MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK Hil 
obscurely lenticular mass of magnetite, gently pitching with the 
rock structure to the northeast. The strike of the rock structure at 
or near the entrance to the mine is about north 78° west, and the 
dip is 16° a little east of north. Both strike and dip change, how- 
ever, from the entrance to the bottom of the mine, because of the 
situation of the ore body in the emerging end of an asymmetric syn- 
cline. According to the belief of the writer the corrugations are 
an inherited structure, caused by slight cross-folding during the 
intrusion of the basic Pochuck magma into previously folded Gren- 
ville strata; the ore, slightly later, adjusted itself to and followed 
the structures thus produced. Advantage has been taken of the roll- 
structure in mining, pillars of ore having been left as roof-supports 
at the crests of some of the rolls where the ore is thinnest. 
The mine is worked through an inclined shaft, or “slope,” sunk 
at an angle varying from 12° to 25° in places, following the length 
of the ore body and diverging from a straight line as much as 30° 
toward the bottom of the mine (see fig. 6). Drifts have been 
driven in either direction from the slope at various levels, the dis- 
tance across some of the levels being approximately 1000 feet. 
The slope has been sunk 3800 feet on the incline, which places 
the bottom of the mine well out under the lake and roughly between 
1000 and 1100 vertical feet below the level of the lake on the basis 
of an average inclination of 16°. The thickness of the ore body 
is somewhat difficult to estimate because of variations caused by the 
rolls; it will probably average somewhere in the neighborhood of 10 
feet. Although the mine has been worked since very early times and 
much ore has been hoisted, it is not yet exhausted, nor have the 
limits of the ore body been determined. 
Exploratory work carried on by the present operating company 
has outlined a large tonnage of ore. 
The Walls of the ore body. For a distance of 2300 feet the 
hanging wall of the Lake Slope is in part granite;1”> the granite 
is probably the Pochuck granite, although no petrographic studies 
have been made of it. The same granite appears at the surface at 
nearby points with included blocks and roof pendants of Pochuck- 
Grenville swamped in it. At 2300 feet the granite hanging wall in 
the slope gives way to granitized Pochuck-Grenville, which is heavily 
pegmatized in places. On the 2500-foot level the wall rock is 
slightly granitized Pochuck-Grenville carrying hornblende, biotite, 
a colorless monoclinic pyroxene, antiperthite, plagioclase of andesine 
125 Personal communication from D. H. Newland. 
