Fig. 1 Rock from dump, Mahopac mine; light polarized, nicols crossed, 
magnification 65 diameters. 
Showing chondrodite (light gray, patchy area), clinochlore, (white to dark 
gray, twinned crystals) phlogopite (resembles the clinochlore in the photo- 
micrograph) and magnetite (black). 
The result of the complete reorganization and silication of an interbedded 
Grenville limestone by contact action. 
Fig. 2 Rock from the “slip-zone,” 2500 foot level, Lake mine. Light 
polarized, nicols crossed, magnification 35 diameters. Actinolite, with roughly 
parallel arrangement, and feldspar, with a little magnetite, epidote and titanite. 
Step-faulted, but all weaknesses thoroughly healed. Judged to be a pegma- 
tized amphibolite, related to Pochuck-Grenville. The “slip-zone” is a Pre- 
cambrian fault-zone, “post-rolls” and “pre-ore” in time relation. 
Fig. 3. Foot wall, Lake mine, 3100 feet down the slope. Light polarized, 
nicols -crossed, magnification 35 diameters. Granitized Pochuck-Grenville, 
with strongly foliated structure. Essentially a Grenville schist which has 
been thoroughly soaked with the dioritic facies of the Pochuck magma, and 
granitized by lit-par-lit injections, retaining the schistose habit of the original. 
Now a grano-diorite in its general composition. It carries a pinkish pleo- 
chroic monoclinic pyroxene (clino-hypersthene), a green pyroxene, like 
coccolite, much biotite, plagioclase of andesine composition, a little alkalic 
feldspar, quartz, a little magnetite and apatite related to the injection or 
soaking period. 
Fig. 4. A garnet-bearing rock from the Lake mine, specimen taken from 
the dump. Ordinary light, X 35 diameters. Garnet (rough, speckly gray), 
green pyrozene (rough, with cleavage) and magnetite (black). 
The green pyroxene resembles coccolite, and the general make-up of the 
rock suggests a metamorphic, rather than an igneous origin. 
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