﻿Notes on Group of Thousand Islands. 269 



No. 16, which, on large weathered surfaces, exhibits an 

 indistinct gneissic or streaked structure, due to the 

 alternation of rude and ill-defined streaks or bands 

 composed of a very fine-grained mixture of quartz and 

 reddish orthoclase, with others holding a great number of 

 small, irregularly shaped or angular fragments of a 

 very dark-colored feldspar, apparently identical with that 

 seen in the Jupiter Island granite to be mentioned later, 

 and which are embedded in a similar line-grained ground 

 mass. Narrow strings of translucent quartz, evidently of 

 secondary origin, also occur occasionally running in the 

 same direction. The whole appearance conveys very 

 strongly the idea that the structure of the mass has 

 originated from movements in a softened mass of granite, 

 the finer granulated portions having been produced by 

 this movement and being most abundant where the 

 movements have been greatest. 



Of the granites above mentioned, that from Forsyth's 

 Island is rather coarse in grain and although uniform 

 in character and massive in general appearance, still 

 frequently shows, wdien examined closely, a rather distinct 

 parallel arrangement of the quartz in one direction. 

 It consists of red orthoclase, whose cleavage faces can 

 often be observed to be twisted, with bluish quartz, and a 

 comparatively small proportion of iron magnesia con- 

 stituents. Under the microscope a specimen of this 

 granite, taken from the quarry near Mr. Forsyth's house, 

 was found to possess the following characters : — 



Orthoclase and microcline are abundant, and are often 

 somewhat turbid from the presence of decomposition 

 products, while the lime soda feldspars are represented by 

 a few grains of plagioclase. The quartz, though less 

 abundant than the orthoclase, is present in large amount 

 and shows intense strain shadows. Every grain is twisted 

 or divided up into subordinate areas, ill-defined against 

 one another, but marking the tendency of the individual 



