Orleans County monitor. [volume] (Barton, Vt.) 1872-1953, 1880-03-22
SCIENCE FOR BOYS.


SCIENCE FOR BOYS.
A rock is any bed, layer or mass of
the material of the earth's crust. The
term, in common language, is confined
to the solid rock. But in geology it is
often applied to kinds. so as to include
granite, limestones, conglomerates, sand
stones, clay-slates, and the like solid
rocks; gravel beds, clay beds, allumi-
mum and any loose deposits, whenever
arranged in regular layers or strata as
a result of natural causes. Rocks are
composed of minerals. But these min
erals may be of mineral or organic ORR
gin. The material of all the great lime
stone formations, is derived from the re-
mains of plants of animals, ground into
calcareous earth by the sea and con-
solidated, just as corals are now ground
up and worked into great coral reef
rocks in the West Indies and the Pacific
Ocean.
In other cases only a small part of
rock is organic, the rest being of min
eral origin. Such rocks usually contain
distinct remains of shells of corals that
have contributed to their formation
these relics, whether plants or animals,
are called fossils, and the rocks are said
to be fossiliferous. They are also call
ed petri6cations, though not always pet
rifed.
The material of mineral origin in
cludes all that is not directly of organic
origin, ,sall the sand, gravel, etc., derived
from the trituration or wear of other
rocks; the material from chemical de-
composition, like limestones, or from
volcanic action. like lavas and trapp Eor
basalt.
Rocks are conveniently divided into
fragmental and crystalline. Rocks that
are made up of pebbles, sand. or the
particles of sand, and even of clay, be-
ing strictly fragments broken from the
rocks of the globe, either deposited as
sediment in moving waters, or accumula-
ted through other means, as ordinary
conglomerates. sandstones, clay rocks,
tufas and nearly all limestones.
The larger part of the rocks here
mentioned are made of sedimentary ma
terial,-that is, material deposited as
sediment by marine or fresh water, and
hence called sedimentary rocks, consist
ing of layers spread out one over the
other.
Granite, granular crystalline rock,
consisting of quartz feldspar and mica
having no appearance Of layers in the
arrangement of the mica or other ingre-
dients. The mica is in scales. usually
white or black, or brownish, easily sep
arabic into thinner elastic scales by
means of the points of knife; the
quartz is usually grayish white, CLASSY,
and without any appearance of cleav-
age; the feldspar is commonly whitish
or fesh-colored, less CLASSY than the
quartz, and showing fiat. polished
cleavage surface in one or two direc-
tions. An average granite is composed
of silica 72.O7, alumina 14.81, pro-
toxide and sesquioxyde of iron 2-52
magnesia 0-33, lime 63, potash IL,
soda 2-79, water 1-O9-100-35.
Porphyritic granite has the feldspar
distributed in distinct crystals which
appear as rectangular whitish blotches
on surface of fracture. Hornblende
granite contains black scales or grains
of hornblende, besides the mica There
are also other kinds Of granite that may
be described hereafter.
| Gneiss, like granite, but with mica
more or less distinctly in layers. A
gneissoid granite is rock intermediate
between granite and gneiss. Gneiss
breaks most readily in the direction of
the mica layers and this affords slabs,
or schistose, instructure.
Mica Schist.-The same constituents
as granite and gneiss, but with more
quartz and less feldspar, and much more
mica-therefore glistening in luster
slaty or very schistose in structure
breaking into thin slabs. Garnets are
often found in this rock.
Argillyte.-A fine grained, slaty rock
of various colors. grayish to black and
sometimes greenish, reddish, purplish
The evenly-splittiug kinds are roofing
slate and writing slate. 1t consists usu'
ally of pulyerized quartz and feldspar
with sometimes little chlorite. Ano'
/ ther kind contains no alkalies and hence
no feldspar. The common embedded
minerals found in this rock are andalu
: site. staurolite, garnet. and phyllite.
Now, boys, don't get discouraged
remember that the richest mines lay
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