138 G. H. Williams—WNorites of the “ Cortlandt Series.” 
his report on the geology of the first district of New York, as 
“syenite” and “hornblende rock.”* The next notice of the 
occurrence of hypersthene in the rocks near Peekskill was given 
by Prof. Jas. D. Dana, who identified and described it in con- 
nection with his studies of the rocks of Westchester County.t 
The comparative rarity of pure rock types in the Cortlandt 
Series above alluded to render various subdivisions under the 
hypersthene rocks necessary. I shall consider in succession: 
1. Norite proper. 
2. Hornblende Norite. 
3. Mica Norite. 
4. Hyperite or Augite Norite. 
5. Pyroxenite. 
1. Norite proper. 
As already stated, hypersthene rocks which are entirely 
devoid of mica, hornblende and augite are extremely rare 
within the Cortlandt region. Indeed it may be doubted if any 
specimen of the absolutely pure norite type could be found; 
and yet such are occasionally met with as contain these minerals 
in very small quantities. These specimens are regarded as 
representing the norite proper. 
Two thin-sections in Professor Dana’s collection, prepared 
from specimens collected at the iron mine three-fourths mile N.. 
15° W. of Cruger’'s station, show the norite type in greater purity 
than any others which have come under the writer’s notice. * 
They are almost wholly free from the non-essential minerals, 
only occasional plates of a very dark biotite being observable. 
The ground-mass is here a rather coarse-grained mosaic of 
plagioclase. The hypersthene is present in well-defined indi- 
viduals with a more or less rounded outline. This mineral is 
freer from inclusions and has a much lighter color than is usual 
in the Cortlandt norites. 
nachzuweisen sein, welcher das hiigelige aus steilen Beregkuppen bestehende 
Plateau bildet, das sich am linken Ufer des Hudson in 6stlicher Richtung von 
Peekskill, einer etwa 40 Miles von New York gelegenen Stadt, ausdehnt. Ich 
war verhindert diese Uebergange genau zu verfolgen, habe aber ein feinkérnig- 
syenitisches Gestein beobachtet, welches grosse Partieen von griiner Hornblende 
umfasste, in welcher kupfer-glanzende, scharf-begrenzte Hypersthen-Individuen 
lagen. Diese Gesteinsart scheint die Mitte der Uebergangstufen zwischen Hyper- 
sthenit und Syenit einzunehmen. .... Nordlich von Peekskill geht der Hyper- 
sthenfels wieder in Syenit tiber. Das zwischen beiden liegende Gestein, welches- 
Hornblende und Hypersthen zugleich enthalt, habe ich auch hier beobachtet.” 
—Zeitschrift der deutschen geologischen Gesellschaft.—Bd. xvii, 1865, p. 390. 
The gradual transition of the hypersthene rock into syenite and hornblende-schist 
does not in reality appear to exist. 
* Geology of New York—Part I, Geology of the First District by Wm. W. 
Mather, 1843, p. 528. 
+ On the geological relations of the limestone belts of Westchester County, New 
York. This Journal, III, xx, p. 197, Sept. 1880. 
