196 G. H. Williams—-Norites of the “Cortlandt Series.” 
magnetite, limonite, ilmenite, considerable light brown biotite 
and a colorless mineral which may once have been corundum, 
but which now shows only a very fine aggregate polarization. 
The Cortlandt ore, when examined under the microscope, 
exactly resembles the Bohemian hercynite. In the purest spec- 
imens, there is only the aggregate of bright green grains 
mixed with more or less magnetite. These grains are always 
of a much lighter color in contact with the magnetite. They 
contain no ilmenite plates, like the Bohemian mineral, but are 
full of irregular shreds and dots of magnetite. (Nos. 134, 148 
and 144 from the eastern part of the township.) Other speci- 
mens (No. 133 from Wm. Haight’s farm and I of Prof. Dana’s 
collection, from 1 mile northeast of Colabaugh Pond) contain 
more or less corundum scattered through them.* Sometimes 
this mineral is associated with fibrolite; and, in the section 
of Prof. Dana’s collection marked Cb4, from the Iron Mine 
south of the road south of Summer Hill, only fibrolite occurs 
with the pleonaste. This is interesting in connection with the 
intimate association discovered by Kalkowsky between the 
hereynite and fibrolite in the Saxon granulites.+ 
The spinel at the Cruger iron mines is quite like that in the 
eastern part of the township except that itis less pure. It 
occurs as veins in a typical norite into which it passes by grad- 
ual transitions. Hven the most compact specimens of the ore 
contain the norite minerals, hypersthene, feldspar, biotite, and 
garnet, mixed with it in greater or less quantity. At this 
loeality no corundum or sillimanite was observed. 
Quadrat remarked in 1845 that on account of its great hard- 
ness (75-8), the Ronsperg hercynite was employed, in the 
region near where it was found, as an abrasive agent. The 
admixture of true corundum, of course, very much increases its 
value for such purposes, and it is this which accounts for the 
opening of numerous emery mines in the eastern portion of 
Cortlandt township. 
According to the late Dr. J. Lawrence Smith, large deposits 
of corundum or true emery occur either associated with mag- 
netite on the contact between crystalline limestone and mica- 
schist (as in Asia Minor) or in connection with serpentine (as 
in North Carolina).§ Its association with spinel in massive 
rocks, where it is probably a product of contact metamorphism 
* The writer is under obligations to Professor A. H. Chester of Hamilton Col- 
lege for several interesting specimens of corundum altered to hercynite. They 
came from India and have been described by Genth, Proc. Am. Phil. Soc. Phila- 
‘delphia, Sept., 1873. 
+ Zeitschrift der deutschen geologischen Gesellschaft, 1881, p. 537. 
Ib C105 BOUe 
cee on Emery, this Journal, 1850, p.354. Annales des Mines, 1850, p. 
259. Original Researches, 1884, p. 75. 
