68 NEW YORK STATE MUSEUM 



Other essential minerals. Apatite, ilmenite, pyrite and pyrrhotite 

 occur as accessories. This rock with decrease of augite becomes 

 the biotite-norite, and with occurrence of brown hornblende and 

 decrease of biotite and augite becomes the hornblende norite. Hyper- 

 sthene is the chief constituent of all the norites. It occurs in stout, 

 rounded prisms of different degrees of pleochroism. Oriented 

 ilmenite inclusions are common. The alteration is usually to ser- 

 pentine, but occasionally uralite forms. 



Olivine-pyroxenitc . This rock is made of augite or hypersthene 

 with varying amount of olivine. When the percentage of olivine is 

 large, the rock disintegrates easily into a coarse red sand. The 

 topography of this region shows numerous rounded hillocks. 



The proportions of pyroxenes vary; almost pure olivine-augite 

 and olivine-hypersthene rocks are known and basaltic hornblende 

 is a fairly constant component. The olivine makes up usually one- 

 fifth to one-third of the rock. It is colorless, but contains magnetite 

 inclusions. It is nearly always somewhat altered to serpentine. 



The contact rocks have been described in detail by Willi ;^ms.^'' 

 Staurolite, sillimanite, cyanite, and garnet, biotite and magnetite are 

 typical of the contact with the Manhattan schist. At the limestone 

 contact are pale green amphibole and pyroxene with rarer titanite, 

 zoisite and scapolite. 



Inclusions of schist, limestone and gneiss in the igneous rock are 

 common. The inclusions show more or less effect of absorption by 

 the igneous magma. 



The series as a whole shows little evidence of dynamic meta- 

 morphism except around the borders of inclusions, but there is a 

 banded gneissoid structure which is believed to be original and 

 proof of magmatic differentiation. " It appears that we have a 

 fairly complete and very intimate complex. ... In some 

 places the complexity of the mass is bewildering, while again we 

 may have several miles of a fairly uniform rock. . . . An 

 infinite number of species might be differentiated v/ithin this small 

 area of 25 miles" (p. 57). "The various differentiations of the 

 norite magma are most centrally located ; they are flanked on both 

 sides by pyroxenites and between the norites and the western area 

 of pyroxenites lies a diorite area. . . ." 



" The most basic members at least grade into one another in 

 many cases, while at times sharp contacts may be found. The 

 analyses of the more important types indicate an unmistakable 



"Amer. Jour. Sci. (3), 36:254. 1888. 



