& 
198 G. H. Williams—Norites of the “Cortlandt Series.” 
Section H. of Prof. Dana’s collection from 1 mile northeast of 
Colabaugh Pond, consists of magnetite and pleonaste mixed 
with about an equal quantity of colorless corundum. ‘This is 
in good sized grains ($-3™™ in diameter) with a high refractive 
index and often shows a sharp hexagonal section. These ex- 
hibit between crossed nicols, very brilliant interference colors. 
Frequently, iowever, they appear to be somewhat altered and 
then exhibit a gray tone with aggregate polarization. These 
corundum crystals contain inclusions in great quantity. These 
appear to be either magnetite in small rods or dots or reddish 
translucent plates of iron oxide. They are always massed to- 
gether in the center of the crystal, frequently in such abund- 
ance as to render this portion quite opaque. 
No. 126, from near Travers’ farm in the eastern part of 
Cortlandt township, is quite like the preceding, except that the 
corundum is much more abundant and present in individuals 
of much smaller size (44™™ in diameter.) The distribution of 
the inclusions is quite like that in the specimen last described. 
In some of the sections, the corundum is seen to have a deep 
blue color, and then to exhibit its characteristic dichroism. 
This is most notably the case in specimens taken from the 
Lombard mine, just north of Colabaugh Pond. This locality 
is represented by Nos. 136 and 137 of the University collection 
and by section A, belonging to Prof. Dana. These are seen un- 
der the microscope to be composed of an aggregation of the three 
minerals, fibrolite, corundum and magnetite. The first is pres- 
ent in long, colorless needles, showing the characteristic cleav- 
age, transverse parting, parallel extinction, and brilliant inter- 
ference colors of this species. They have their longest axes 
approximately parallel thus producing a somewhat schistose 
structure. The corundum is present in rather stout crystals, 
with a sharp hexagonal outline in cross-section. Such sections 
have in every position a uniform deep blue color, while those 
nearly parallel to the vertical axis have this color when their 
lateral axis is parallel to the principal section of the polarizer 
and a light greenish yellow tinge when brought into a position 
at right angles to this. The pleochroism is therefore: 
O=dark blue 
and the absorption O>EK. The hexagonal sections, when ex- 
amined in converged polarized light, show a uniaxial inter- 
ference figure and negative double refraction. All of these 
characters agree fully with corundum; and the examinations, 
for comparison, of sections of typical emery, from Samos, 
| E=light greenish yellow 
‘Naxos, Smyrna and Gumuch-dagh in Asia Minor and from 
Chester, Mass., leaves little doubt of the identity of these with 
the Cortlandt mineral. 
