John Lothrop Motley - "History of the United Netherlands, 1588"

A. H. Leahy - "Heroic Romances of Ireland Volume 2"

Mrs Charles (Ellen) Clacy - "A Lady's Visit to the Gold Diggings of Australia in 1852 53"

John Kendrick Bangs - "The Pursuit of the House Boat"

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

Looking for Child to be on Cover of a New Book, 'The Model Child'
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




1. Mountain ranges are made of belts of enormously and
exceptionally thick sediments. The strata of the Appalachians are
thirty thousand feet thick, while the same formations thin out to
five thousand feet in the Mississippi valley. The folds of the
Wasatch Mountains involve strata thirty thousand feet thick, which
thin to two thousand feet in the region of the Plains.

2. The sedimentary strata of which mountains are made are for the
most part the shallow-water deposits of continental deltas.
Mountain ranges have been upfolded along the margins of
continents.

3. Shallow-water deposits of the immense thickness found in
mountain ranges can be laid only in a gradually sinking area. A
profound subsidence, often to be reckoned in tens of thousands of
feet, precedes the upfolding of a mountain range.

Thus the history of mountains of folding is as follows: For long
ages the sea bottom off the coast of a continent slowly subsides,
and the great trough, as fast as it forms, is filled with
sediments, which at last come to be many thousands of feet thick.
The downward movement finally ceases. A slow but resistless
pressure sets in, and gradually, and with a long series of many
intermittent movements, the vast mass of accumulated sediments is
crumpled and uplifted into a mountain range.

FRACTURES AND DISLOCATIONS OF THE CRUST

Considering the immense stresses to which the rocks of the crust
are subjected, it is not surprising to find that they often yield
by fracture, like brittle bodies, instead of by folding and
flowing, like plastic solids. Whether rocks bend or break depends
on the character and condition of the rocks, the load of overlying
rocks which they bear, and the amount of the force and the
slowness with which it is applied.

JOINTS. At the surface, where their load is least, we find rocks
universally broken into blocks of greater or less size by partings
known as joints. Under this name are included many division planes
caused by cooling and drying; but it is now generally believed
that the larger and more regular joints, especially those which
run parallel to the dip and strike of the strata, are fractures
due to up-and-down movements and foldings and twistings of the
rocks.

Joints are used to great advantage in quarrying, and we have seen
how they are utilized by the weather in breaking up rock masses,
by rivers in widening their valleys, by the sea in driving back
its cliffs, by glaciers in plucking their beds, and how they are
enlarged in soluble rocks to form natural passageways for
underground waters. The ends of the parted strata match along both
sides of joint planes; in. joints there has been little or no
displacement of the broken rocks.

FAULTS. In Figure 184 the rocks have been both broken and
dislocated along the plane ff'. One side must have been moved up
or down past the other. Such a dislocation is called a fault. The
amount of the displacement, as measured by the vertical distance
between the ends of a parted layer, is the throw. The angle which
the fault plane makes with the vertical is the HADE. In Figure 184
the right side has gone down relatively to the left; the right is
the side of the downthrow, while the left is the side of the
upthrow. Where the fault plane is not vertical the surfaces on the
two sides may be distinguished as the HANGING WALL and the FOOT
WALL. Faults differ in throw from a fraction of an inch to many
thousands of feet.

SLICKENSIDES. If we examine the walls of a fault, we may find
further evidence of movement in the fact that the surfaces are
polished and grooved by the enormous friction which they have
suffered as they have ground one upon the other. These
appearances, called sliekensides, have sometimes been mistaken for
the results of glacial action.

NORMAL FAULTS. Faults are of two kinds,--normal faults and thrust
faults. Normal faults, of which Figure 184 is an example, hade to
the downthrow; the hanging wall has gone down. The total length of
the strata has been increased by the displacement. It seems that
the strata have been stretched and broken, and that the blocks
have readjusted themselves under the action of gravity as they
settled.

THRUST FAULTS. Thrust faults hade to the upthrow; the hanging wall
has gone up. Clearly such faults, where the strata occupy less
space than before, are due to lateral thrust. Folds and thrust
faults are closely associated. Under lateral pressure strata may
fold to a certain point and then tear apart and fault along the
surface of least resistance. Under immense pressure strata also
break by shear without folding. Thus, in Figure 185, the rigid
earth block under lateral thrust has found it easier to break
along the fault plane than to fold. Where such faults are nearly
horizontal they are distinguished as THRUST PLANES.

In all thrust faults one mass has been pushed over another, so as
to bring the underlying and older strata upon younger beds; and
when the fault planes are nearly horizontal, and especially when
the rocks have been broken into many slices which have slidden far
one upon another, the true succession of strata is extremely hard
to decipher.

In the Selkirk Mountains of Canada the basement rocks of the
region have been driven east for seven miles on a thrust plane,
over rocks which originally lay thousands of feet above them.

Along the western Appalachians, from Virginia to Georgia, the
mountain folds are broken by more than fifteen parallel thrust
planes, running from northeast to southwest, along which the older
strata have been pushed westward over the younger. The longest
continuous fault has been traced three hundred and seventy-five
miles, and the greatest horizontal displacement has been estimated
at not less than eleven miles.

CRUSH BRECCIA. Rocks often do not fault with a clean and simple
fracture, but along a zone, sometimes several yards in width, in
which they are broken to fragments. It may occur also that strata
which as a whole yield to lateral thrust by folding include beds
of brittle rocks, such as thin-layered limestones, which are
crushed to pieces by the strain. In either case the fragments when
recemented by percolating waters form a rock known as a CRUSH
BRECCIA (pronounced BRETCHA).

Breccia is a term applied to any rock formed of cemented ANGULAR
fragments. This rock may be made by the consolidation of volcanic
cinders, of angular waste at the foot of cliffs, or of fragments
of coral torn by the waves from coral reefs, as well as of strata
crushed by crustal movements.

SURFACE FEATURES DUE TO DISLOCATIONS

FAULT SCARPS. A fault of recent date may be marked at surface by a
scarp, because the face of the upthrown block has not yet been
worn to the level of the downthrow side.

After the upthrown block has been worn down to this level,
differential erosion produces fault scarps wherever weak rocks and
resistant rocks are brought in contact along the fault plane; and
the harder rocks, whether on the upthrow or the downthrow side,
emerge in a line of cliffs. Where a fault is so old that no abrupt
scarps appear, its general course is sometimes marked by the line
of division between highland and lowland or hill and plain. Great
faults have sometimes brought ancient crystalline rocks in contact
with weaker and younger sedimentary rocks, and long after erosion
has destroyed all fault scarps the harder crystallines rise in an
upland of rugged or mountainous country which meets the lowland
along the line of faulting.

The vast majority of faults give rise to no surface features. The
faulted region may be old enough to have been baseleveled, or the
rocks on both sides of the line of dislocation may be alike in
their resistance to erosion and therefore have been worn down to a
common slope. The fault may be entirely concealed by the mantle of
waste, and in such cases it can be inferred from abrupt changes in
the character or the strike and dip of the strata where they may
outcrop near it.

The plateau trenched by the Grand Canyon of the Colorado River
exhibits a series of magnificent fault scarps whose general course
is from north to south, marking the edges of the great crust
blocks into which the country has been broken. The highest part of
the plateau is a crust block ninety miles long and thirty-five
miles in maximum width, which has been hoisted to nine thousand
three hundred feet above, sea level. On the east it descends four
thousand feet by a monoclinal fold, which passes into a fault
towards the north. On the west it breaks down by a succession of
terraces faced by fault scarps. The throw of these faults varies
from seven hundred feet to more than a mile. The escarpments,
however, are due in a large degree to the erosion of weaker rock
on the downthrow side.

The Highlands of Scotland meet the Lowlands on the south with a
bold front of rugged hills along a line of dislocation which runs
across the country from sea to sea. On the one side are hills of
ancient crystalline rocks whose crumpled structures prove that
they are but the roots of once lofty mountains; on the other lies
a lowland of sandstone and other stratified rocks formed from the
waste of those long-vanished mountain ranges. Remnants of
sandstone occur in places on the north of the great fault, and are
here seen to rest on the worn and fairly even surface of the
crystallines. We may infer that these ancient mountains were
reduced along their margins to low plains, which were slowly
lowered beneath the sea to receive a cover of sedimentary rocks.
Still later came an uplift and dislocation. On the one side
erosion has since stripped off the sandstones for the most part,
but the hard crystalline rocks yet stand in bold relief. On the
other side the weak sedimentary rocks have been worn down to
lowlands.

RIFT VALLEYS. In a broken region undergoing uplift or the unequal
settling which may follow, a slice inclosed between two fissures
may sink below the level of the crust blocks on either side, thus
forming a linear depression known as a rift valley, or valley of
fracture.

One of the most striking examples of this rare type of valley is
the long trough which runs straight from the Lebanon Mountains of
Syria on the north to the Red Sea on the south, and whose central
portion is occupied by the Jordan valley and the Dead Sea. The
plateau which it gashes has been lifted more than three thousand
feet above sea level, and the bottom of the trough reaches a depth
of two thousand six hundred feet below that level in parts of the
Dead Sea. South of the Dead Sea the floor of the trough rises
somewhat above sea level, and in the Gulf of Akabah again sinks
below it. This uneven floor could be accounted for either by the
profound warping of a valley of erosion or by the unequal
depression of the floor of a rift valley. But that the trough is a
true valley of fracture is proved by the fact that on either side
it is bounded by fault scarps and monoclinal folds. The keystone
of the arch has subsided. Many geologists believe that the Jordan-
Akabah trough, the long narrow basin of the Red Sea, and the chain
of down-faulted valleys which in Africa extends from the strait of
Bab-el-Mandeb as far south as Lake Nyassa--valleys which contain
more than thirty lakes--belong to a single system of dislocation.

Should you expect the lateral valleys of a rift valley at the time
of its formation to enter it as hanging valleys or at a common
level?

BLOCK MOUNTAINS. Dislocations take place on so grand a scale that
by the upheaval of blocks of the earth's crust or the down-
faulting of the blocks about one which is relatively stationary,
mountains known as block mountains are produced. A tilted crust
block may present a steep slope on the side upheaved and a more
gentle descent on the side depressed.

THE BASIN RANGES. The plateaus of the United States bounded by the
Rocky Mouirtains on the east, and on the west by the ranges which
front the Pacific, have been profoundly fractured and faulted. The
system of great fissures by which they are broken extends north
and south, and the long, narrow, tilted crust blocks intercepted
between the fissures give rise to the numerous north-south ranges
of the region. Some of the tilted blocks, as those of southern
Oregon, are as yet but moderately carved by erosion, and shallow
lakes lie on the waste that has been washed into the depressions
between them. We may therefore conclude that their displacement is
somewhat recent. Others, as those of Nevada, are so old that they
have been deeply dissected; their original form has been destroyed
by erosion, and the intermontane depressions are occupied by wide
plains of waste.

DISLOCATIONS AND RIVER VALLEYS. Before geologists had proved that
rivers can by their own unaided efforts cut deep canyons, it was
common to consider any narrow gorge as a gaping fissure of the
crust. This crude view has long since been set aside. A map of the
plateaus of northern Arizona shows how independent of the immense
faults of the region is the course of the Colorado River. In the
Alps the tunnels on the Saint Gotthard railway pass six times
beneath the gorge of the Reuss, but at no point do the rocks show
the slightest trace of a fault.

RATE OF DISLOCATION. So far as human experience goes, the earth
movements which we have just studied, some of which have produced
deep-sunk valleys and lofty mountain ranges, and faults whose
throw is to be measured in thousands of feet, are slow and
gradual. They are not accomplished by a single paroxysmal effort,
but by slow creep and a series of slight slips continued for vast
lengths of time.

In the Aspen mining district in Colorado faulting is now going on
at a comparatively rapid rate. Although no sudden slips take
place, the creep of the rock along certain planes of faulting
gradually bends out of shape the square-set timbers in horizontal
drifts and has closed some vertical shafts by shifting the upper
portion across the lower. Along one of the faults of this region
it is estimated that there has been a movement of at least four
hundred feet since the Glacial epoch. More conspicuous are the
instances of active faulting by means of sudden slips. In 1891
there occurred along an old fault plane in Japan a slip which
produced an earth rent traced for fifty miles (Fig. 192). The
country on one side was depressed in places twenty feet below that
on the other, and also shifted as much as thirteen feet
horizontally in the direction of the fault line.

In 1872 a slip occurred for forty miles on the great line of
dislocation which runs along the eastern base of the Sierra Nevada
Mountains. In the Owens valley, California, the throw amounted to
twenty-five feet in places, with a horizontal movement along the
fault line of as much as eighteen feet. Both this slip and that in
Japan just mentioned caused severe earthquakes.

For the sake of clearness we have described oscillations,
foldings, and fractures of the crust as separate processes, each
giving rise to its own peculiar surface features, but in nature
earth movements are by no means so simple,--they are often
implicated with one another: folds pass into faults; in a deformed
region certain rocks have bent, while others under the same
strain, but under different conditions of plasticity and load,
have broken; folded mountains have been worn to their roots, and
the peneplains to which they have been denuded have been upwarped
to mountain height and afterwards dissected,--as in the case of
the Alleghany ridges, the southern Carpathians, and other ranges,
--or, as in the case of the Sierra Nevada Mountains, have been
broken and uplifted as mountains of fracture.

Draw the following diagrams, being careful to show the direction
in which the faulted blocks have moved, by the position of the two
parts of some well-defined layer of limestone, sandstone, or
shale, which occurs on each side of the fault plane, as in Figure
184.

1. A normal fault with a hade of 15 degrees, the original fault
scarp remaining.

2. A normal fault with a hade of 50 degrees, the original fault
scarp worn away, showing cliffs caused by harder strata on the
downthrow side.

3. A thrust fault with a hade of 30 degrees, showing cliffs due to
harder strata outcropping on the downthrow.

4. A thrust fault with a hade of 80 degrees, with surface
baseleveled.

5. In a region of normal faults a coal mine is being worked along
the seam of coal AB (Fig. 193). At B it is found broken by a fault
f which hades toward A. To find the seam again, should you advise
tunneling up or down from B?

6. In a vertical shaft of a coal mine the same bed of coal is
pierced twice at different levels because of a fault. Draw a
diagram to show whether the fault is normal or a thrust.

7. Copy the diagram in Figure 194, showing how the two ridges may
be accounted for by a single resistant stratum dislocated by a
fault. Is the fault a STRIKE FAULT, i.e. one running parallel with
the strike of the strata, or a DIP FAULT, one running parallel
with the direction of the dip?

8. Draw a diagram of the block in Figure 195 as it would appear if
dislocated along the plane efg by a normal fault whose throw
equals one fourth the height of the block. Is the fault a strike
or a dip fault? Draw a second diagram showing the same block after
denudation has worn it down below the center of the upthrown side.
Note that the outcrop of the coal seam is now deceptively
repeated. This exercise may be done in blocks of wood instead of
drawings.

9. Draw diagrams showing by dotted lines the conditions both of A
and of B, Figure 196, after deformation had given the strata their
present attitude.

10. What is the attitude of the strata of this earth block, Figure
197? What has taken place along the plane bef? When did the
dislocation occur compared with the folding of the strata? With
the erosion of the valleys on the right-hand side of the mountain?
With the deposition of the sediments? Do you find any remnants of
the original surface baf produced by the dislocation? From the
left-hand side of the mountain infer what was the relief of the
region before the dislocation. Give the complete history recorded
in the diagram from the deposition of the strata to the present.

11. Which is the older fault, in Figure 198, or When did the lava
flow occur? How long a time elapsed between the formation of the
two faults as measured in the work done in the interval? How long
a time since the formation of the later fault?

12. Measure by the scale the thickness lie of the coal-bearing
strata outcropping from a to b in Figure 199. On any convenient
scale draw a similar section of strata with a dip of 30 degrees
outcropping along a horizontal line normal to the strike one
thousand feet in length, and measure the thickness of the strata
by the scale employed. The thickness may also be calculated by
trigonometry.

UNCONFORMITY

Strata deposited one upon, another in an unbroken succession are
said to be conformable. But the continuous deposition of strata is
often interrupted by movements of the earth's crust, Old sea
floors are lifted to form land and are again depressed beneath the
sea to receive a cover of sediments only after an interval during
which they were carved by subaerial erosion. An erosion surface
which thus parts older from younger strata is known as an
UNCONFORMITY, and the strata above it are said to be UNCONFORMABLE
with the rocks below, or to rest unconformably upon them. An
unconformity thus records movements of the crust and a consequent
break in the deposition of the strata. It denotes a period of land
erosion of greater or less length, which may sometimes be roughly
measured by the stage in the erosion cycle which the land surface
had attained before its burial. Unconformable strata may be
parallel, as in Figure 200, where the record includes the
deposition of strata, their emergence, the erosion of the land
surface, a submergence and the deposit of the strata, and lastly,
emergence and the erosion of the present surface.

Often the earth movements to which the uplift or depression was
due involved tilting or folding of the earlier strata, so that the
strata are now nonparallel as well as unconformable. In Figure
201, for example, the record includes deposition, uplift, and
tilting of a; erosion, depression, the deposit of b; and finally
the uplift which has brought the rocks to open air and permitted
the dissection by which the unconformity is revealed. From this
section infer that during early Silurian times the area was sea,
and thick sea muds were laid upon it. These were later altered to
hard slates by pressure and upfolded into mountains. During the
later Silurian and the Devonian the area was land and suffered
vast denudation. In the Carboniferous period it was lowered
beneath the sea and received a cover of limestone.

THE AGE OF MOUNTAINS. It is largely by means of unconformities
that we read the history of mountain making and other deformations
and movements of the crust. In Figure 203, for example, the
deformation which upfolded the range of mountains took place after
the deposit of the series of strata a of which the mountains are
composed, and before the deposit of the stratified rocks, which
rest unconformably on a and have not shared their uplift.

Most great mountain ranges, like the Sierra Nevada and the Alps,
mark lines of weakness along which the earth's crust has yielded
again and again during the long ages of geological time. The
strata deposited at various times about their flanks have been
infolded by later crumplings with the original mountain mass, and
have been repeatedly crushed, inverted, faulted, intruded with
igneous rocks, and denuded. The structure of great mountain ranges
thus becomes exceedingly complex and difficult to read. A
comparatively simple case of repeated uplift is shown in Figure
204. In the section of a portion of the Alps shown in Figure 179 a
far more complicated history may be deciphered.

UNCONFORMITIES IN THE COLORADO CANYON, ARIZONA. How geological
history may be read in unconformities is further illustrated in
Figures 207 and 208. The dark crystalline rocks a at the bottom of
the canyon are among the most ancient known, and are overlain
unconformably by a mass of tilted coarse marine sandstones b,
whose total thickness is not seen in the diagram and measures
twelve thousand feet perpendicularly to the dip. Both a and b rise
to a common level nn and upon them rest the horizontal sea-laid
strata c, in which the upper portion of the canyon has been cut.

Note that the crystalline rocks a have been crumpled and crushed.
Comparing their structure with that of folded mountains, what do
you infer as to their relief after their deformation? To which
surface were they first worn down, mm' or nm? Describe and account
for the surface mm'. How does it differ from the surface of the
crystalline rocks seen in the Torridonian Mountains, and why? This
surface mm' is one of the oldest land surfaces of which any
vestige remains.

It is a bit of fossil geography buried from view since the
earliest geological ages and recently brought to light by the
erosion of the canyon.

How did the surface mm' come to receive its cover of sandstones b?
From the thickness and coarseness of these sediments draw
inferences as to the land mass from which they were derived. Was
it rising or subsiding? high or low? Were its streams slow or
swift? Was the amount of erosion small or great?

Note the strong dip of these sandstones b. Was the surface mm'
tilted as now when the sandstones were deposited upon it? When was
it tilted? Draw a diagram showing the attitude of the rocks after
this tilting occurred, and their height relative to sea level.

The surface nn' is remarkably even, although diversified by some
low hills which rise into the bedded rocks of c, and it may be
traced for long distances up and down the canyon. Were the layers
of b and the surface mm' always thus cut short by nn' as now? What
has made the surface nn' so even? How does it come to cross the
hard crystalline rocks a and the weaker sandstones b at the same
impartial level? How did the sediments of c come to be laid upon
it? Give now the entire history recorded in the section, and in
addition that involved in the production of the platform P, shown
in Figure 130, and that of the cutting of the canyon. How does the
time involved in the cutting of the canyon compare with that
required for the production of the surfaces mm', nn', and P?





CHAPTER X

EARTHQUAKES


Any sudden movement of the rocks of the crust, as when they tear
apart when a fissure is formed or extended, or slip from time to
time along a growing fault, produces a jar called an earthquake,
which spreads in all directions from the place of disturbance.

THE CHARLESTON EARTHQUAKE. On the evening of August 31, 1886, the
city of Charleston, S.C., was shaken by one of the greatest
earthquakes which has occurred in the United States. A slight
tremor which rattled the windows was followed a few seconds later
by a roar, as of subterranean thunder, as the main shock passed
beneath the city. Houses swayed to and fro, and their heaving
floors overturned furniture and threw persons off their feet as,
dizzy and nauseated, they rushed to the doors for safety. In sixty
seconds a number of houses were completely wrecked, fourteen
thousand chimneys were toppled over, and in all the city scarcely
a building was left without serious injury. In the vicinity of
Charleston railways were twisted and trains derailed. Fissures
opened in the loose superficial deposits, and in places spouted
water mingled with sand from shallow underlying aquifers.