Amelia Edith Barr - "The Hallam Succession"

Pierre Loti - "Madame Chrysantheme, v3"

Christopher Morley - "Kathleen"

J. Cuthbert Hadden - "Haydn"

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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.

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Books: The Elements of Geology

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




STRATIFICATION. For the most part the sheet of sea-laid waste is
hidden from our sight. Where its edge is exposed along the shore
we may see the surface markings which have just been noticed.
Soundings also, and the observations made in shallow waters by
divers, tell something of its surface; but to learn more of its
structures we must study those ancient sediments which have been
lifted from the sea and dissected by subaerial agencies. From them
we ascertain that sea deposits are stratified. They lie in
distinct layers which often differ from one another in thickness,
in size of particles, and perhaps in color. They are parted by
bedding planes, each of which represents either a change in
material or a pause during which deposition ceased and the
material of one layer had time to settle and become somewhat
consolidated before the material of the next was laid upon
it. Stratification is thus due to intermittently acting forces,
such as the agitation of the water during storms, the flow and ebb
of the tide, and the shifting channels of tidal currents. Off the
mouths of rivers, stratification is also caused by the coarser and
more abundant material brought down at time of floods being laid
on the finer silt which is discharged during ordinary stages.

How stratified deposits are built up is well illustrated in the
flats which border estuaries, such as the Bay of Fundy. Each
advance of the tide spreads a film of mud, which dries and hardens
in the air during low water before another film is laid upon it by
the next incoming tidal flood. In this way the flats have been
covered by a clay which splits into leaves as thin as sheets of
paper.

It is in fine material, such as clays and shales and limestones,
that the thinnest and most uniform layers, as well as those of
widest extent, occur. On the other hand, coarse materials are
commonly laid in thick beds, which soon thin out seaward and give
place to deposits of finer stuff. In a general way strata are laid
in well-nigh horizontal sheets, for the surface on which they are
laid is generally of very gentle inclination. Each stratum,
however, is lenticular, or lenslike, in form, having an area where
it is thickest, and thinning out thence to its edges, where it is
overlapped by strata similar in shape.

CROSS BEDDING. There is an apparent exception to this rule where
strata whose upper and lower surfaces may be about horizontal are
made up of layers inclined at angles which may be as high as the
angle of repose. In this case each stratum grew by the addition
along its edge of successive layers of sediment, precisely as does
a sand bar in a river, the sand being pushed continuously over the
edge and coming to rest on a sloping surface. Shoals built by
strong and shifting tidal currents often show successive strata in
which the cross bedding is inclined in different directions.

THICKNESS OF SEA DEPOSITS. Remembering the vast amount of
material denuded from the land and deposited offshore, we should
expect that with the lapse of time sea deposits would have grown
to an enormous thickness. It is a suggestive fact that, as a rule,
the profile of the ocean bed is that of a soup plate,--a basin
surrounded by a flaring rim. On the CONTINENTAL SHELF, as the rim
is called, the water is seldom more than six hundred feet in depth
at the outer edge, and shallows gradually towards shore. Along the
eastern coast of the United States the continental shelf is from
fifty to one hundred and more miles in width; on the Pacific coast
it is much narrower. So far as it is due to upbuilding, a wide
continental shelf, such as that of the Atlantic coast, implies a
massive continental delta thousands of feet in thickness. The
coastal plain of the Atlantic states may be regarded as the
emerged inner margin of this shelf, and borings made along the
coast probe it to the depth of as much as three thousand feet
without finding the bottom of ancient offshore deposits.
Continental shelves may also be due in part to a submergence of
the outer margin of a continental plateau and to marine abrasion.

DEPOSITION OF SEDIMENTS AND SUBSIDENCE. The stratified rocks of
the land show in many places ancient sediments which reach a
thickness which is measured in miles, and which are yet the
product of well-nigh continuous deposition. Such strata may prove
by their fossils and by their composition and structure that they
were all laid offshore in shallow water. We must infer that,
during the vast length of time recorded by the enormous pile, the
floor of the sea along the coast was slowly sinking, and that the
trough was constantly being filled, foot by foot, as fast as it
was depressed. Such gradual, quiet movements of the earth's crust
not only modify the outline of coasts, as we have seen, but are of
far greater geological importance in that they permit the making
of immense deposits of stratified rock.

A slow subsidence continued during long time is recorded also in
the succession of the various kinds of rock that come to be
deposited in the same area. As the sea transgresses the land, i.e.
encroaches upon it, any given part of the sea bottom is brought
farther and farther from the shore. The basal conglomerate formed
by bowlder and pebble beaches comes to be covered with sheets of
sand, and these with layers of mud as the sea becomes deeper and
the shore more remote; while deposits of limestone are made when
at last no waste is brought to the place from the now distant
land, and the water is left clear for the growth of mollusks and
other lime-secreting organisms.

RATE OF DEPOSITION. As deposition in the sea corresponds to
denudation on the land, we are able to make a general estimate of
the rate at which the former process is going on. Leaving out of
account the soluble matter removed, the Mississippi is lowering
its basin at the rate of one foot in five thousand years, and we
may assume this as the average rate at which the earth's land
surface of fifty-seven million square miles is now being denuded
by the removal of its mechanical waste. But sediments from the
land are spread within a zone but two or three hundred miles in
width along the margin of the continents, a line one hundred
thousand miles long. As the area of deposition--about twenty-five
million square miles--is about one half the area of denudation,
the average rate of deposition must be twice the average rate of
denudation, i.e. about one foot in twenty-five hundred years. If
some deposits are made much more rapidly than this, others are
made much more slowly. If they were laid no faster than the
present average rate, the strata of ancient sea deposits exposed
in a quarry fifty feet deep represent a lapse of at least one
hundred and twenty-five thousand years, and those of a formation
five hundred feet thick required for their accumulation one
million two hundred and fifty thousand years.

THE SEDIMENTARY RECORD AND THE DENUDATION CYCLE. We have seen that
the successive stages in a cycle of denudation, such as that by
which a land mass of lofty mountains is worn to low plains, are
marked each by its own peculiar land forms, and that the forms of
the earlier stages are more or less completely effaced as the
cycle draws toward an end. Far more lasting records of each stage
are left in the sedimentary deposits of the continental delta.

Thus, in the youth of such a land mass as we have mentioned,
torrential streams flowing down the steep mountain sides deliver
to the adjacent sea their heavy loads of coarse waste, and thick
offshore deposits of sand and gravel (Fig. 156) record the high
elevation of the bordering land. As the land is worn to lower
levels, the amount and coarseness of the waste brought to the sea
diminishes, until the sluggish streams carry only a fine silt
which settles on the ocean floor near to land in wide sheets of
mud which harden into shale. At last, in the old age of the region
(Fig. 157), its low plains contribute little to the sea except the
soluble elements of the rocks, and in the clear waters near the
land lime-secreting organisms flourish and their remains
accumulate in beds of limestone. When long-weathered lands
mantled with deep, well-oxidized waste are uplifted by a gradual
movement of the earth's crust, and the mantle is rapidly stripped
off by the revived streams, the uprise is recorded in wide
deposits of red and yellow clays and sands upon the adjacent ocean
floor.

Where the waste brought in is more than the waves can easily
distribute, as off the mouths of turbid rivers which drain
highlands near the sea, deposits are little winnowed, and are laid
in rapidly alternating, shaly sandstones and sandy shales.

Where the highlands are of igneous rock, such as granite, and
mechanical disintegration is going on more rapidly than chemical
decay, these conditions are recorded in the nature of the deposits
laid offshore. The waste swept in by streams contains much
feldspar and other minerals softer and more soluble than quartz,
and where the waves have little opportunity to wear and winnow it,
it comes to rest in beds of sandstone in which grains of feldspar
and other soft minerals are abundant. Such feldspathic sandstones
are known as ARKOSE.

On the other hand, where the waste supplied to the sea comes
chiefly from wide, sandy, coastal plains, there are deposited off-
shore clean sandstones of well-worn grains of quartz alone. In
such coastal plains the waste of the land is stored for ages.
Again and again they are abandoned and invaded by the sea as from
time to time the land slowly emerges and is again submerged. Their
deposits are long exposed to the weather, and sorted over by the
streams, and winnowed and worked over again and again by the
waves. In the course of long ages such deposits thus become
thoroughly sorted, and the grains of all minerals softer than
quartz are ground to mud.

DEEP-SEA OOZES AND CLAYS

GLOBIGERINA OOZE. Beyond the reach of waste from the land the
bottom of the deep sea is carpeted for the most part with either
chalky ooze or a fine red clay. The surface waters of the warm
seas swarm with minute and lowly animals belonging to the order of
the Foraminifera, which secrete shells of carbonate of lime. At
death these tiny white shells fall through the sea water like
snowflakes in the air, and, slowly dissolving, seem to melt quite
away before they can reach depths greater than about three miles.
Near shore they reach bottom, but are masked by the rapid deposit
of waste derived from the land. At intermediate depths they mantle
the ocean floor with a white, soft lime deposit known as
Globigerina ooze, from a genus of the Foraminifera which
contributes largely to its formation.

RED CLAY. Below depths of from fifteen to eighteen thousand feet
the ocean bottom is sheeted with red or chocolate colored clay. It
is the insoluble residue of seashells, of the debris of submarine
volcanic eruptions, of volcanic dust wafted by the winds, and of
pieces of pumice drifted by ocean currents far from the volcanoes
from which they were hurled. The red clay builds up with such
inconceivable slowness that the teeth of sharks and the hard ear
bones of whales may be dredged in large numbers from the deep
ocean bed, where they have lain unburied for thousands of years;
and an appreciable part of the clay is also formed by the dust of
meteorites consumed in the atmosphere,--a dust which falls
everywhere on sea and land, but which elsewhere is wholly masked
by other deposits.

The dark, cold abysses of the ocean are far less affected by
change than any other portion of the surface of the lithosphere.
These vast, silent plains of ooze lie far below the reach of
storms. They know no succession of summer and winter, or of night
and day. A mantle of deep and quiet water protects them from the
agents of erosion which continually attack, furrow, and destroy
the surface of the land. While the land is the area of erosion,
the sea is the area of deposition. The sheets of sediment which
are slowly spread there tend to efface any inequalities, and to
form a smooth and featureless subaqueous plain.

With few exceptions, the stratified rocks of the land are proved
by their fossils and composition to have been laid in the sea; but
in the same way they are proved to be offshore, shallow-water
deposits, akin to those now making on continental shelves. Deep-
sea deposits are absent from the rocks of the land, and we may
therefore infer that the deep sea has never held sway where the
continents now are,--that the continents have ever been, as now,
the elevated portions of the lithosphere, and that the deep seas
of the present have ever been its most depressed portions.

THE REEF-BUILDING CORALS

In warm seas the most conspicuous of rock-making organisms are the
corals known as the reef builders. Floating in a boat over a coral
reef, as, for example, off the south coast of Florida or among the
Bahamas, one looks down through clear water on thickets of
branching coral shrubs perhaps as much as eight feet high, and
hemispherical masses three or four feet thick, all abloom with
countless minute flowerlike coral polyps, gorgeous in their colors
of yellow, orange, green, and red. In structure each tiny polyp is
little more than a fleshy sac whose mouth is surrounded with
petal-like tentacles, or feelers. From the sea water the polyps
secrete calcium carbonate and build it up into the stony framework
which supports their colonies. Boring mollusks, worms, and sponges
perforate and honeycomb this framework even while its surface is
covered with myriads of living polyps. It is thus easily broken by
the waves, and white fragments of coral trees strew the ground
beneath. Brilliantly colored fishes live in these coral groves,
and countless mollusks, sea urchins, and other forms of marine
life make here their home. With the debris from all these sources
the reef is constantly built up until it rises to low-tide level.
Higher than this the corals cannot grow, since they are killed by
a few hours' exposure to the air.

When the reef has risen to wave base, the waves abrade it on the
windward side and pile to leeward coral blocks torn from their
foundation, filling the interstices with finer fragments. Thus
they heap up along the reef low, narrow islands (Fig. 160).

Reef building is a comparatively rapid progress. It has been
estimated that off Florida a reef could be built up to the surface
from a depth of fifty feet in about fifteen hundred years.

CORAL LIMESTONES. Limestones of various kinds are due to the reef
builders. The reef rock is made of corals in place and broken
fragments of all sizes, cemented together with calcium carbonate
from solution by infiltrating waters. On the island beaches coral
sand is forming oolitic limestone, and the white coral mud with
which the sea is milky for miles about the reef in times of storm
settles and concretes into a compact limestone of finest grain.
Corals have been among the most important limestone builders of
the sea ever since they made their appearance in the early
geological ages.

The areas on which coral limestone is now forming are large. The
Great Barrier Reef of Australia, which lies off the north-eastern
coast, is twelve hundred and fifty miles long, and has a width of
from ten to ninety miles. Most of the islands of the tropics are
either skirted with coral reefs or are themselves of coral
formation.

CONDITIONS OF CORAL GROWTH. Reef-building corals cannot live
except in clear salt water less, as a rule, than one hundred and
fifty feet in depth, with a winter temperature not lower than 68
degrees F. An important condition also is an abundant food supply,
and this is best secured in the path of the warm oceanic currents.

Coral reefs may be grouped in three classes,--fringing reefs,
barrier reefs, and atolls.

FRINGING REEFS. These take their name from the fact that they are
attached as narrow fringes to the shore. An example is the reef
which forms a selvage about a mile wide along the northeastern
coast of Cuba. The outer margin, indicated by the line of white
surf, where the corals are in vigorous growth, rises from about
forty feet of water. Between this and the shore lies a stretch of
shoal across which one can wade at low water, composed of coral
sand with here and there a clump of growing coral.

BARRIER REEFS. Reefs separated from the shore by a ship channel of
quiet water, often several miles in width and sometimes as much as
three hundred feet in depth, are known as barrier reefs. The
seaward face rises abruptly from water too deep for coral growth.
Low islands are cast up by the waves upon the reef, and inlets
give place for the ebb and flow of the tides. Along the west coast
of the island of New Caledonia a barrier reef extends for four
hundred miles, and for a length of many leagues seldom approaches
within eight miles of the shore.

ATOLLS. These are ring-shaped or irregular coral islands, or
island-studded reefs, inclosing a central lagoon. The narrow zone
of land, like the rim of a great bowl sunken to the water's edge,
rises hardly more than twenty feet at most above the sea, and is
covered with a forest of trees such as the cocoanut, whose seeds
can be drifted to it uninjured from long distances. The white
beach of coral sand leads down to the growing reef, on whose outer
margin the surf is constantly breaking. The sea face of the reef
falls off abruptly, often to depths of thousands of feet, while
the lagoon varies in depth from a few feet to one hundred and
fifty or two hundred, and exceptionally measures as much as three
hundred and fifty feet.

THEORIES OF CORAL REEFS. Fringing reefs require no explanation,
since the depth of water about them is not greater than that at
which coral can grow; but barrier reefs and atolls, which may rise
from depths too great for coral growth demand a theory of their
origin.

Darwin's theory holds that barrier reefs and atolls are formed
from fringing reefs by SUBSIDENCE. The rate of sinking cannot be
greater than that of the upbuilding of the reef, since otherwise
the corals would be carried below their depth and drowned. The
process is illustrated in Figure 161, where v represents a
volcanic island in mid ocean undergoing slow depression, and ss
the sea level before the sinking began, when the island was
surrounded by a fringing reef. As the island slowly sinks, the
reef builds up with equal pace. It rears its seaward face more
steep than the island slope, and thus the intervening space
between the sinking, narrowing land and the outer margin of the
reef constantly widens. In this intervening space the corals are
more or less smothered with silt from the outer reef and from the
land, and are also deprived in large measure of the needful supply
of food and oxygen by the vigorous growth of the corals on the
outer rim. The outer rim thus becomes a barrier reef and the inner
belt of retarded growth is deepened by subsidence to a ship
channel, s's' representing sea level at this time. The final
stage, where the island has been carried completely beneath the
sea and overgrown by the contracting reef, whose outer ring now
forms an atoll, is represented by s"s".

In very many instances, however, atolls and barrier reefs may be
explained without subsidence. Thus a barrier reef may be formed by
the seaward growth of a fringing reef upon the talus of its sea
face. In Figure 162 f is a fringing reef whose outer wall rises
from about one hundred and fifty feet, the lower limit of the
reef-building species. At the foot of this submarine cliff a talus
of fallen blocks t accumulates, and as it reaches the zone of
coral growth becomes the foundation on which the reef is steadily
extended seaward. As the reef widens, the polyps of the
circumference flourish, while those of the inner belt are retarded
in their growth and at last perish. The coral rock of the inner
belt is now dissolved by sea water and scoured out by tidal
currents until it gives place to a gradually deepening ship
channel, while the outer margin is left as a barrier reef.

In much the same way atolls may be built on any shoal which lies
within the zone of coral growth. Such shoals may be produced when
volcanic islands are leveled by waves and ocean currents, and when
submarine plateaus, ridges, and peaks are built up by various
organic agencies, such as molluscous and foraminiferal shell
deposits. The reef-building corals, whose eggs are drifted widely
over the tropic seas by ocean currents, colonize such submarine
foundations wherever the conditions are favorable for their
growth. As the reef approaches the surface the corals of the inner
area are smothered by silt and starved, and their Submarine
Volcanic Peak hard parts are dissolved and scoured away; while
those of the circumference, with abundant food supply, nourish and
build the ring of the atoll. Atolls may be produced also by the
backward drift of sand from either end of a crescentic coral reef
or island, the spits uniting in the quiet water of the lee to
inclose a lagoon. In the Maldive Archipelago all gradations
between crescent-shaped islets and complete atoll rings have been
observed.

In a number of instances where coral reefs have been raised by
movements of the earth's crust, the reef formation is found to be
a thin veneer built upon a foundation of other deposits. Thus
Christmas Island, in the Indian Ocean, is a volcanic pile rising
eleven hundred feet above sea level and fifteen thousand five
hundred feet above the bottom of the sea. The summit is a plateau
surrounded by a rim of hills of reef formation, which represent
the ring of islets of an ancient atoll. Beneath the reef are thick
beds of limestone, composed largely of the remains of
foraminifers, which cover the lavas and fragraental materials of
the old submarine volcano.

Among the ancient sediments which now form the stratified rocks of
the land there occur many thin reef deposits, but none are known
of the immense thickness which modern reefs are supposed to reach
according to the theory of subsidence.

Barrier and fringing reefs are commonly interrupted off the mouths
of rivers. Why?

SUMMARY. We have seen that the ocean bed is the goal to which the
waste of the rocks of the land at last arrives. Their soluble
parts, dissolved by underground waters and carried to the sea by
rivers, are largely built up by living creatures into vast sheets
of limestone. The less soluble portions--the waste brought in by
streams and the waste of the shore--form the muds and sands of
continental deltas. All of these sea deposits consolidate and
harden, and the coherent rocks of the land are thus reconstructed
on the ocean floor. But the destination is not a final one. The
stratified rocks of the land are for the most part ancient
deposits of the sea, which have been lifted above sea level; and
we may believe that the sediments now being laid offshore are the
"dust of continents to be," and will some time emerge to form
additions to the land. We are now to study the movements of the
earth's crust which restore the sediments of the sea to the light
of day, and to whose beneficence we owe the habitable lands of the
present.





PART II

INTERNAL GEOLOGICAL AGENCIES

CHAPTER IX

MOVEMENTS OF THE EARTH'S CRUST


The geological agencies which we have so far studied--weathering,
streams, underground waters, glaciers, winds, and the ocean--all
work upon the earth from without, and all are set in motion by an
energy external to the earth, namely, the radiant energy of the
sun. All, too, have a common tendency to reduce the inequalities
of the earth's surface by leveling the lands and strewing their
waste beneath the sea.

But despite the unceasing efforts of these external agencies, they
have not destroyed the continents, which still rear their broad
plains and great plateaus and mountain ranges above the sea.
Either, then, the earth is very young and the agents of denudation
have not yet had time to do their work, or they have been opposed
successfully by other forces.

We enter now upon a department of our science which treats of
forces which work upon the earth from within, and increase the
inequalities of its surface. It is they which uplift and recreate
the lands which the agents of denudation are continually
destroying; it is they which deepen the ocean bed and thus
withdraw its waters from the shores. At times also these forces
have aided in the destruction of the lands by gradually lowering
them and bringing in the sea. Under the action of forces resident
within the earth the crust slowly rises or sinks; from time to
time it has been folded and broken; while vast quantities of
molten rock have been pressed up into it from beneath and
outpoured upon its surface. We shall take up these phenomena in
the following chapters, which treat of upheavals and depressions
of the crust, foldings and fractures of the crust, earthquakes,
volcanoes, the interior conditions of the earth, mineral veins,
and metamorphism.