Clarksville weekly chronicle. (Clarksville, Tenn.) 1873-1890, 1879-08-09

w AOW IfihC up tIAO NACpdA tihOIll
of the
ROCKS.
And perhaps it would be well to
premise, that rocks differ from min
erals in being heterogeneous in their
constitution, while minerals are
homogeneous Rocks may be con-
sidered mineralogical compounds,
while minerals are the correspond
ing elements ; thus, Quartz is a
mineral, while Granite, consisting
of Quartz, Feldspar and Mica, is a
Rock.
Here are a hundred specimens of
Granite, from various localities,
some coarse grained, others fine. In
some, the individual crystals of the
compound minerals are large and
distinct, in others small and OBJ
scure the relative amounts also of
the constituents differ greatly. These
can be easily distinguished one from
another by their well-known char
acteristics of color, cleavage, hard
ness, etc. Numerous splendid spec
linens from the neighborhood of
Philadelphia, are here seen, in
which the distinction can easily be
recognized by the most inexpe-
rienced. The peculiar type known
as Graphic Granite is finely repre-
sented, from the neighborhoods Of
Baltimore, Md, and Wilmington,
Del, as also from other places. A
certain arrangement of the CLASSY
quartz crystals in the midst of, and
contrasting with the more fiesh-col-
ored feldspar, produces upon the
surface of the rock an appearance
somewhat resembling Arabic or hi
eroglyphic a0ritiagj hence the
name. Some very beautiful Gran
ties are red, owing to the presence,
often in large crystals, of Red Field
spar.
The gradation from Granite to
Gneiss is here well shOwn-there
are 80 specimens of the latter. Gneiss
has been called ''stratified Granite,"
the same constitution, but a
more lined or laminated aspect. 1t
is undoubtedly the result of meta
and expresses (if Gran
ite be considered to proceed from
this kind of action too, which is
now generally accepted) metamor-
phic change less complete than that
in Granite. Syenite and Syenitic
Granite have their representatives,
in which the mineral Hornblende
is either substituted for Mica, or
to the original constit-
uents.
Nearly related to the preceding in
are Mica Slate and
Mica Schist, both characterized by
the predOminance of Mica. One
fine specimen of the Slate comes
from Georgia, another from near
in the latter the
lines of cleavage are beautifully
distinct, and there is also to be no
ticed the Interpolation of layers of
of Lime. Many of the
Schists are literally packed with
Garnets adding greatly to the in
tereSt of the specimen.
Two drawers contain 80 or mcle
specimens several of 4
the micaceous variety some be-
longing to the POtsdam period,
some to the Hamilton Red Sand
stone and gray purple, yellow and
black /; some containing ripple
marks, others vegetable impress
sions (as stigmaria and fucoids), still
others, Calcite and Pyrites. Here
IS some white Silicious Sand from
Lake Borgne, Mexican Gulf Coast
here are three bottles of beautifully
sands from the Plastic
Clay formation, Purbeck, England.
And here are three bottles more,
containing yellowish brown sand
rom the Sahara Desert, presented
oy Mrs. w. w. Legare, now of Wal
naIla, South Carolina.
Just beyond, we find a tray of "a
splendid conglomerates, pudding
stones, as they are generally called.
One is particularly fine-large,
rounded pebbles, oemented together
by red oxide of Iron. This speci-
men was placed in our hands by
Mr.. Stewart, some years since, with
the remark that it was found in the
bed of river in Virginia. 1t Is
therefore of recent origin, geolog-
Ically.
We must not omit to mention the
three very interesting specimens of
ItacOlumite, or Flexible Sandstone,
from North Carolina, one nearly
two feet in length. It is capable OF
to a considerable degree
without breaking. 1T is slightly
to which circumstance
its fiexibility has been ascribed. We
do not think the small amount of
Mica present can be taken as sgffi-
oient and satisfactory explanation
of the phenomenon. It is more
probably due to some unique mode
of molecular aggregation. Its par
ticles are loosely held together, al
lowing therefore of considerable
without permanent loss
of cohesion. Itacolumite is found
in Brazil we believe that it is
known in but one locality in the
United States.
Here is a tray containing Clays of
many colors Kaoltn, o white and
pure form, from Saxony q Yarie-
gated Argyle from Columbia, South
Pipe Clay, and Potter's
Clay; Ferruginous Clay and Red
Chalk several specimens of Lith-
omarge "a compact species, from
Rochlitz, Saxony), purple, reddish,
white. Many of these specimens