﻿Yol. 64.] LAURENTIAN SYSTEM IN EASTERIT CANADA. 141 



Oraigraount, a few miles beyond the north-eastern limit of the 

 Bancroft sheet. 



The nepheline-syenite and its associated alkali-syenites represent 

 a peripheral phase of the granite-intrusions. A description of 

 these rocks, with a discussion of their mode of occurrence and 

 genetic relations, will be found in the Transactions of the Royal 

 Society of Canada for the year 1908. 



VII. Contact-Phenomen^a about the Eoeders oe the 

 Granite-Bathyliths. 



About the borders of the various areas of granite and granite- 

 gneiss, contact-action is pronounced and often very striking. If 

 the invaded rock be amphibolite, fragments torn from it are found 

 scattered about in the gneiss, giving rise to inclusions presenting 

 the various characters already described. 



When the granite invades bodies of limestone, on the other 

 hand, the phenomena resulting from the intrusion are more varied. 

 The invading rock metamorphoses the limestone, and the products 

 of alteration may be divided into three classes : — 



(1) The alteration of the Hmestone into masses of granular green pyroxene- 



rock, usually containing scapolite, or into a rock consisting of a fine- 

 grained aggregate of scales of a dark-brown mica. 



(2) Intense alteration of the limestone along the immediate contact into a 



pyroxene-gneiss or amphibolite. 



(3) In addition to these alteration-products, in certain cases the granite 



dissolves or digests the invaded rock, after having altered it in one or 

 other of the manners above mentioned. 



The alteration-products of the first class may be considered as 

 due to the heated waters or vapours given off by the cooling magma, 

 that is, to be of pneumatolytic origin ; while the alteration-products 

 of the second class result from the more immediate action of the 

 molten magma itself. The products of these two classes of altera- 

 tion have much in common, however, and naturally pass one into 

 the other. 



The evidence of the alterations of the second class, whereby the 

 limestone is converted into amphibolite, is briefly as follows : — The 

 sedimentary series, consisting chiefly of limestones interstratified 

 with amphibolites, the former making up about one-half of the 

 volume of the whole, is invaded by the granite-bathyliths, torn to 

 pieces, and scattered as fragments through the invading rock. 

 These fragments are all composed of amphibolite, and none consisting 

 of limestone can be found. The persistence of this phenomenon 

 throughout the whole area suggests an alteration of limestone to 

 iimphibolite. 



In certain places, especially about the border of the Glamorgan 

 bathylith, where the line of contact is especially well-exposed for 

 study, a gradual passage of the limestone into amphibolite can 

 actually be observed, the former rock having gradually developed 

 in it felspars, hornblende, and pyroxene in progressively-greater 

 amount, until it eventually becomes an amphibolite (see fig. 3, p. 140). 



