Wilkie Collins - "Antonina"

Georgina Pell Curtis - "The Interdependence of Literature"

Maxim Gorky - "Mother"

Aristotle - "The Poetics"

New Philadelphia Book Publisher Highlights Local Talent
Book and Publishing News from Publishers Newswire(tm)

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PHILADELPHIA, Pa. -- The Philadelphia literary world will celebrate the launch of two new players today, April 10th: Kay Square Press, a new publishing company focused on Philadelphia-area artists, their stories, and their art; and Kay Square's first release, 'With the Rich and Mighty: Emlen Etting of Philadelphia' (ISBN: 978-0-9815129-0-7), a critical biography by Kenneth C. Kaleta.

FlatSigned Press Alleges Don Imus Remarks Damage Legacy of President Gerald R. Ford
NEW YORK, N.Y. -- Nathan Yungerberg, an accomplished model scout and professional child photographer is launching a nation-wide casting call to find the cover model for his highly anticipated book release, 'The Model Child: A Parents Guide to the Child Modeling Industry' (ISBN: 978-0-9817018-0-6).

Books: The Elements of Geology

W >> William Harmon Norton >> The Elements of Geology




PHYSIOGRAPHIC EFFECTS OF INTRUSIVE MASSES. We have already seen
examples of the topographic effects of intrusive masses in Mount
Hillers, the Spanish Peaks, and in the great mountain ranges
mentioned in the paragraph on regional intrusions, although in the
latter instances these effects are entangled with the effects of
other processes. Masses of igneous rock cannot be intruded within
the crust without an accompanying deformation on a scale
corresponding to the bulk of the intruded mass. The overlying
strata are arched into hills or mountains, or, if the molten
material is of great extent, the strata may conceivably be floated
upward to the height of a plateau. We may suppose that the
transference of molten matter from one region to another may be
among the causes of slow subsidences and elevations. Intrusions
give rise to fissures, dikes, and intrusive sheets, and these
dislocations cannot fail to produce earthquakes. Where intrusive
masses open communication with the surface, volcanoes are
established or fissure eruptions occur such as those of Iceland.

THE INTRUSIVE ROCKS

The igneous rocks are divided into two general classes,--the
VOLCANIC or ERUPTIVE rocks, which have been outpoured in open air
or on the floor of the sea, and the INTRUSIVE rocks, which have
been intruded within the rocks of the crust and have solidified
below the surface. The two classes are alike in chemical
composition and may be divided into acidic and basic groups. In
texture the intrusive rocks differ from the volcanic rocks because
of the different conditions under which they have solidified. They
cooled far more slowly beneath the cover of the rocks into which
they were pressed than is permitted to lava flows in open air.
Their constituent minerals had ample opportunity to sort
themselves and crystallize from the fluid mixture, and none of
that mixture was left to congeal as a glassy paste.

They consolidated also under pressure. They are never scoriaceous,
for the steam with which they were charged was not allowed to
expand and distend them with steam blebs. In the rocks of the
larger intrusive masses one may see with a powerful microscope
exceedingly minute cavities, to be counted by many millions to the
cubic inch, in which the gaseous water which the mass contained
was held imprisoned under the immense pressure of the overlying
rocks.

Naturally these characteristics are best developed in the
intrusives which cooled most slowly, i.e. in the deepest-seated
and largest masses; while in those which cooled more rapidly, as
in dikes and sheets, we find gradations approaching the texture of
surface flows.

VARIETIES OF THE INTRUSIVE ROCKS. We will now describe a few of
the varieties of rocks of deep-seated intrusions. All are even
grained, consisting of a mass of crystalline grains formed during
one continuous stage of solidification, and no porphyritic
crystals appear as in lavas.

GRANITE, as we have learned already, is composed of three
minerals,--quartz, feldspar, and mica. According to the color of
the feldspar the rock may be red, or pink, or gray. Hornblende--a
black or dark green mineral, an iron-magnesian silicate, about as
hard as feldspar--is sometimes found as a fourth constituent, and
the rock is then known as HORNBLENDIC GRANITE. Granite is an
acidic rock corresponding to rhyolite in chemical composition. We
may believe that the same molten mass which supplies this acidic
lava in surface flows solidifies as granite deep below ground in
the volcanic reservoir.

SYENITE, composed of feldspar and mica, has consolidated from a
less siliceous mixture than has granite.

DIORITE, still less siliceous, is composed of hornblende and
feldspar,--the latter mineral being of different variety from the
feldspar of granite and syenite.

GABBRO, a typical basic rock, corresponds to basalt in chemical
composition. It is a dark, heavy, coarsely crystalline aggregate
of feldspar and AUGITE (a dark mineral allied to hornblende). It
often contains MAGNETITE (the magnetic black oxide of iron) and
OLIVINE (a greenish magnesian silicate).

In the northern states all these types, and many others also of
the vast number of varieties of intrusive rocks, can be found
among the rocks of the drift brought from the areas of igneous
rock in Canada and the states of our northern border.

SUMMARY. The records of geology prove that since the earliest of
their annals tremendous forces have been active in the earth. In
all the past, under pressures inconceivably great, molten rock has
been driven upward into the rocks of the crust. It has squeezed
into fissures forming dikes; it has burrowed among the strata as
intrusive sheets; it has melted the rocks away or lifted the
overlying strata, filling the chambers which it has made with
intrusive masses. During all geological ages molten rock has found
way to the surface, and volcanoes have darkened the sky with
clouds of ashes and poured streams of glowing lava down their
sides. The older strata,--the strata which have been most deeply
buried,--and especially those which have suffered most from
folding and from fracture, show the largest amount of igneous
intrusions. The molten rock which has been driven from the earth's
interior to within the crust or to the surface during geologic
time must be reckoned in millions of cubic miles.

THE INTERIOR CONDITION OF THE EARTH AND CAUSES OF VULCANISM AND
DEFORMATION

The problems of volcanoes and of deformation are so closely
connected with that of the earth's interior that we may consider
them together. Few of these problems are solved, and we may only
state some known facts and the probable conclusions which may be
drawn as inferences from them.

THE INTERIOR OF THE EARTH IS HOT. Volcanoes prove that in many
parts of the earth there exist within reach of the surface regions
of such intense heat that the rock is in a molten condition. Deep
wells and mines show everywhere an increase in temperature below
the surface shell affected by the heat of summer and the cold of
winter,--a shell in temperate latitudes sixty or seventy feet
thick. Thus in a boring more than a mile deep at Schladebach,
Germany, the earth grows warmer at the rate of 1 degrees F. for
every sixty-seven feet as we descend. Taking the average rate of
increase at one degree for every sixty feet of descent, and
assuming that this rate, observed at the moderate distances open
to observation, continues to at least thirty-five miles, the
temperature at that depth must be more than three thousand
degrees,--a temperature at which all ordinary rocks would melt at
the earth's surface. The rate of increase in temperature probably
lessens as we go downward, and it may not be appreciable below a
few hundred miles. But there is no reason to doubt that THE
INTERIOR OF THE EARTH IS INTENSELY HOT. Below a depth of one or
two score miles we may imagine the rocks everywhere glowing with
heat.

Although the heat of the interior is great enough to melt all
rocks at atmospheric pressure, it does not follow that the
interior is fluid. Pressure raises the fusing point of rocks, and
the weight of the crust may keep the interior in what may be
called a solid state, although so hot as to be a liquid or a gas
were the pressure to be removed.

THE INTERIOR OF THE EARTH IS RIGID AND HEAVY. The earth behaves as
a globe more rigid than glass under the attractions of the sun and
moon. It is not deformed by these stresses as is the ocean in the
tides, proving that it is not a fluid ball covered with a yielding
crust a few miles thick. Earthquakes pass through the earth faster
than they would were it of solid steel. Hence the rocks of the
interior are highly elastic, being brought by pressure to a
compact, continuous condition unbroken by the cracks and vesicles
of surface rocks. THE INTERIOR OF THE EARTH IS RIGID

The common rocks of the crust are about two and a half times
heavier than water, while the earth as a whole weighs five and
six-tenths times as much as a globe of water of the same size. THE
INTERIOR IS THEREFORE MUCH MORE HEAVY THAN THE CRUST. This may be
caused in part by compression of the interior under the enormous
weight of the crust, and in part also by an assortment of
material, the heavier substances, such as the heavy metals, having
gravitated towards the center.

Between the crust, which is solid because it is cool, and the
interior, which is hot enough to melt were it not for the pressure
which keeps it dense and rigid, there may be an intermediate zone
in which heat and pressure are so evenly balanced that here rock
liquefies whenever and wherever the pressure upon it may be
relieved by movements of the crust. It is perhaps from such a
subcrustal layer that the lava of volcanoes is supplied.

THE CAUSES OF VOLCANIC ACTION. It is now generally believed that
the HEAT of volcanoes is that of the earth's interior. Other
causes, such as friction and crushing in the making of mountains
and the chemical reactions between oxidizing agents of the crust
and the unoxidized interior, have been suggested, but to most
geologists they seem inadequate.

There is much difference of opinion as to the FORCE which causes
molten rock to rise to the surface in the ducts of volcanoes.
Steam is so evidently concerned in explosive eruptions that many
believe that lava is driven upward by the expansive force of the
steam with which it is charged, much as a viscid liquid rises and
boils over in a test tube or kettle.

But in quiet eruptions, and still more in the irruption of
intrusive sheets and masses, there is little if any evidence that
steam is the driving force. It is therefore believed by many
geologists that it is PRESSURE DUE TO CRUSTAL MOVEMENTS AND
INTERNAL STRESSES which squeezes molten rock from below into
fissures and ducts in the crust. It is held by some that where
considerable water is supplied to the rising column of lava, as
from the ground water of the surrounding region, and where the
lava is viscid so that steam does not readily escape, the eruption
is of the explosive type; when these conditions do not obtain, the
lava outwells quietly, as in the Hawaiian volcanoes. It is held by
others not only that volcanoes are due to the outflow of the
earth's deep-seated heat, but also that the steam and other
emitted gases are for the most part native to the earth's interior
and never have had place in the circulation of atmospheric and
ground waters.

VOLCANIC ACTION AND DEFORMATION. Volcanoes do not occur on wide
plains or among ancient mountains. On the other hand, where
movements of the earth's crust are in progress in the uplift of
high plateaus, and still more in mountain making, molten rock may
reach the surface, or may be driven upward toward it forming great
intrusive masses. Thus extensive lava flows accompanied the
upheaval of the block mountains of western North America and the
uplift of the Colorado plateau. A line of recent volcanoes may be
traced along the system of rift valleys which extends from the
Jordan and Dead Sea through eastern Africa to Lake Nyassa. The
volcanoes of the Andes show how conspicuous volcanic action may be
in young rising ranges. Folded mountains often show a core of
igneous rock, which by long erosion has come to form the axis and
the highest peaks of the range, as if the molten rock had been
squeezed up under the rising upfolds. As we decipher the records
of the rocks in historical geology we shall see more fully how, in
all the past, volcanic action has characterized the periods of
great crustal movements, and how it has been absent when and where
the earth's crust has remained comparatively at rest.

THE CAUSES OF DEFORMATION. As the earth's interior, or nucleus, is
highly heated it must be constantly though slowly losing its heat
by conduction through the crust and into space; and since the
nucleus is cooling it must also be contracting. The nucleus has
contracted also because of the extrusion of molten matter, the
loss of constituent gases given off in volcanic eruptions, and
(still more important) the compression and consolidation of its
material under gravity. As the nucleus contracts, it tends to draw
away from the cooled and solid crust, and the latter settles,
adapting itself to the shrinking nucleus much as the skin of a
withering apple wrinkles down upon the shrunken fruit. The
unsupported weight of the spherical crust develops enormous
tangential pressures, similar to the stresses of an arch or dome,
and when these lateral thrusts accumulate beyond the power of
resistance the solid rock is warped and folded and broken.

Since the planet attained its present mass it has thus been
lessening in volume. Notwithstanding local and relative upheavals
the earth's surface on the whole has drawn nearer and nearer to
the center. The portions of the lithosphere which have been
carried down the farthest have received the waters of the oceans,
while those portions which have been carried down the least have
emerged as continents.

Although it serves our convenience to refer the movements of the
crust to the sea level as datum plane, it is understood that this
level is by no means fixed. Changes in the ocean basins increase
or reduce their capacity and thus lower or raise the level of the
sea. But since these basins are connected, the effect of any
change upon the water level is so distributed that it is far less
noticeable than a corresponding change would be upon the land.





CHAPTER XIII

METAMORPHISM AND MINERAL VEINS


Under the action of internal agencies rocks of all kinds may be
rendered harder, more firmly cemented, and more crystalline. These
processes are known as METAMORPHISM, and the rocks affected,
whether originally sedimentary or igneous, are called METAMORPHIC
ROCKS. We may contrast with metamorphism the action of external
agencies in weathering, which render rocks less coherent by
dissolving their soluble parts and breaking down their crystalline
grains.

CONTACT METAMORPHISM. Rocks beneath a lava flow or in contact with
igneous intrusions are found to be metamorphosed to various
degrees by the heat of the cooling mass. The adjacent strata may
be changed only in color, hardness, and texture. Thus, next to a
dike, bituminous coal may be baked to coke or anthracite, and
chalk and limestone to crystalline marble. Sandstone may be
converted into quartzite, and shale into ARGILLITE, a compact,
massive clay rock. New minerals may also be developed. In
sedimentary rocks there may be produced crystals of mica and of
GARNET (a mineral as hard as quartz, commonly occurring in red,
twelve-sided crystals). Where the changes are most profound, rocks
may be wholly made over in structure and mineral composition.

In contact metamorphism, thin sheets of molten rock produce less
effect than thicker ones. The strongest heat effects are naturally
caused by bosses and regional intrusions, and the zone of change
about them may be several miles in width. In these changes heated
waters and vapors from the masses of igneous rocks undoubtedly
play a very important part.

Which will be more strongly altered, the rocks about a closed dike
in which lava began to cool as soon as it filled the fissure, or
the rocks about a dike which opened on the surface and through
which the molten rock flowed for some time?

Taking into consideration the part played by heated waters, which
will produce the most far-reaching metamorphism, dikes which cut
across the bedding planes or intrusive sheets which are thrust
between the strata?

REGIONAL METAMORPHISM. Metamorphic rocks occur wide-spread in many
regions, often hundreds of square miles in area, where such
extensive changes cannot be accounted for by igneous intrusions.
Such are the dissected cores of lofty mountains, as the Alps, and
the worn-down bases of ancient ranges, as in New England, large
areas in the Piedmont Belt, and the Laurentian peneplain.

In these regions the rocks have yielded to immense pressure. They
have been folded, crumpled, and mashed, and even their minute
grains, as one may see with a microscope, have often been
puckered, broken, and crushed to powder. It is to these mechanical
movements and strains which the rocks have suffered in every part
that we may attribute their metamorphism, and the degree to which
they have been changed is in direct proportion to the degree to
which they have been deformed and mashed.

Other factors, however, have played important parts. Rock crushing
develops heat, and allows a freer circulation of heated waters and
vapors. Thus chemical reactions are greatly quickened; minerals
are dissolved and redeposited in new positions, or their chemical
constituents may recombine in new minerals, entirely changing the
nature of the rock, as when, for example, feldspar recrystallizes
as quartz and mica.

Early stages of metamorphism are seen in SLATE. Pressure has
hardened the marine muds, the arkose, or the volcanic ash from
which slates are derived, and has caused them to cleave by the
rearrangement of their particles.

Under somewhat greater pressure, slate becomes PHYLLITE, a clay
slate whose cleavage surfaces are lustrous with flat-lying mica
flakes. The same pressure which has caused the rock to cleave has
set free some of its mineral constituents along the cleavage
planes to crystallize there as mica.

FOLIATION. Under still stronger pressure the whole structure of
the rock is altered. The minerals of which it is composed, and the
new minerals which develop by heat and pressure, arrange
themselves along planes of cleavage or of shear in rudely parallel
leaves, or FOLIA. Of this structure, called FOLIATION, we may
distinguish two types,--a coarser feldspathic type, and a fine
type in which other minerals than feldspar predominate.

GNEISS is the general name under which are comprised coarsely
foliated rocks banded with irregular layers of feldspar and other
minerals. The gneisses appear to be due in many cases to the
crushing and shearing of deep-seated igneous rocks, such as
granite and gabbro.

THE CRYSTALLINE SCHISTS, representing the finer types of
foliation, consist of thin, parallel, crystalline leaves, which
are often remarkably crumpled. These folia can be distinguished
from the laminae of sedimentary rocks by their lenticular form and
lack of continuity, and especially by the fact that they consist
of platy, crystalline grains, and not of particles rounded by
wear.

MICA SCHIST, the most common of schists, and in fact of all
metamorphic rocks, is composed of mica and quartz in alternating
wavy folia. All gradations between it and phyllite may be traced,
and in many cases we may prove it due to the metamorphism of
slates and shales. It is widespread in New England and along the
eastern side of the Appalachians. TALC SCHIST consists of quartz
and TALC, a light-colored magnesian mineral of greasy feel, and so
soft that it can be scratched with the thumb nail.

HORNBLENDE SCHIST, resulting in many cases from the foliation of
basic igneous rocks, is made of folia of hornblende alternating
with bands of quartz and feldspar. Hornblende schist is common
over large areas in the Lake Superior region.

QUARTZ SCHIST is produced from quartzite by the development of
fine folia of mica along planes of shear. All gradations may be
found between it and unfoliated quartzite on the one hand and mica
schist on the other.

Under the resistless pressure of crustal movements almost any
rocks, sandstones, shales, lavas of all kinds, granites, diorites,
and gabbros may be metamorphosed into schists by crushing and
shearing. Limestones, however, are metamorphosed by pressure into
marble, the grains of carbonate of lime recrystallizing freely to
interlocking crystals of calcite.

These few examples must suffice of the great class of metamorphic
rocks. As we have seen, they owe their origin to the alteration of
both of the other classes of rocks--the sedimentary and the
igneous--by heat and pressure, assisted usually by the presence of
water. The fact of change is seen in their hardness arid
cementation, their more or less complete recrystallization, and
their foliation; but the change is often so complete that no trace
of their original structure and mineral composition remains to
tell whether the rocks from which they were derived were
sedimentary or igneous, or to what variety of either of these
classes they belonged.

In many cases, however, the early history of a metamorphic rock
can be deciphered. Fossils not wholly obliterated may prove it
originally water-laid. Schists may contain rolled-out pebbles,
showing their derivation from a conglomerate. Dikes of igneous
rocks may be followed into a region where they have been foliated
by pressure. The most thoroughly metamorphosed rocks may sometimes
be traced out into unaltered sedimentary or igneous rocks, or
among them may be found patches of little change where their
history maybe read.

Metamorphism is most common among rocks of the earlier geological
ages, and most rare among rocks of recent formation. No doubt it
is now in progress where deep-buried sediments are invaded
by heat either from intrusive igneous masses or from the earth's
interior, or are suffering slow deformation under the thrust of
mountain-making forces.

Suggest how rocks now in process of metamorphism may sometimes be
exposed to view. Why do metamorphic rocks appear on the surface
to-day?

MINERAL VEINS

In regions of folded and broken rocks fissures are frequently
found to be filled with sheets of crystalline minerals deposited
from solution by underground water, and fissures thus filled are
known as mineral veins. Much of the importance of mineral veins is
due to the fact that they are often metalliferous, carrying
valuable native metals and metallic ores disseminated in fine
particles, in strings, and sometimes in large masses in the midst
of the valueless nonmetallic minerals which make up what is known
as the VEIN STONE.

The most common vein stones are QUARTZ and CALCITE. FLUORITE
(calcium fluoride), a mineral harder than calcite and
crystallizing in cubes of various colors, and BARITE (barium
sulphate), a heavy white mineral, are abundant in many veins.

The gold-bearing quartz veins of California traverse the
metamorphic slates of the Sierra Nevada Mountains. Below the zone
of solution (p. 45) these veins consist of a vein stone of quartz
mingled with pyrite (p. 13), the latter containing threads and
grains of native gold. But to the depth of about fifty feet from
the surface the pyrite of the vein has been dissolved, leaving a
rusty, cellular quartz with grains of the insoluble gold scattered
through it.

The PLACER DEPOSITS of California and other regions are gold-
bearing deposits of gravel and sand in river beds. The heavy gold
is apt to be found mostly near or upon the solid rock, and its
grains, like those of the sand, are always rounded. How the gold
came in the placers we may leave the pupil to suggest.

Copper is found in a number of ores, and also in the native metal.
Below the zone of surface changes the ore of a copper vein is
often a double sulphide of iron and copper called CHALCOPYRITE, a
mineral softer than pyrite--it can easily be scratched with a
knife--and deeper yellow in color. For several score of feet below
the ground the vein may consist of rusty quartz from which the
metallic ores have been dissolved; but at the base of the zone of
solution we may find exceedingly rich deposits of copper ores,--
copper sulphides, red and black copper oxides, and green and blue
copper carbonates, which have clearly been brought down in
solution from the leached upper portion of the vein.

ORIGIN OF MINERAL VEINS. Both vein stones and ores have been
deposited slowly from solution in water, much as crystals of salt
are deposited on the sides of a jar of saturated brine. In our
study of underground water we learned that it is everywhere
circulating through the permeable rocks of the crust, descending
to profound depths under the action of gravity and again driven to
the surface by hydrostatic pressure. Now fissures, wherever they
occur, form the trunk channels of the underground circulation.
Water descends from the surface along these rifts; it moves
laterally from either side to the fissure plane, just as ground
water seeps through the surrounding rocks from every direction to
a well; and it ascends through these natural water ways as in an
artesian well, whenever they intersect an aquifer in which water
is under hydrostatic pressure.

The waters which deposit vein stones and ores are commonly hot,
and in many cases they have derived their heat from intrusions of
igneous rock still uncooled within the crust. The solvent power of
the water is thus greatly increased, and it takes up into solution
various substances from the igneous and sedimentary rocks which it
traverses. For various reasons these substances stances are
deposited in the vein as ores and vein stones. On rising through
the fissure the water cools and loses pressure, and its capacity
to hold minerals in solution is therefore lessened. Besides, as
different currents meet in the fissure, some ascending, some
descending, and some coming in from the sides, the chemical
reaction of these various weak solutions upon one another and upon
the walls of the vein precipitates the minerals of vein stuffs and
ores.