Page 637

APPENDIX -MICROSCOPIC LITHOLOGY.
637T
APPENDIX.
MICROSCOPIC LITHOLOGY.
BY CHA1RLES E. WRIGHT.
[NOTE. -The following descriptions are of a small number of crystalline rocks
selected from the
large mass of material on hand. as rmost difficult to determine, or as having
a special importance.
The numbers are the same as given in the body of the report, and the original
specimens will be
found in the survey collections, when distributed. A few of Mr. Wright's
descriptions have been
made use of in the foregoing pages, but the descriptions of crystalline rocks
there given are
nearly alwaays wholly my owln. It is a matter of regret that the funds were
not available for micro-
scopic examination of a full suite of the Central Wisconsin rocks. R. D.
I.]
501. Silicions Hornhlende-Schist. HuiRoNIAN?       Black ricer, Jackson county,
north 1ine Sec. 14, T. 212 R. 4 W. Light-greenish-black; very fine-grained;
crystalline
texture; conchoidal fracture; hard and compact.  With the lens, minute grains
of silica
are plainly visible, but the ingredient minerals cannot be distinguished.
Under the mi-
croscope, in the polarized light, a thin section of the rock presents a very
pretty field,
and is composed of small fragments of amphibole, minute grains of quartz,
and a few
scattered leaves of chlorite. From the structure it is evident that the amphibole
formed
after the quartz, since the former encloses grains of the latter.
757. Granite. HURONI tN?       Village of Montello, Marquette county, S.
W. qr.
Sec. 9, T. 15, R. 10 E. Pale flesh-color, dotted with a few dark patches
of mnica. The
facets of felspar are easily recognized. Traversing the specimen is a thin,
light-green-
isle seam of what appears to be epidote. Under the microscope, in the polarized
light,
the coarse fragments of orthoclase apparently constitute more than one-half
the en-
tire section. An occasional twin crystal of felspar after the Carlsbad form
may be
seen. The grains of quartz are mostly very small and angular, and are frequently
enclosed within tbe felspar. With a power of 500 diameters are visible, in
the quartz,
fluid inclusions; the absence, however, of any glass or stone-filled cavities
will no doubt
refer the rock to a metamorphic origin.
758. Argillo-chloritic Schist. HURONIAN? Village of Montello, MVar-quette
Counity,
S. TV. qr. Sec. 9, T. 15, R. 10 E. Grayish-green; fine-grained texture; partially
decom-
posed; cleaves readily into irregular plates; in the joints it is often ocherous;
under the
microscope the pale greenish leaves of chlorite are plainly visible; also
minute grain-s of
silica and a few scales of hematite.