ORIGINAL BANDED STRUCTURE 263 



"mosaic" types of- injection as described by Gushing; (2) by simple 

 melting and absorption of borders of small and large inclusions, and (3) 

 by engulfment and partial to complete assimilation of Grenville frag- 

 ments or inclusions. 



Original banded Structures in the Syenite and Granite 



Features of special interest in connection with the granites and sye- 

 nites, especially the former, are the frequent and comparatively sudden 

 transitions from the gray to the pink varieties and from the more sye- 

 niticor basic phases to the more truly granitic phases. The effect is to 

 give wide bands or layers, from 1 or 2 to 100 or more feet wide, of vary- 

 ing color and composition, and. 3^et all clearly belonging to the same rock 

 mass because of the true, though often pretty rapid, gradation of one 

 band or layer into another. These bands always appear to be arranged 

 parallel to the foliation. Many examples of such phenomena have been 

 observed by the writer. 



Gushing and Kemp have described such banded rocks in the Long 

 Lake"^* and Elizabethtown-Port Henry^^ quadrangles, respectively, and 

 they are inclined to regard the banding as due to differentiation of the 

 magma into layers of varying composition. For many cases, at least, the 

 writer agrees with this view, though in certain other cases, however, he 

 believes the banded structures have been produced by more or less thor- 

 ough fusion, but only partial assimilation of long, narrow Grenville 

 gneiss inclusions. Detailed records of observations in support of this 

 view are being accumulated, and the results will be presented in a later 

 paper. 



3* H. p. Gushing : N. Y. State Mus. Bull. 115, 1907, p. 478. 



35 J. P. Kemp : N. Y. State Mus. Bull. 138, 1910, pp. 48 and 128. 



