MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 53 
from the rock (Pochuck-Grenville) which the magnetite, by mag- 
matic processes, replaced; some of the feldspar and the ferromag- 
nesians have certainly been so derived. The evidence for this 1s 
based on the distribution, mode of occurrence and association of 
these rocks, and on the fact that petrographic study shows them to 
contain a vast amount of quartz in extremely coarse grains of uni- 
form optical orientation, which acts as a matrix for corroded and 
sericitized fragments and bunched aggregates of feldspar (chiefly 
plagioclase), corroded and altered ferromagnesians, and corroded 
and altered complex fragments, whose distribution and whose mar- 
ginal relations to the quartz are not such as to suggest consecutive 
crystallization from the same parent magma, but which behave as 
xenolithic fragments more or less affected by the aqueo-igneous 
solutions which gave rise to the quartz. 
This granite, closely related to the magnetites and an end-phase 
of them, involved to a greater or less degree with the Pochuck- 
Grenville, judged to be the very ultimate differentiation product of 
the Pochuck magma; corrosive, insidious and pervasive in character, 
and much more extensively distributed than commonly supposed, 
has been called by the writer the “Pochuck granite.’ Plate 2, 
figure 4, plate 3, figure 2, plate 4, figure 4 and plate 5, figure 4 
illustrate some of the characteristics of this granite. Much of the 
feldspar, and essentially all of the ferromagnesian minerals, are 
simply swamped, sericitized, epidotized, uralitized and carbonated 
remnants of the rock through and into which the final mother liquor 
found its way. 
The rocks associated with the ore bodies exhibit all gradations 
from unmodified Pochuck-Grenville, to granitized, highly grani- 
tized, and intensely granitized products and finally granite. 
Canada Hill granite. There are other granite masses, not re- 
lated to the magnetite at all, of sufficient extent to be considered 
individual units, which cut the Pochuck and its various modifica- 
tions and which are therefore very distinctly later. From the field 
occurrences, extent and lithologic similarity these granites may be 
tentatively correlated with the Canada Hill granite*°° of the West 
Point quadrangle. A granite of this character of considerable 
extent occurs about one-half of a mile north of the O’Neill mine, 
well exposed along the highway leading to Lake Mombasha; its 
associated syntectic may be found at Round pond about 1%4 miles 
100 Berkey, Charles P., & Rice, Marion. Geology of the West Point Quad- 
rangle. N. Y. State Mus. Bul. 225-226. 
