372 J. D. Dana on Serpentine Pseudomorphs 
true gneiss, but only sparingly. The feldspar of the rocks is 
generally whitish, though sometimes flesh-red; and, judging 
om the absence of strize on either cleavage surface, it is ortho- 
clase. Whitish mica (muscovite) is of rare occurrence. Minute 
zircons may often be found by searching in the syenytic rock 
with a lens. 
e rocks are generally very durable; but at the railroad 
cut in the village of Brewster, both the syenytic gneiss and the 
included hornblende rock are crumbling to a depth, in some 
gee of three or four feet, and this disaggregation appears to 
e in rapid progress. 
2. Ore-bed.—The magnetite of the ore bed is more or less 
mixed with chondrodite. In a portion of it, the magnetite 
greatly predominates, and the ore passes for massive magnetite. 
But through the larger part the chondrodite constitutes half or 
more of the mass, while much of the outer portion of the bed is 
correctly described as chondrodite containing, along with some 
other minerals, disseminated grains of magnetite. Massive 
chondrodite is the chief constituent of the refuse from the mine, 
and may be had there by the ton. 
The chondroditic rock and ore often contain disseminated 
chlorite; less generally, dark green or greenish-black horn- 
blende and grayish or brownish-gray enstatite; occasionally, 
disseminated white dolomite and brownish-black biotite; while 
orthoclase is not found, except in the enclosing syenyte. Mo- 
lybdenite is occasionally met with, and rarely apatite. A little 
pyrrhotite and chalcopyrite occur with some of the ore, and 
still less frequently pyrite. 
A small part of the rock is dolomite, with disseminated grains 
or crystals of chondrodite and occasional grains of magnetite. 
3. Veins in the ore-bed.—In small veins or nests in the ore- 
bed, the 
drodite, chlorite, and magnetite are often in excellent crystals, 
inches across. 
mentioned, but crystals of chondrodite are sometimes isolated 
mainly of coarsely crystallized chlorite, and others are filled 
with enstatite i 
of dolomite; but this dolomite is a filling, covering beautifu 
. 
on the walls of the little veins: yet the same dolomite often 
_ contains isolated erystals of chondrodite, magnetite or chlorite. 
