r92 



NEW YORK STATE MUSEUM 



Uut as regards the relative age of the granite and the granite- 

 gneiss there is less certainty. As a whole, the granite is more 

 massive, and thus a younger looking rock than the gneiss, but 

 when the former becomes well foliated, as it often does, it is prac- 

 tically identical with the gneiss. The most constant petro- 

 graphic distinction in the field is the presence of the opaque white 

 or blue quartz in the granite, but even this fails in the gneissic 

 phases. Coleman 1 , in describing the same granite in the Cana- 

 dian islands, mentions it as cutting and including the gneiss, and 

 his data are conclusive, but it is not certain that he uses the 

 term, gneiss, in the sense in which it is here employed. Certainly, 

 the writer could find no instances of the granite cutting the gran- 

 ite gneiss, or of inclusions of the latter in the former, though in- 

 clusions of the quartzite and schist are abundant. 



As above stated, the term, gneiss, is here used to embrace a 

 complex of granitic gneisses, known to vary in age, though all are 

 younger than the schist, but so closely related and so inter- 

 mingled that their separation is often impossible. It would be 

 ent irely consistent to map the Grindstone island granite as a pari 

 of the granite-gneisis, regarding it as probably the youngest mem- 

 ber of this complex formation in this vicinity. But, on account 

 of the prevailing massive habit of the granite, which, with its 

 location, tends to differentiate it, also on account of its previous 

 classification, it is here mapped separately. That it lias a close 

 genetic relation to the granite-gneiss as a whole, and is identical 

 with part of the latter as here mapped, is certain. Indeed, the 

 distinction between the two rocks on Wells island is conjectural. 

 In these respects, tin 4 granite occupies a position similar to that 

 of t he granites in Gouverneur and the syenite in Diana, described 

 in previous reports. 



Passing to the south bank of the river, the granite-gneiss mixed 

 with schist stretches from Chippewa to Collins Landing, a dis- 

 tance of about 20 miles. 



A beautiful instance of schist inclusions in the granite-gneiss 

 is shown at Alexandria Bay, in a lot at the corner of the Tied- 



'Canadian record of science. 



1:127. 



