PEGMATITE, SILEXITE, AND APLITE OF NEW YORK 49 



than the syenite-granite series. Pegmatites seldom if ever occur 

 well within the larger areas of gabbro, and it seems that they formed 

 as satellites of the gabbro mostly in the marginal portions of the 

 stocks and to some extent at least in the closely adjacent rocks. 

 There are two features of special interest regarding these 

 pegmatites: first, that they are satelhtic developments of rather 



A^<OxQx| /ym •foliated gabbro '^^^^Foliated (gabbro 



Cidic peqma r- cc uui1h,quatU I IN -[-[-[-| A<r/(/^C pecjmaiitc MlhQu±quath 

 ^asic pegtriatite with, hornblende. 



Feet 



Fig. 7. — Sketch showing the relations of several facies of pegmatite to gabbro 

 at the northeastern edge of the stock on the hill one mile south-southeast of the Glen 

 in the North Creek quadrangle. 



basic gabbro, and, secondly, that the evidence strongly points to 

 the development of many of them while the parent magma still 

 possessed a considerable degree of fluidity. The following de- 

 scriptions and figures of selected examples will serve to make clear 

 the principal phenomena of the pegmatites in their relations to 

 the gabbros. 



One of the best places in the North Creek quadrangle to study 

 the relation of pegmatite to the typical gabbro is at the top of the 



