G. H. Williams—Norites of the “ Cortlandt Series.” 189 
Shde No. 118 of the Johns Hopkins University collection, is 
of a rock from the same locality asthe twojust mentioned. Itis 
essentially the same as the preceding but contains as additional 
constituents pleonaste and garnet. The relation of the first of 
these minerals to the norite is very interesting and will be more 
fully described beyond. The garnet here forms narrow borders 
around the iron minerals. Here again the hypersthene and 
feldspar are unusually light colored and free from inclusions, 
a fact which may indicate tliat nearly all the iron present in 
the magma crystallized in the ores. 
No. 48, from Shaw’s blacksmith shop near the railroad cross- 
ing at Centerville on the road to Peekskill, exhibits a very 
interesting variety of the typical norite containing large por- 
phyritic crystals of orthoclase. At first glance this rock in 
the hand-specimen appears like a medium grained aggregate of 
reddish brown feldspar and glistening bronzy hypersthene, but 
a closer examination reveals the presence of long, narrow cleavage 
surfaces of feldspar. Some of these measure as much as 10 
60™™"! The crystals are elongated in the direction of the clino- 
diagonal axis,as may be seen from the direction of the cleavages. 
The highly reflecting surfaces are everywhere sprinkled with 
dull spots which the microscope shows to be inclusions of the 
other constituents in grains of the usual size. Here, therefore, 
we have avother example of the structure which the writer has 
distinguished as peciltic* in describing the hornblende of the 
Cortiandt peridotites. 
A careful examination of this feldspar leaves little doubt as to 
its being a true orthoclase. Its specific gravity, determined by 
the Thoulet solution and a Mohr’s balance, is 2°615. The pow- 
der, which was completely isolated from the other constituents, 
gave a strong potassium reaction. A series of measurements 
on the reflecting goniometer gave, for the angle between the 
two cleavage planes, values varying from 89° 35’ to 90° 44’, a 
slight uncertainty being occasioned by the somewhat undulatory 
character of the cleavage surfaces. Stauroscopic determinations 
of the extinction angles, made on carefully detached cleavage 
pieces, yielded values averaging 54° for wP m (010) and 0° for 
OP (O01). 
This feldspar also differs in several other particulars from 
the small reddish brown plagioclase crystals which, as usual, 
make up the greater part of the Cortlandt norite. Twinning 
lamelle are altogether wanting in it, and its color is white, owing 
to the absence of the reddish dust which is always present in 
the plagioclase. Its appearance in the hand-specimen is fresh 
and glassy, while under the microscope it possesses to a high 
* This Journal, Jan. 1886, p. 30. The word is here changed to the accepted form. 
