156 THE VERMILION IRON-BEARING DISTRICT. 



waters, other changes of a far-reaching character have taken place in them. 

 In all of the instances which will be cited the chief agent of metamor- 

 phism appears to have been the contact action of certain intrusive acid 

 rocks. It is not for a moment to be supposed, however, that the 

 metamor2Dhism of the rocks should be ascribed solely to the action of these 

 intrusives; yet this is the most obvious cause, and probably the final 

 controlling cause. 



In the course of the field work on the Vermilion district, it was noticed, 

 when the exposures of greenstone possessing the general characters already 

 outlined for that rock were studied, that a great immber of them were cut 

 by dikes of acid rock, and that these dikes were of varying size. It was 

 further observed that near the central portion of the district these dikes 

 were relatively few, but that as the southern and northern limits were 

 approached they gradually increased in number until the greenstones were 

 in places literally permeated by dikes of acid rock. On continuing farther 

 from the central pai't of the district the main body of the granite was in 

 every case finally reached. When this body was reached, however, it was 

 found to contain occasional masses of Archean rocks of varying size, which 

 were practically surrounded by and thus included in the granite. The 

 relations are clearly those of intrusion, a younger acid rock being intruded 

 into and including fragments from the older Ely greenstone. In brief, 

 the relations are the same as those which exist between the batholiths of 

 granite and the contiguous greenstones of Rainy Lake" and Lake of the 

 Woods, and which have been so clearly described by Lawson. It was 

 further noted that this intrusion was accompanied by a marked change in 

 the character of the Archean complex. Where the granite dikes are few, 

 the characters of the greenstone formation remain essentially unchanged. 

 When the dikes have become numerous, however, the greenstones are 

 altered to amphibolitic anJ to a less extent to micaceous rocks, usually of 

 somewhat darker color than the normal greenstones. The main macro- 

 scopic characters are practically unchanged. Thus, for example, in these 

 amphibolitic rocks one can still recognize the characteristic ellipsoidal and 

 amygdaloidal structure of the greenstones. A splendid exposure of these 

 hornblendic rocks can be seen in the southeast quarter of sec. 3, and 

 the northeast quarter of sec. 10, T. 61 N., R. 14 W. These rocks, while 



« Report on the geology of the Rainy Lake region: Geol. Nat. Hist. Survey Canada, 1889, F. 



