﻿50 NEW YORK STATE MUSEUM 



being in the amount of calcite, and that a very slow and gradual 

 change), seem more suggestive of regional than of contact meta- 

 morphism. On this view the belt would consist of original impure 

 limestones and calcareous shales, metamorphosed to the pyroxene- 

 feldspar-calcite combination, and with the tourmalin, actinolite and 

 epidote alone due to the later contact action. While unable to 

 definitely decide between the two, the first seems to us the more 

 probable. It is possible that the granite is close in place under- 

 neath the whole belt. In our view, then, the belt is due to the con- 

 tact action of an especial granite, its localization being thus ex- 

 plained, acting upon a limestone series of considerable thickness, 

 and certainly somewhat impure at least, as shown by the bands of 

 quartzite, amphibolite and mica gneiss within it. Part of the reg- 

 ular Grenville succession of the area consists of alternating thin 

 beds of limestone, various schists and an occasional quartzite, and 

 it would seem as if such a combination might well be turned over 

 into a group like that of the green schists by contact metamorphism. 

 This would be all the more likely if acted upon by two successive, 

 granite injections as is supposed to be the case here, since dikes of 

 Picton granite are believed to be present. 



The coarse pegmatite dikes of the north schist ridge, which furnish 

 well crystallized specimens of orthoclase and specular hematite, to 

 be found in many mineral collections, have already been described 

 by Smyth. 1 



Tourmalin contact zones in Alexandria. The Picton granite is 

 found cutting Grenville quartzite and amphibolite, but no other 

 members of the series, and the same is true of its known dikes ; that 

 dikes suspected to belong to it cut other members has just been 

 seen. This granite seems to have been much more potent in tour- 

 malin-forming capacity than any other granite of the region and 

 its contacts with the Grenville on Grindstone and Wellesley islands 

 are characterized by narrow tourmalinized zones which Smyth 

 has clearly described, as follows : 



Along their margins these dikes frequently show much black 

 tourmalin and this is usually most abundant in the very narrow 

 ones, in which the imperfect crystals of tourmalin interlock across 

 the entire width. At the same time the schists along the contact 

 become impregnated with fine, granular tourmalin, producing 

 strips and irregular areas of a lustrous black rock. The remarkable 

 feature about these contact zones in the schist is their extreme ir- 

 regularity in form and extent, and their entire independence of the 

 magnitude of the accompanying dike. A dike of granite a foot wide 



1 op cit. p. r94. 



