86 ANNALS NEW YORK ACADEMY OF SCIENCES 



sometimes these varieties are found banded together in flow-like masses. 

 The diorites must have come next, since the granites were evidently the 

 last to form. 



Dikes are abundant throughout the series and vary in composition 

 from pegmatite to peridotite. 



Many inclusions of schist, and some of limestone and gneiss, are found 

 in the district. These are most prominent in the large diorite area and 

 in the district near Salt Hill. At times, they have been absorbed by the 

 molten magma, giving rise to very abnormal rocks. Contact metamor- 

 phism is also apparent around them, and on the borders of the series in 

 places, developing in the schist an abundance of biotite, quartz, mag- 

 netite and many aluminous minerals; and in the limestone wernerite, 

 diopside and other lime compounds. 



Dynamic metamorphism is indicated by all of these rocks to a slight 

 though constant degree ; but this metamorphism sometimes .assumes very 

 marked proportions around the foreign inclusions in the district and in 

 places from which the emery has been mined. 



The economic geology is confined chiefly to granite quarrying and 

 emery mining. The emery has been generally considered as an example 

 of magmatic segregation, but more detailed work would seem to indicate 

 that it is due to the absorption of sedimentary xenoliths. This would 

 give rise to a magma supersaturated with respect to iron and alumina, 

 from which emery would separate out according to the laws formulated 

 by Morozewicz. This view of the origin of the emery is supported by 

 its frequent, somewhat remote association with visible inclusions of 

 schist ; by its association with exactly the same suite of minerals as those 

 developed on the borders of the district and in certain inclusions whose 

 relations are unmistakable, and by its frequent occurrence banded with 

 quartz, sometimes contorted and resembling exactly a black quartz schist. 



