104 J. D. Dana—Origin of the Rocks of the Cortlandt? Series. 
Other constituents of these rocks are frequently apatite (which 
is often in unusual proportions), and more or less magnetite, pyr- 
rhotite and pyrite (the pyrite mostly confined to the soda-gran- 
ite and dioryte). In the many slices (over 60) which I have 
microscopically examined, I have found no glassy or unindividal- 
ized material, and no appearances of a fluidal character, except 
that of broken crystals or crystalline grains. 
o the description of the noryte before given I here add the 
results of a careful chemical analysis made in the laboratory of 
the Sheffield Scientific School of Yale College (under Professor O. 
D. Allen) by Mr. M. D. Munn of that School. The specimen 
was from the northern half of Montrose Point, on the Hudson. 
Sid. AlO, FeO; FeO MnO MgO CaO Na.O K.O H,z0 
1. 55°28 16°31 069 757 0-40 5°05 7:52 410 2°05 058 —99°55 
2. 55°40 16°44 0°85 751 039 5°05 749 4:03 2°00 [0°58]—99°73 
Mean 55°34 1637 O77 754 040 505 751 4:06 2°03 0°58 =—99-65 
The evidence already presented with regard to the Cort- 
landt rocks sustains the conclusion, as I believe, that to 4 
large extent at least they are of metamorphic origin; but that 
in the metamorphic process the original beds were rendered 
(through the heated moisture concerned in the metamorphism), 
more or less plastic or mobile, so that they thus lost all, or the 
most of, their original bedding, and that, as a consequence. 
they formed in some places intrusive dikes or veins intersect- 
ing other rocks having all the characteristics of eruptive rocks. 
