86 NEW YORK STATE MUSEUM 
for some 500 feet on the strike. Massive granite of probable 
Pochuck type forms part of the hanging wall and caps the ore body 
on the north end; the foot wall is granitized Pochuck-Grenville. 
Much coarse Pochuck dioritic pegmatite, and actinolite rock, may 
be found on the dumps. 
The ore occurs in an almost ideal lenslike form, judging from the 
shape of the walls of that portion which has been mined out; it is 35 
feet thick at the center, 125 feet wide (or high) in the plane of the 
lens along the strike, dips 80° southeast, strikes north 25° east, and 
pitches northeast. 
A small transverse fault cuts the ore body almost it its very 
beginning, offsetting the ore about 15 feet.” 
The lens of ore is split by a horse of country rock, but whether 
this is continuous or not it is impossible to determine. The mine 
has not been operated for many years. Thin sections of the ore 
exhibit the usual magmatic-replacement phenomena, the magnetite 
replacing very light-colored actinolite, which is very faintly pleo- 
chroic, and which grades into an almost colorless variety, essentially 
tremolite; a colorless pyroxene, less prominent, and quartz. Around 
each irregular corroded quartz grain, between them and the magne- 
tite, are replacement-aureoles of brownish green chlorite. The pres- 
ence of actinolite, much of which is essentially slightly ferruginous 
tremolite, as replacement-remnants in the ore, and the abundance of 
actinolitic rock on the dump, suggests that the Pochuck-Grenville 
rock replaced may have approached the character of an interbedded 
limestone, or at least that it was strongly calcareous in make-up. 
The size of the ore body and the general geological relations jus- 
tifies the belief that proper additional exploratory work might prove 
the existence of a body of magnetite in very considerable quantity. 
The Brennan mine. About 1600 feet west of the Crawford 
mine a shaft was sunk 20 feet through ore nearly vertical in dip 
and about 10 feet in thickness, in order to prospect this body of 
magnetite, which is apparently one of the isolated occurrences. 
Twenty feet southwest of the first prospect pit and in the same line 
of strike, another hole was driven which discovered nothing but 
drift, nor did the dip-needle indicate the presence of ore. The fault 
which cuts the southern end of the Crawford ore body, would if 
extended cut likewise the ore in the Brennan pit. It is believed that 
the abrupt termination of the ore in the Brennan pit is in part due 
129 The ore has been mined out at this point, but the former shape is pre- 
served by the walls, and the offset may be readily seen. 
