﻿GEOLOGY OF THOUSAND ISLANDS REGION 5 1 



may have no contact zone, while a mere thread of granite a few 

 feet distant, may be bounded on each side by a band of the 

 tourmalin rock 2 or 3 inches wide. Again, the tourmalin, in- 

 stead of forming a continuous band, appears in lumps and bunches 

 of every conceivable shape, irregularly scattered along a dike, and 

 sometimes extending several inches away, at right angles to the 

 course of the dike. 1 



Tourmalin is also at times developed in the quartzite as well as 

 the schists, but not in the same definite manner, It is not at all 

 certain that dikes from the Alexandria bathylith are excluded from 

 the category of rocks producing this contact effect. In many cases 

 the dikes from the two bathyliths can by no possibility be distin- 

 guished from one another. In addition to these bands and bunches 

 of abundant tourmalin, developed in this localized fashion, more 

 scattered crystals of tourmalin, of the same evident origin, range 

 much more widely through the rocks. 



Smyth dissents from the view that the Picton granite was espe- 

 cially influential in the formation of these tourmalin zones, and in 

 other contact phenomena. He points out that, in his belief, the 

 tourmalin zones are most abundant at the extreme east end of 

 Wellesley island, quite remote from the Picton granite, though 

 with the Alexandria bathylith near at hand; also that the Alex- 

 andria bathylith is much nearer the Alexandria green schists than 

 the Picton. He therefore regards the Alexandria bathylith as 

 the most important granite of the region in producing contact ef- 

 fects. We are not sufficiently certain of the truth of the opposite 

 view to urge it, and simply chronicle the matter as one on which 

 we mildly disagree. It is not a matter of great importance in the 

 interpretation of the geology of the region, on the general features 

 of which we are in absolute agreement. 



Contact amphibolites. Adams has recently shown conclusively 

 that, in central Ontario, amphibolite occurs as a result of intense 

 contact alteration of Grenville limestone by granite, limestones pass- 

 ing into rocks in which pyroxene, hornblende, feldspars and scapo- 

 lite appear in increasing quantity up to final disappearance of cal- 

 cite, and with final entire replacement of pyroxene by hornblende 

 and scapolite by feldspar. 2 We have had the privilege of going over 

 his territory with him, and fully agree in his conclusions. Per- 

 haps the chief interest attaching to his work is the explanation 

 thereby afforded of the abundance of inclusions of amphibolite in 

 the Laurentian granite gneisses, where cutting the Grenville rocks, 



1 op cit. p. rgo. 



2 Adams, F. D. Jour. Geol. 177-18. 



