Northern Wisconsin advertiser. [volume] (Wabeno, Wis.) 1898-1925, 1902-09-25
ROCKS MADE BY FIRE.
Many Famous Geologic Terms Elk
planned by Mining journal.

The igneouS rocks come first be-
cause they have been the originals.
BY igneous rocks we mean those that
have been thoroughly fused or melted,
like lavas, porphryies, etc. The heat
need not have been a dry heat, like
that of furnace, but an equeo-igneous,
or fire and water or steam heat; suf-
ficient in some cases to reduce them
to a pasty condition; in others, like
volcanic lavas, to fluid one. Even
lavas, pouring from Vesuvius, show
evidence of an aqueous, as we'll as of
an igneous condition, for they give off
volumes of steam. Metamorphic rocks
are those that have been altered by
heat lin place." to semiplastic con-
dition, like some GRANTEES, or simply
recrystalized like marbles, or only par
TALLY crystalized, like quartzites.
The igneous rocks are the originals
from which all others nave been d.
rectly or indirectly derived. Examine
any one of the thousands of feet of
sandstone that underlie our prairies
and build up our foothills and you will
find them either composed of large
or small fragments of granite or of
cry staline grains derived from the con-
stituent minerals of granite, viz,
quartz and feldspar, or else from sim
lar material derived from igneous
lavas. Limestone is almost the only
exception, being an organically
formed rock, yet If We were to go back
into the ultimate origin and history of
limestone, we might find that even the
lime utilized by the corals and other
organisms was derived from the ma
terial of some igneous rocks We
were reborn world before we became
born again part by water
bikes, meaning walls" like the
dixie walls of Holland built to Keep
back the sea, are formed by molten
lava penetrating assures in the rocks
and solidifying in them When tho
surrounding rock is softer than the lava
filled assure, and is eroded away, the
lava stands up in relief above the sur
face of the country like a wall or dixie.
bikes are elongated, narrow bodies of
all, from an inch in thickness and d
| few feet in length, to others a thou
sand or more feet across and miles in
| length. The region about Trinidad, in
Southern Colorado, is a network of
lava bikes, which emanating from a
great volcanic laccolitic center called
the Spanish Peaks, traverse the whole
region and the surrounding plains, the
lava cropping up among the soft shales
of the prairies and running across il
in low walls for many miles. bikes
of porphyry and other eruptive rocks
are common throughout the mountains
sometimes appearing like dark, narrow
! ribbons traversing the face of a cliff
or forming the prominent top or peal
of mountain like Mount Lincoln, fol
example, or forming the zone contain
ing precious metal, as at Cripple
| Creek.
| Sheets" are bodies of relatively
great lateral or horizontal extent com
pared with their thickness. They are
either surface flows which may be az
terward buried by sediments or else
are intruded between other strata. In
the latter case they may be called laco-
lithic if very thick and lenticular in
shape. Examples of these laccolites
are very common in Colorado and the
west The Spanish peaks, before al
luded to, are great laccolites, that is,
great CONCEALED reservoirs of lava, the
lava of which originally came from
below through assures, but not
having power enough to break through
the heavy everything stratifed rocks,
and pour out in lava streams on the
surface of the country or on the bot
tom of the sea, contented itself with
arching up the everything strata and
filling the cavity so formed with its
own molten mass. Later by erosion
the OVERLAPPING strata may be re-
moved and disclose the huge thick
mass of lava buried below and finally
leave 1t as great mountain mass of
igneous rock high above the surface
of the country with a girdle of erod-
ed sedimentary rocks tipped up all
around it,
hougnly tubular masses, such as
might chill in the conduit of a vol
cano are called "necks." The chilled
stopper or plug of the crater of
volcano after the eruption is over
and past, like the accolite, is thor
oughly crystalline and usually very
compact
Irregular, projecting, rounded
bodies are called bosses" such as
granite bosses, porphyry bosses, etc.
Enormous masses of crystalline
rocks, like granite, covering hundreds
of square miles, have fused their way
upwards by melting into their sub
stance everything rocks. OF their ex-
istance we should know little IL they
were not uncovered by great erosion.
Igneous rocks are characteristicall
massive, as contrasted with the STRAIT.
flied structure Of sedimentary rocks.
The term "eruptive" means that the
rocks have come from below.
A distinction has been made be-
tween those like granite that have
crystallized deep within the earth
(the plutonic) and those poured out