86 



NEW YORK STATE MUSEUM 



AMPHIBOLITE INCLUSIONS 

 The age and nature of the hornblendite xenoHths, however, offer 

 a special problem of no little difficulty in the interpretation of local 

 Precambrian geology, and it would be merely begging the question 

 to use their presence in the granite as an argument for the greater 

 age of the gabbro-diorite. On the other hand, once it is shown by 

 independent considerations, as by the above study of the pegmatites, 

 that the available evidence favors the greater age of the gabbro, 

 then the great abundance of amphibolite inclusions lends additional 

 weight to the view. Until Professor Smyth in 1895 showed the 

 greater likelihood of their being older than the granite, the general 

 tendency had been to regard such inclusions as dikes, broken and 

 bent by subsequent crustal displacements. For a full discussion of 

 this point, reference should be made to Smyth's paper, where their 







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Fig. 18 Broken amphibolite inclusion in granite gneiss, showing parts 

 entirely separated b}- movement in viscous magma, the spaces being filled 

 with pegmatite. Fragments average about 18 inches in thickness and 

 strike northeast, (a) Pink granite gneiss grading into pegmatite; (b) frag- 

 ments of an amphibolite inclusion. 



One and five-tenths miles east by north from Eddy, near schoolhouse. 



xenolithic character is discussed at length (Smyth 1898, pages 490- 

 92). It may be briefly pointed out, however, hovv' the evidence at 

 two or three points on the Canton sheet clearly substantiates the 

 general conclusions arrived at in the paper cited. 



For example, at the offset intersection of the northeast and 

 northwest roads 1.5 miles east of Eddy there is a flat, glaciated 

 ledge of granite gneiss containing a string of amphibolite inclusions 

 which have been stretched out over a total length of 75 feet or more 

 (see figure 18). Manifestly these are parts of a once continuous 

 sheetlike mass of hornblende schist which was broken to pieces by 

 movements in the somewhat viscous granite magma. The spaces 

 between the fragments are occupied by pegmatitic and coarsely 

 granitoid material, which, being less viscous than the parent magma 



