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Jacques W. (Jacques Wardlaw) Redway.

Elementary physical geography : an outline of physiography online

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Like most other elevations of the earth's surface, pla-
teaus are the result of a gradual uplift of parts of the rock
envelope. Most of the great plateaus of the earth are
rimmed by lofty mountain-ranges, and their surfaces are
generally traversed by ridges and valleys. Thus, the pla-
teau region of western North America, nearly a mile and
a half high, is bordered by the lofty ranges of the Eocky
Mountains; and Sierra Nevada systems ; the great Boliv-
ian plateau is margined by the highest summits of the
Andes ; and the loftiest plateau in the world, that of Tibet,
is enclosed by some of the loftiest ranges of the earth.

Mesas and table-lands are generally the result of ero-
sion, or unequal weathering. The top of the mesa is com-
monly a layer of rock resting upon softer substance. The
latter is protected from the action of the elements by the
harder material and, in time a talile-land is formed. With-
out the hard cap the surface would have been rounded off,
leaving a hill instead of a mesa. As a rule, mesas and
table-lands are the outlying or isolated remnants of pla-
teaus. They are noticeable objects because of their flat tops
and the steep cliffs or escarpments that form their slopes.



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Kanab Plateau



Canon of Kanab River



Kaibab Plateau









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Echo Cliffs



64 PHYSICAL GEOGRAPHY

Distribution of Plateaus. — Most of the high plateaus
are in the great highlands that radiate from north circum-
polar regions ; they face the Pacific and Indian Oceans.
A series of lesser highlands borders the Atlantic Ocean,
and these also contain plateaus. Although the plateaus
have each a more or less definite outline they cannot al-
ways be considered apart from the highlands to which
they belong. In places where the highlands border the
sea, the plateaus may take the form of peninsulas ; name
several examples on the map of Asia.

Among the plateaus of the Asian Continent, that of
Tibet is remarkable for its size and elevated sui'face, near-




A DISSECTED PLATEAU, JOHN DAY VALLEY, OREGON

The sheet of lava at the surface has been removed here and there, leaving- a scries of mesas.

\y three miles above sea-level ; by what ranges is it partly
enclosed ? To the westward are the Pamirs, a series of
grassy plateaus, like the "parks " of Colorado, about three
and a half miles above the sea. In North America, the
plateaus of the Avestern highlands are a little more than a
mile high, while those of the eastern highland have less
than half that altitude. In South America the plateaus of
the Andes are about two miles high, while those of the
eastern region have less than one-third that height.

Economic Aspect of Plateaus. — Plateaus, especially
those of a considerable altitude, are generally unproduc-
tive. In some instances they are so high that but little
rain falls; in others the mountain rims shut off the moist-
ure that is borne with the winds. The rugged slopes and
deep canons almost always make commercial intercourse



PLAINS, PLATEAUS, AND MOUNTAINS 65



very difficult, and sometimes impossible, except to the
rudest methods of communication. Because of their un-
productive character the high plateaus, as a rule, are
sparsely peopled ; and because of the lack of intercommu-
nication the civilization of the native peoples is not usu-
ally of the highest type.

In the lower plateaus the conditions are different;
there is generally a rainfall sufficient for the production of
food-stuffs, and the land that cannot be cultivated is often
well adapted to grazing ; meat, cattle products and wool
are almost always associated with these plateaus. The
broken and dissected rock strata in many instances yield
minerals and metallic ores useful in the arts and sciences,
and the rugged character of the surface often furnishes an
abundance of water-power. In the New England Plateau
of the United States one may see the results of surface
conditions in the production of water-power ; in the Ap-
palachian Plateaus, the results of coal and iron produc-
tion ; and in the Iberian Plateau and Australia the re-
sults of grazing facilities. The avooI from these regions is
the finest in the world.

Mountains. — Mountains are the most characteristic
and remarkable features of the landscape. In form, they




A SECTION ACROSS THE UINTA MOUNTAINS
^ siiig/c fold with fault. 'After Pozuctl.



are great ridges marked by a very rugged surface. In
structure, tlnsy are folds or wrinkles in the strata of the
rock envelope, or else they are immense blocks of rock,
broken and partly upturned.



66



PHYSICAL GEOGRAPHY



Mountains occur usually in sysfeins, each of which con-
sists of many ranges, together forming a distinct group.
A very extensive system is sometimes called a cordillera.
Thus, the Rocky and Andean S3'stems from the great
Cordillera of the Western Continent Ranges or folds that
seem to be continuations, one of the other, are said to be
a chain, as the Sierra Nevada and Cascade Mountains. A
single fold may be worn away so that the broken strata
form ridges ; or the crest may be weathered so unevenly
that it presents the appearance of a series of notches,
thereby forming a sierra. Any part of the crest or summit

materially higher
t h a n the rest
forms a peak. '"
In most instances
the peak is a high
crag, or a pinna-
cle, but the name
is also ap|)lied to
volcanic cones,
and to elevations
that more prop-
erly are plateaus — as Broad Mountain, Pocono Moun-
tain, and Broad Top, in the Appalachian system.

A mountain system is characterized generally by great
extent, several of the more important exceeding four or five
thousand miles in length. Name three of the greatest
systems. A range, on the contrary, rarely exceeds a few
hundred miles in length. It gradually takes form, contin-
ues a short distance, and then disappears, another to the
right or the left taking its place. The rolling hills that in
many instances form the approach to a system, are called
foot-hills or, better, Piedmont lands. The hollow or de-
pression between adjacent ranges forms an intermontane




•THE JURA MOUNTAINS
o4 series of goitle folds.



PLAINS, PLATEAUS, AND MOUNTAINS 67

valley ; or if wide and apparently enclosed, a park. A
valley that extends across the range is called a pass, a gap,
or a canon.

Nature of Mountain Ranges. — In the simplest form,
as the Uinta Mountains, there is a single fold ; in the Jura




■u' - . - 1. ■ ■ ^ t - - _™



SECTION OF A DISSECTED RANGE
t,4 %inglc fold IS dissected into a number of ridges.

Mountains there are several ; in other instances, as the
Alps, there has been a mashing anel crumpling of the
strata, producing results as irregular and complex as though
the leaves of a book had been pressed and crumpled side-
waj's by a great force.

The folding process takes place slowly — so slowl}', in
fact, that no means exist Avhereby it can be measured ex-
cept after long intervals of time. This is shown by the
conduct of certain rivers that flow across the folds. The
streams cut their channels downward quite as fast as the
folds are pushed upward. So Avhen the fold has become a
lofty range, it is severed transversely by the stream. Had
not the ui)thrust of the fold proceeded more slowly than the
downward cutting of the stream, the latter would be
turned aside ; in places this seems to have occurred, but
even in such cases there is always evidence that the uplift
of the range is very slow.



68



PHYSICAL GEOGRAPHY



Excepting the core of granite, or similar rock that is
present in the lower part of many folds, mountain-ranges
are composed of strata of sedimentary rock. Moreover, it
is a notable fact that the strata which form them are much
thicker along the folds than elsewhere." Thus in the
Appalachian Mountains, the sediments composing the
folds are about 40,000 feet thick, while the same strata
in the Mississippi Valley are scarcely more than 4,000
feet in thickness.

Not all ranges present the aspects of folds, however.
The ridges in the Great Basin of the United States are
great blocks of sedimentary rocks that have been broken
and tilted, and left with edges partly upturned. The
Sierra Nevada and Cascade Eanges are both folded and
broken, and their abrupt eastern slope is the edge of an
immense block tilted toward the Pacific.




BLOCK MOUNTAINS, BASIN REGION
The upturned edges form the ranges.

The ideal system with its parallel folds exists, it is true,
but it is not common. In most instances one finds a con-
fused tangle of ridges and ranges, separated by intermon-
tane valleys and crossed by gaps and passes. In not a few
instances parallel ranges are connected by spurs, as in the



PLAINS, PLATEAUS, AND MOUNTAINS 69

Sierra Nevada and Coast Ranges ; and not infrequently
several ranges seem to radiate from a massive uplift, as in
the case of the Pamir highland, from which radiate the
great folds that form the Himalaya, Tian Shan, Hindu
Kush, and Suliman Mountains.

Physiographic Aspect of Mountains.— From the mo-
ment the process of uplift begins the waters of the atmos-
phere begin to level oif the folds. In general, the more
prominent a topographic feature, the more exposed will it
be to the factors that produce erosion. And although
nearly every part of the rock envelope is undergoing denu-
dation, uplifted surfaces generally suffer most. As the
process of elevation goes on, the mountain torrents carve
the slopes of the range into a multitude of valleys, canons,
ridges, and hogbacks.

Not only are the flanks sculptured, but the crests are
also worn away. The tops of the folds being considerably
broken and, at the same time, the most exposed, little by
little are removed, leaving the upturned edges in the form
of long 7'id(jes. Most of the ranges of the Appalachian
Mountains are ridges formed in this manner; there are
few folds, but many ridges.

The amount of material removed from the slopes and
crests of mountains is enormous. The crests of the Ap-
palachian folds in Pennsylvania are scarcely more than
two thousand feet high at the present time ; but if all the
material that has been removed could be again heaped
upon them, their summits would be not far from ten miles
high — about twice as high as the loftiest summits of the
Himalayan folds. Usually the slopes and foot-hills are
covered deep with coarse rock waste. '^

Much — probal)ly most — of this material has been re-
moved by running water, but the moving ice sheet that at
one time covered the northern part of the Appalachian



70 PHYSICAL GEOGRAPHY

higlikiiKls wiis also a |)owerful agent in sculpturing their
crests and slopes. Thus, in the North Atlantic States and
New York, where they received the full force of glacial ice,
the highlands, in places, are worn down almost to the sea-
level. In Pennsylvania, where the wasting was less ef-
fective, they are about two thousand feet high. But in
the South Atlantic States, beyond the limits of glacial
ice, the various ridges are more than four thousand feet in
altitude.

As a rule, therefore, mountain-ranges which show l)ut few
effects of weathering are comparatively young. The tilted
blocks of strata that constitute the short ranges of eastern
Oregon as yet are scarcely notched by streams, and are
very slightly weathered. The ridges of Nevada are much
more worn and carved, and the Kocky Mountains, though
young as compared with the Appalachian folds, are very
much worn. The Laurentian folds, the oldest in North
America, are worn so greatly that their highest crests are
only a few hundred feet above sea-level.

The character of the Aveathering and the landscape
scenery as Avell depend partly on the rock and partly on
the conditions of climate. In the Appalachian ranges all
the forms are rounded, subdued, and graceful. In arid
regions they are apt to be angular. The notched crests of
western ranges of the United States and Mexico have sug-
gested the name " sierra " (saw), the sharp, enduring crags
of the Alps, " aiguille " (needle), " horn," and " dent " (tooth).

Distribution of Mountains. — Mountain-ranges seem to
be incidental to highland regions. The great highlands
that border the Pacific and Indian Oceans are rimmed
throughout much of their extent by very lofty folds. In
North America the Eocky and Sierra Nevada ranges are
the rims of a high plateau whose surface is traversed by
block ranges.



PLAIjSS, plateaus, and mountains 71

How is this statement borne out in the case of South
America ? of AustraHa ? of Africa ? It does not seem ap-
parent, however, in the case of Eurasia. The great system
of southern Eiu'ope, extending from the Caspian Sea to the
Atlantic, belongs to the principal highland of Eurasia.
The Alps form the northern, and the Atlas Ranges of
Africa the southern rim. What sea fills the intermon-
tane valley between them? A partly submerged chain
extends along the east coast of Asia ; name the peuin-
sulas aud princi})al island groups belonging to it. In
general the great systems are nearest the Pacific and Ind-
ian Oceans.

Valleys.— The folding of strata into paralleb ranges
naturally forms valleys between them. The great inter-
montane valley of California, Oregon, and "Washington is
of this character. Name the ranges between which it is
situated. Although interrupted by cross ranges it prac-
tically extends from Puget Sound to the Gulf of Califor-
nia. The valley, a part of which the St. Lawrence River
now occupies, is similar in structure.

Most valleys, however, are the results of stream-cutting
and the general weathering that comes from the action of
water. Shenandoah Valley, the depression crossing Vir-
ginia, is an example. The rocks along the line of the val-
ley were more easily worn away than those to the east
and the west, and hence the valley resulted from their re-
moval. The valley of the lower Hudson was possibly
formed in a similar manner.'''

Li many instances the water wears away the broken
rocks forming the crest of a range more easil}' than it can
remove them elsewher(;. hi this way ccmoe-shaped VftUci/s
are formed at the summit of a fold. More commonly,
however, the streams on o[)|)Osite sides of a rang(! wear
their channels ckiar to the crest, partly breaking the lat-



72



PHYSICAL GEOGRAPHY



ter down by making deep notches across it. Many of the
passes in the Sierra Nevada and Rocky Mountains are ex-
amples ; ^" and so, too, are the water-gaps of the Delaware,
Susquehanna, and Hudson Rivers. Water-gaps are usually
at the base level of the range ; passes are usually high
above it.




CANOE VALLEVS, APPALACHIAN MOUNTAINS

In a few instances the cross spurs that join parallel
ranges enclose valleys of considerable extent. The Parks
of Colorado, and the Pamirs, both frequently classed
among plateaus, are exam])les. The latter are situated in
a high mountain knot which, because of its great height,
is often called the " Roof of the World."

Economic Aspect of Mountains. — Notwithstanding
the fact that mountains are sparsely settled, and include a
very large proportion of uncultivable land, they neverthe-
less exert a great influence on life, its history, and its in-
dustries. Ranges that face rain -bearing winds may be so
lofty that they intercept all tlie moisture. How do the
Cascade and Sierra Nevada ranges illustrate this ? How
does this affect the habitability of the region west of their
summits? In various localities ranges at a considerable
distance from the sea chill the Avinds passing over them
and condense the moisture that otherwise would not be
precipitated. Mountains, therefore, are factors in the dis-
tribution of rain.



PLAINS, PLATEAUS, AND MOUNTAINS 73

The broken folds of the strata frequently expose metals
and minerals that otherwise would not be accessible. Al-
most all the gold and silver, the mechanism of exchange,
come from mountain-ranges ; and so, also, does most of
the copper, a metal necessary in the transmission of elec-
tric power. Practically all the anthracite coal and much
of the best iron ores are associated with the rocks of
mountain-ranges. The latter are, therefore, essential to
the industries of mankind.

Mountains atiect life and its industries mainly because
they are barriers to intercommunication. The Greek peo-
ples of early times found it much easier to spread along
the shores of the Mediterranean and across the ^Egean
Sea than to cross the Balkan Mountains. For the first
fifty years of our national history there was no transcon-
tinental intercourse between the Atlantic and Pacific
coasts of our country. It was easier to go sixteen thou-
sand miles around Ctipe Horn than to traverse one thou-
sand miles of mountainous surface.

The efl'ects of intercommunication may be seen in the
case of the Basques. More than two thousand years ago
they were driven from the lowlands of Spain and France
into the almost inaccessible valleys of the Pyrenees Moun-
tains. During the succeeding years they have been so little
in contact with the rest of the world that their language
and customs have been changed but little in that time.

Because of the dift'erences of climate on opposite sides
of high ranges, the distribution of life-forms is greatly re-
stricted. The dense forests of the Pacific Coast can-
not extend across the Cascade and Sierra Nevada Ranges,
because there is not enough moisture to support them.
On the other hand, not many of the plants of the arid side
of the mountains can cross the ranges and survive because
the conditions of climate and soil are unsuitable.










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PLAINS, PLATEAUS, AND MOUNTAINS 75

lutermoutaue valleys are usually productive, and there-
fore densely i^eopled, areas. As a rule, their fertility can-
not be easily impaired, because fresh soil is brought to
them with every flood season. Because of the infertile
region on either side, the industries of life are of neces-
sity concentrated in the valleys.

Passes have even greater importance than valleys. A
mountain-range is an obstacle to communication, and the
pass is, therefore, the channel toward which intercourse
must be concentrated. Kailway routes through mountain-
ous regions are always surveyed and built through the
passes. Almost every railway to the various commercial
centres of the Atlantic seaboard seeks a way through the
passes and water-gaps of the Appalachian Mountains.

To Mohawk Gap, a pass that practically forms the
principal route of traffic between the Great Lakes and
the Hudson Eiver, the wonderfvil development of New
York City is due. It is more nearly level than any other
route across the Appalachian Mountains, and for this rea-
son it furnishes a standard by which freight rates between
Atlantic seaports and the Mississippi basin are regulated,

Khyber Pass, a narrow defile a few miles east of Kabul,
for more than two thousand years has been a part of one
of the great overland routes between Europe and India.
Indeed, it is the chief gateway to India ; and the truth of
the old saying, " whoso would be master of India must
first make himself Lord of Kabul," is every day more and
more emphasized. It is evident, therefore, that inasmuch
as mountains are a barrier between peoples upon their op-
posite sides, all the intercourse and communication must
be concentrated at the passes.

QUESTIONS AND EXERCISES. Name and classify the vertical
forms in the State in which you live. On an outline map, shade or oth-
erwise designate the areas of highland and lowland, using such contours.



76 PHYSICAL GEOGRAPHY

or lines of equal altitude, as may be available. If possible use the Re-
lief Map of the United States noted below.

Make a relief model in sand or paper pulp of any locality, the topog-
raphy of which you know— State, county, township, or other region
of interest.

What results might occur were a mountain fold to be formed across
the channel of a river ?

Make a sketch restoring the plateau or mesa dissected by weathering
processes, as shown on p. 64.

Name some of the benefits and the disadvantages resulting from the
presence of the Appalachian Mountains between the industrial centres
of the Atlantic Coast and the Mississippi Valley.

Explain why Fort Ticonderoga and Crown Point were important
localities during the colonial wars. {Consult any good map of Lake
Champlain.)

On an outline map of each continent, or grand division, draw heavy
lines representing the positions of the principal mountain-ranges.

In what general direction does the rock waste of mountains move ? —
Explain why.

Give reasons why lowlands are more densely peopled than high-
lands.

COLLATERAL READING AND REFERENCE

McGee. — The Piedmont Plateau, National Geographic Mag-
azine, vii, 201 .

Willis. — Physiography of the United States, pp. 169-202.

HAYE.S. — Physiography of the United States, pp. 305-336.

Powell. — Exploration of Grand Canon, pp. 181-193.

United States Geological Survey Maps, the following
jsheets : Tooele, Marion, Sierraville, Marysville, Kaibab, Farmer-
^'ille, Spottsj'lvania, Mount Monadnock, Mount Mitchell, Hum-
melstown, and others.

NOTES

' The difiference in the surface features of these plains is due
partly to altitude and partly to rainfall. The Pampas resemble
the high plains east of the Rocky Mountains. Both slope from a
high to a low level, and both are covered with " bunch-grass" —
that of the Pampas being a very coarse species that grows to a



PLAINS, PLATEAUS, AND MOUNTAINS 77

height of four or five feet. The Llanos are watered by periodical
rains and ai'e alternately a swamp and a sun-baked desert. The
Silvas lie in a region of almost constant equatorial rains ; hence
they are adapted to tropical forestry. The Pampas and Llanos
produce wild cattle and horses ; the Silvas, rubber and ornamental
woods.

" It will be swept by simoon winds because it will be practically
a desert, for it is in such regions only that simoon winds are
found. The same is true of the valley of Great Salt Lake : it
will be a desert region as soon as the lake disappears.

' Alluvial plains are the most productive lands in the world.
Because their soil is constantly replenished by overflows and
freshets they rarely wear out ; the nutrient elements are sup-
plied about as fast as they are exhausted.

* The Atlantic Coast Plain varies from a few miles to more than
one hundred in width. The more recently formed parts are cov-
ered with pines ; and a broken, narrow belt of pine forest extends
from Chesapeake Bay almost to the Rio Grande. To the east-
ward of the pine barrens is a belt of sand flats and swamps of still
more recent origin.

" Diluvial plains in places are strewn with large bowlders and
covered with a " drift " composed of sand, unsorted gravel, clay,
and bowlders.

'A similar plain involves the northern part of North America.
In the New World, however, it loses many of the topographic
features of a plain and is, perhaps more accurately, a low, but
rugged plateau. Its slope, however, like that of the Eurasian
plain, is toward the Arctic Ocean, and like the latter plain, its
coastal portion is bordered by tundras. Generallj- considered,
this plain is a vast basin almost shutting the Arctic Ocean from
the rest of the sea.

' Plains are quite as subject to the same weathering processes
as are mountains and plateaus, but because of their gentler
slopes, the rate of erosion is not so great as in mountainous
regions. The bluff lands along the Mississippi and some of its
tributaries are thus dissected. Their complete degradation is a
matter of time only. The higher parts of the Atlantic Coast
Plain have l)een also greatly dissected by streams. In many in-



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