pratt] MODES OF OCCURRENCE. 27 
there so abundant, a norma] norite, containing nothing but a pla- 
gioclase feldspar and hypersthene, is extremely rare. There is more 
or less biotite, hornblende, or augite developed in nearly all rocks of 
this class, so that there is a gradual transition from normal norite to 
mica-diorite, hornblende-diorite, and gabbro. r rhe intermediate vari- 
eties are much more common than the extremes, and they have been 
classified by Williams according to the prevailing nonfeldspathic 
mineral. Where hypersthene prevails the rocks are grouped as 
noriles, being subdivided into normal norite, horneblende-norite, mica- 
norite, and augite-norite, according i<> the presence of these differenl 
minerals in the rock. These so grade into each other that no sharp 
line can be drawn between them. 
Associated with the norites, 3 and 1 miles southeast of Peekskill, 
N. Y. , are deposits of magnetite and emery. It is not at all unlikely 
that these veins are the products of the differentiation of the molten 
norite magma, by which the basic port ion of 1 he magma has been con- 
centrated near its outer surface, a gradual transition occurring toward 
the center to the more acid norite. This occurrence would be similar 
to that of the pyrrhotites which have separated out from the norites 
of Norway, as described by Vogt. 1 In that case the pyrrhotite was 
concentrated toward the border of the norite, and there is at some 
places a gradual transition from the pure pyrrhotite through a pyrrho- 
tite-norite to the pure norite, while at others there is a sharp contad 
between them. The deposit s of magnetite and emery are nol in a con- 
tinuous vein, but are more like segregated masses. Attempts have been 
made to work these for both iron ami emery, bill as iron-ore deposits 
they were soon abandoned. They are si ill being worked to a certain 
extent for emery by the Jackson .Mills Company, of Easton, Pa.; the 
Tanite Company, of Stroudsburg, Pa.: and II. M. Quinn, of Philadel- 
phia, Pa. An examination of the emery ore by .1. I). Dana 2 and G. H. 
Williams, 3 has shown that the corundum component is often scattered 
rather sparingly through the ore, and what had formerly been sup- 
posed to be green chlorite was found to be the iron-magnesian spinel, 
pleonaste. The corundum in the emery varies from small, colorless 
grains to crystals 7 mm. in diameter, which show a hexagonal outline. 
In other parts of the emery the corundum grains are larger and of a 
bluish color. 
The pleonaste, which is so commonly associated with the emery, 
has been found at the Cruger iron mine, in the eastern part of the 
township, as veins in a nearly normal norite, into which it passes by 
gradual transitions. The most compact specimens of the ore at this 
mine are found to contain the various mineral components of the 
norite, i. e., hypersthene feldspar, biotite, and garnet, no corundum 
having been observed here. 
1 Zeitschr. fair Prakt. Geol., Nos. 1.4, and 7,1893. 
2 Am. Jour. Sci., 3d series, Vol. XX. 1880, p. 199. 
3 Idem, Vol. XXXIII, 1887, i>. 194. 
