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ie) NEW YORK STATE MUSEUM 
composition, very little quartz, which occurs interstitially and in 
poikilitic fashion in the hornblende, and a little magnetite. 
Pochuck-Grenville, more or less modified by granitization and 
pegmatization, forms both walls for the remainder of the distance 
to the bottom of the mine. At the east end of a drift on the 2800- 
foot level the hanging wall is very heavily pegmatized, carrying a 
green, slightly pleochroic monoclinic pyroxene, bluish green horn- 
blende, quartz, strongly sericitized plagioclase of about andesine 
composition, fresh orthoclase which has margins of albite; epidote, 
disseminated magnetite which cuts and encroaches upon the silicate 
minerals, and considerable apatite. The drift at this point is in or 
very close to the “ slip-zone ” described further on. 
Footwall samples taken from the main slope at the 3100 and 3200- 
foot levels are strongly foliated in structure and contain a very 
light-colored pink to slightly greenish, pleochroic and monoclinic 
pyroxene (“ clino-hypersthene ’’), a light-green non-pleochroic mono- 
clinic pyroxene (coccolite), much biotite with meta-poikilitic habit, 
andesine, quartz and a little magnetite (see plate 9; figure 3). It 
is essentially slightly granitized Pochuck-Grenville with an inherited 
structure. 
It will thus be seen that the wall rock of the Lake mine, and 
probably of the Sterling as well, is in part granitized Pochuck-Gren- 
ville, in part pegmatized Pochuck-Grenville, and in part Pochuck 
granite, all involved with streaks and stringers of pegmatite. The 
strongly inequigranular habit, the mode of aggregation, association 
and marginal relations of the minerals, the great range in the com- 
positions of the feldspars, the strongly foliated structure, the evi- 
dence of injection, and the manner in which the magnetite encroaches 
upon and cuts the other minerals indicate some other and much 
more complex origin than a simple igneous one, for these rocks. 
The “slip-zone.” A zone of mixed rock and disseminated ore, 
approximately 150 feet in width and striking a few degrees from 
direct north-south, cuts the northeast edge of the Lake ore body 
and presumably cuts the east edge of the Sterling ore body also, as 
at present defined and shown on the map of the Sterling group 
(fig. 6). 
This zone has been called the “slip-zone” by Mr Charles Rees, 
superintendent of the Ramapo Ore Company; its location is only 
approximately shown on the map, since the exact trend and width 
have not yet been determined. The general direction shown is prob- 
ably but a few degrees in error however, and the estimated width is 
