The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1922-07-06

tory of the earth and its inhabitants
: that treats of the rocks and materials
of the earth. and the agencies and
various processes which have been
involved in their formation and ar
rangement. Another phase of it in
terprets by the rocks, their fossil con
tents and structural attitudes and
the various stages through which the
earth and it's living inhabitants have
passed.
Geological Classification.
The rocks and materials of the
earth are conveniently classed in
three groups:
The igneOus rocks make up the first
group and owe their origin to the
cooling of molten slag-like magma
made up of a mineral complex that is
forced into and through the earth's
hardened outer crust. There are or
course a large number of variations
in these igneous rocks but there are
three distinct classes into which they
can be grouped. The first group are
fine grained and show few crystals
l
entirely pierced the crustal covering
and upon being suddenly exposed to
the air has chilled so quickly as to
prevent the arrangements of the var
ious minerals into crystals. Basalt is
a common rock that is truly represen-
tative of this type of igneOus occur
renee.
Opposed to the above occurrence is
the formation of another type of ig-
neOus rock Large reservoirs of mag
ma slowly eating and absorbing their
way through the everything layers of
the earth's crust often fail to reach
the surface before losing their heat
This magma receives no sudden chill
but has ample time to cool and as a
consequence the various minerals
separate and all segregate into well
defined crystals with certain charac-
teristics peculiar to that mineral. The
commonly known granite represents
an excellent type of this igneous rock
occurrence.
The third igneOus type represents
an intermediate stage between the
first two types and provides a type of
rocks which have a fine grained tex
ture similar to the basalt described
above but which also contain crys-
tails or phenOcrysts. These rocks are
properly called porphyries. They are
usually found as bikes, sills or feeders
to the flows of the first type of igne-
Gus rock.
Second Great Group.
Sedmentary rocks make up the
second great group These rocks are
formed from various sized fragments
of all kinds of rock material worn and
broken away by hundreds of forces
from the ever-present land masses
which we call continents This ma
terial once detached is carried by the
wind OF by the water OF countless
streams toward the oceans. Some of
it may be deposited in the widening
of the river or in lake, some may
travel along a mountain stream to
be deposited at the base of the noun
tain slope in the form of an alluvial
fan or cone. But much the greater
part will finally reach the sea there
to be sorted and left. The coarser
sediments are dropped first and the
finer materials carried farther out,
thus three types of material are fin
ally graded out by this water sorting
The gravel deposited close by the
shore eventually becomes compacted
and cemented into a rock formation
called conglomerate. Sand grains de-
posted farther from shore likewise
become sandstones. The finest par
ticles of dust or silt which are carried
farthest into the sea, change in a sim
liar fashion from mud to shale. Be
yond these deposits where sediments
from the land fail to reach these
ocean depths myriads of invertebrate
animals live and die. Most of them
have shells of calcium carbonate
Qime) that in due time become COM
pacted and cemented into a sedimen-
'tary rock called limestone. There
are of course all gradations possible
between these types of rocks.
Particles of magma blown from
erupting volcanoes cool in air and
may be carried by the air currents to
settle in water bodies such as lakes,
rivers and seas. thus developing a
true sedimentary bed from volcanic