altered aspect along the southern 

 Highland border, they become increasingly metamorphosed towards 

 the north-west, the alteration extending from near Stonehaven to 

 Omagh in Ireland. In the centre of the aureole, where most highly 

 crystalline, they are flooded with granitic material which has assumed 

 a foliated structure. This gneiss, as in the Laurentian area, tends 

 to occur in a laccolitic form, usually built up of a vast number of 

 slightly-separated sills. 



The speaker had been led to the conclusion that the Lewisian 

 gneiss is essentially a sill-like or interlacing mass nearly horizontal, 

 intruded into the Highland rocks, and that it occupies approximately 

 a definite stratigraphical horizon defined by certain limestones and 

 shales, just as the Laurentian gneiss was held by the Author to be 

 an intrusive mass at the horizon of the Grenville Limestone. 



