The four great physical divisions of North America--the Laurentian
highland, the Appalachian highland, the plains, and the western
cordillera--are strikingly different in form and structure. The
Laurentian highland presents a monotonous waste of rough hills,
irregular valleys, picturesque lakes, and crooked rivers. Most of it
is thinly clothed with pine trees and bushes such as the blueberry
and huckleberry. Yet everywhere the ancient rock crops out. No one can
travel there without becoming tiresomely familiar with fine-grained,
shattered schists, coarse granites, and their curiously banded
relatives, the gneisses. This rocky highland stretches from a little
north of the St. Lawrence River to Hudson Bay, around which it laps in
the form of a V, and so is known as the Archaean V or shield.
Everywhere this oldest part of the Western Hemisphere presents
unmistakable signs of great age. The schists by their fine crumpling and
scaly flakes of mineral show that they were formed deep in the bowels
of the earth, for only there could they be subjected to the enormous
pressure needed to transform their minerals into sheets as thin as
paper. The coarse granites and gneisses proclaim still more clearly that
they must have originated far down in the depths of the earth; their
huge crystals of mica, quartz, hornblende, feldspar, and other minerals
could never have been formed except under a blanket of rock which almost
prevented the original magmas from cooling. The thousands or tens of
thousands of feet of rock which once overlay the schists and still more
the granites and gneisses must have been slowly removed by erosion, for
there was no other way to get rid of them. This process must have
taken tens of millions of years, and yet the whole work must have been
practically completed a hundred or perhaps several hundred million years
ago. We know this because the selfsame ancient eroded surface which
is exposed in the Laurentian highland is found dipping down under the
oldest known fossiliferous rocks. Traces of that primitive land surface
are found over a large part of the American continent. Elsewhere they
are usually buried under later strata laid down when the continent
sank in part below sea-level. Only in Laurentia has the land remained
steadily above the reach of the ocean throughout the millions of years.
Today this old, old land might be as rich as many others if climate
had been kind to it. Its soil, to be sure, would in many parts be sandy
because of the large amount of quartz in the rocks. That would be a
small handicap, however, provided the soil were scores of feet deep like
the red soil of the corresponding highland in the Guiana region of
South America. But today the North American Laurentia has no soil worth
mentioning. For some reason not yet understood this was the part
of America where snow accumulated most deeply and where the largest
glaciers were formed during the last great glacial period. Not once but
many times its granite surface was shrouded for tens of thousands of
years in ice a mile or more thick. As the ice spread outward in almost
every direction, it scraped away the soil and gouged innumerable hollows
in the softer parts of the underlying rock. It left the Laurentian
highland a land of rocky ribs rising between clear lakes that fill the
hollows. The lakes are drained by rapid rivers which wind this way
and that in hopeless confusion as they strive to move seaward over the
strangely uneven surface left by the ice. Such a land is good for the
hunter and trapper. It is also good for the summer pleasure-seeker who
would fain grow strong by paddling a canoe. For the man who would make
a permanent home it is a rough, inscrutable region where one has need of
more than most men's share of courage and persistence. Not only did
the climate of the past cause the ice to scrape away the soil, but
the climate of the present is so cold that even where new soil has
accumulated the farmer can scarcely make a living.
Around the borders of the Laurentian highland the ice accomplished a
work quite different from the devastation of the interior. One of its
chief activities was the scouring of a series of vast hollows which
now hold the world's largest series of lakes. Even the lakes of Central
Africa cannot compare with our own Great Lakes and the other smaller
lakes which belong to the same series. These additional lakes begin
in the far north with Great Bear Lake and continue through Great Slave
Lake, Lake Athabasca, and Lake Winnipeg to the Lake of the Woods, which
drains into Lake Superior. All these lakes lie on the edge of the great
Laurentian shield, where the ice, crowding down from the highland to
the north and east, was compressed into certain already existent hollows
which it widened, deepened, and left as vast bowls ready to be filled
with lakes.
South and southwest of the Laurentian highland the great ice sheet
proved beneficial to man. There, instead of leaving the rock naked,
as in the Laurentian region, it merely smoothed off many of the
irregularities of the surface and covered large areas with the most
fertile soil.
In doing this, to be sure, the ice-cap scoured some hollows and left a
vastly larger number of basins surrounded in whole or in part by glacial
debris. These have given rise to the innumerable lakes, large and small,
whose beauty so enhances the charms of Canada, New England, New York,
Minnesota, and other States. They serve as reservoirs for the water
supply of towns and power plants and as sources of ice and fish. Though
they take land from agriculture, they probably add to the life of
the community as much in other ways as they detract in this. Moreover
glaciation diverted countless streams from their old courses and made
them flow over falls and rapids from which water-power can easily be
developed. That is one reason why glaciated New England contains over
forty per cent of all the developed water-power in the United States.
Far more important, however, than the glacial lakes and rivers is the
fertile glacial soil. It comes fresh from the original rocks and has not
yet been exhausted by hundreds of thousands of years of weathering.
It also has the advantage of being well mixed, for generally it is the
product of scrapings from many kinds of rocks, each of which contributes
its own particular excellence to the general composition. Take Wisconsin
as an example. * Most parts of that State have been glaciated, but in
the southwest there lies what is known as the "driftless area" because
it is not covered with the "drift" or glacial debris which is thickly
strewn over the rest of the State. A comparison of otherwise similar
counties lying within and without the driftless area shows an
astonishing contrast. In 1910 the average value of all the farm land in
twenty counties covered with drift amounted to $56.90 per acre. In six
counties partly covered with drift and partly driftless the value was
$59.80 per acre, while in thirteen counties in the driftless area it was
only $33.30 per acre. In spite of the fact that glaciation causes swamps
and lakes, the proportion of land cultivated in the glaciated areas is
larger than in the driftless. In the glaciated area 61 per cent of the
land is improved and in the driftless area only 43.5 per cent. Moreover,
even though the underlying rock and the original topography be of the
same kind in both cases, the average yield of crops per acre is greater
where the ice has done its work. Where the country rock consists of
limestone, which naturally forms a rich soil, the difference in favor
of the glaciated area amounts to only 1 or 2 per cent. Where the country
rock is sandy, the soil is so much improved by a mixture of fertilizing
limestone or even of clay and other materials that the average yield
of crops per acre in the glaciated areas is a third larger than in the
driftless. Taking everything into consideration it appears that the
ancient glaciation of Wisconsin increases the present agricultural
output by from 20 to 40 per cent. Upwards of 10,000,000 acres of
glaciated land have already been developed in the most populous parts of
the State. If the average value of all products on this area is reckoned
at $15 per acre and if the increased value of agricultural products due
to glaciation amounts to 30 per cent, then the net value of glaciation
per year to the farmers of Wisconsin is $45,000,000. This means about
$300 for each farmer in the glaciated area.
* R. H. Whitbeck, "Economic Aspects of Glaciation in Wisconsin",
in "Annals of the Association of American Geographers," vol. III in
(1913), pp. 62-67.
Wisconsin is by no means unique. In Ohio, for instance, there is also
a driftless area. * It lies in the southeast along the Ohio River. The
difference in the value of the farm land there and in the glaciated
region is extraordinary. In the driftless area the average value per
acre in 1910 was less than $24, while in the glaciated area it was
nearly $64. Year by year the proportion of the population of the State
in the unglaciated area is steadily decreasing. The difference between
the two parts of the State is not due to the underlying rock structure
or to the rainfall except to a slight degree. Some of the difference is
due to the fact that important cities such as Cleveland and Toledo lie
on the fertile level strip of land along the lake shore, but this strip
itself, as well as the lake, owes much of its character to glaciation.
It appears, therefore, that in Ohio, perhaps even more than in
Wisconsin, man prospers most in the parts where the ice has done its
work.
* William H. Hess, "The Influence of Glaciation in Ohio," in
"Bulletin of the Geographical Society of Philadelphia," vol. XV (1917),
pp. 19-42.
We have taken Wisconsin and Ohio as examples, but the effect of
glaciation in those States does not differ materially from its effect
all over southern Canada and the northern United States from New England
to Kansas and Minnesota. Each year the people of these regions are
richer by perhaps a billion dollars because the ice scraped its way down
from Laurentia and spread out over the borders of the great plains on
the west and of the Appalachian region on the east.
We have considered the Laurentian highland and the glaciation which
centered there. Let us now turn to another highland only the northern
part of which was glaciated. The Appalachian highland, the second great
division of North America, consists of three parallel bands which extend
southwestward from Newfoundland and the St. Lawrence River to Georgia
and Alabama. The eastern and most important band consists of hills and
mountains of ancient crystalline rocks, somewhat resembling those of the
Laurentian highland but by no means so old. West of this comes a broad
valley eroded for the most part in the softer portions of a highly
folded series of sedimentary rocks which are of great age but younger
than the crystalline rocks to the east. The third band is the Alleghany
plateau, composed of almost horizontal rocks which lie so high and have
been so deeply dissected that they are often called mountains.
The three Appalachian bands by no means preserve a uniform character
throughout their entire length. The eastern crystalline band has its
chief development in the northeast. There it comprises the whole of New
England and a large part of the maritime provinces of Canada as well as
Newfoundland. Its broad development in New England causes that region to
be one of the most clearly defined natural units of the United States.
Ancient igneous rocks such as granite lie intricately mingled with old
and highly metamorphosed sediments. Since some of the rocks are hard and
others soft and since all have been exposed to extremely long erosion,
the topography of New England consists typically of irregular masses
of rounded hills free from precipices. Here and there hard masses of
unusually resistant rock stand up as isolated rounded heights, like
Mount Katahdin in Maine. They are known as "monadnocks" from the
mountain of that name in southern New Hampshire. In other places larger
and more irregular masses of hard rock form mountain groups like the
White Mountains, the Green Mountains, and the Berkshires, each of which
is merely a great series of monadnocks.
In the latitude of southern New York the crystalline rocks are
compressed into narrow compass and lose their mountainous character.
They form the irregular hills on which New York City itself is built and
which make the suburbs of Westchester County along the eastern Hudson
so diverse and beautiful. To the southeast the topography of the old
crystalline band becomes still less pronounced, as may be seen in the
rolling, fertile hills around Philadelphia. Farther south the band
divides into two parts, the mountains proper and the Piedmont plateau.
The mountains begin at the Blue Ridge, which in Virginia raises its
even-topped heights mile after mile across the length of that State. In
North Carolina, however, they lose their character as a single ridge
and expand into the broad mass of the southern Appalachians. There Mount
Mitchell dominates the eastern part of the American continent and is
surrounded by over thirty other mountains rising to a height of at least
six thousand feet. The Piedmont plateau, which lies at the eastern foot
of the Blue Ridge, is not really a plateau but a peneplain or ancient
lowland worn almost to a plain. It expands to a width of one hundred
miles in Virginia and the Carolinas and forms the part of those States
where most of the larger towns are situated. Among its low gentle
heights there rises an occasional little monadnock like Chapel Hill,
where the University of North Carolina lies on a rugged eminence which
strikingly recalls New England. For the most part, however, the hills
of the Piedmont region are lower and more rounded than those in
the neighborhood of Philadelphia. The country thus formed has many
advantages, for it is flat enough to be used for agriculture and yet
varied enough to be free from the monotony of the level plains.
The prolonged and broken inner valley forming the second band of the
Appalachians was of some importance as a highway in the days of the
Indians. Today the main highways of traffic touch it only to cross it as
quickly as possible. From Lake Champlain it trends straight southward in
the Hudson Valley until the Catskills have been passed. Then, while the
railroads and all the traffic go on down the gorge of the Hudson to
New York, the valley swings off into Pennsylvania past Scranton,
Wilkesbarre, and Harrisburg. There the underlying rock consists of a
series of alternately hard and soft layers which have been crumpled up
much as one might wrinkle a rug with one's foot. The pressure involved
in the process changed and hardened the rocks so much that the coal
which they contain was converted into anthracite, the finest coal in all
the world and the only example of its kind. Even the famous Welsh coal
has not been so thoroughly hardened. During a long period of erosion the
tops of the folded layers were worn off to a depth of thousands of feet
and the whole country was converted into an almost level plain. Then
in the late geological period known as the early Tertiary the land was
lifted up again, and once more erosion went on. The soft rocks were thus
etched away until broad valleys were formed. The hard layers were left
as a bewildering succession of ridges with flat tops. A single ridge
may double back and forth so often that the region well deserves the old
Indian name of the "Endless Mountains." Southwestward the valley grows
narrower, and the ridges which break its surface become straighter.
Everywhere they are flat-topped, steep-sided, and narrow, while between
them lie parts of the main valley floor, flat and fertile. Here in the
south, even more clearly than in the north, the valley is bordered
on the east by the sharply upstanding range of the crystalline
Appalachians, while on the west with equal regularity it comes to an end
in an escarpment which rises to the Alleghany plateau.
This plateau, the third great band of the Appalachians, begins on the
south side of the Mohawk Valley. To the north its place is taken by
the Adirondacks, which are an outlier of the great Laurentian area of
Canada. The fact that the outlier and the plateau are separated by the
low strip of the Mohawk Valley makes this the one place where the highly
complex Appalachian system can easily be crossed. If the Alleghany
plateau joined the Adirondacks, Philadelphia instead of New York would
be the greatest city of America. Where the plateau first rises on the
south side of the Mohawk, it attains heights of four thousand feet in
the Catskill Mountains. We think of the Catskills as mountains, but
their steep cliffs and table-topped heights show that they are really
the remnants of a plateau, the nearly horizontal strata of which
have not yet been worn away. Westward from the Catskills the plateau
continues through central New York to western Pennsylvania. Those who
have traveled on the Pennsylvania Railroad may remember how the railroad
climbs the escarpment at Altoona. Farther east the train has passed
alternately through gorges cut in the parallel ridges and through
fertile open valleys forming the main floor of the inner valley. Then it
winds up the long ascent of the Alleghany front in a splendid horseshoe
curve. At the top, after a short tunnel, the train emerges in a wholly
different country. The valleys are without order or system. They wind
this way and that. The hills are not long ridges but isolated bits left
between the winding valleys. Here and there beds of coal blacken the
surface, for here we are among the rocks from which the world's largest
coal supply is derived. Since the layers lie horizontally and have never
been compressed, the same material which in the inner valley has been
changed to hard, clean-burning anthracite here remains soft and smoky.
In its southwestern continuation through West Virginia and Kentucky
to Tennessee the plateau maintains many of its Pennsylvanian
characteristics, but it now rises higher and becomes more inaccessible.
The only habitable portions are the bottoms of the valleys, but they are
only wide enough to support a most scanty population. Between them most
of the land is too rough for anything except forests. Hence the people
who live at the bottoms of the valleys are strangely isolated. They see
little or nothing of the world at large or even of their neighbors. The
roads are so few and the trails so difficult that the farmers cannot
easily take their produce to market. Their only recourse has been to
convert their bulky corn into whisky, which occupied little space in
proportion to its value. Since the mountaineer has no other means of
getting ready money, it is not strange that he has become a moonshiner
and has fought bitterly for what he genuinely believed to be his rights
in that occupation. Education has not prospered on the plateau because
the narrowness of the valleys causes the population to be too poor and
too scattered to support schools. For the same reason feuds grow up.
When people live by themselves they become suspicious. Not being used to
dealing with their neighbors, they suspect the motives of all but their
intimate friends. Moreover, in those deep valleys, with their steep
sides and their general inaccessibility, laws cannot easily be enforced,
and therefore each family takes the law into its own hands.
Today the more rugged parts of the Appalachian system are chiefly
important as a hindrance to communication. On the Atlantic slope of the
old crystalline band there are great areas of gentle relief where an
abundant population can dwell. Westward on the edges of the plateau and
the plains beyond a still greater population can find a living, but in
the intervening space there is opportunity for only a few. The great
problem is to cross the mountains as easily as possible. Each accessible
crossing-place is associated with a city. Boston, as well as New York,
owes much to the low Mohawk-Hudson route, but is badly handicapped
because it has no easy means of crossing the eastern crystalline band.
Philadelphia, on the other hand, benefits from the fact that in its
vicinity the crystallizes are low and can readily be crossed even
without the aid of the valleys of the Delaware and Schuylkill rivers.
It is handicapped, however, by the Alleghany escarpment at Altoona, even
though this is lower there than farther south. Baltimore, in the same
way, owes much of its growth to the easy pathways of the Susquehanna
on the north and the Potomac on the south. Farther south both the
crystalline band and the Alleghany plateau become more difficult to
traverse, so that communication between the Atlantic coast and the
Mississippi Valley is reduced to small proportions. Happy is New York
in its situation where no one of the three bands of the Appalachians
opposes any obstacle. The plains of North America form the third of the
four main physical divisions of the continent. For the most part they
lie between the great western cordillera on one side and the Laurentian
and Appalachian highlands on the other. Yet they lap around the southern
end of the Appalachians and run far up the Atlantic coast to New York.
They remained beneath the sea till a late date, much later than the
other three divisions. They were not, however, covered with deep water
like that of the abysmal oceans, but only with shallow seas from which
the land at times emerged. In spite of the old belief to the contrary,
the continents appear to be so permanent that they have occupied
practically their present positions from the remotest geological times.
They have moved slowly up and down, however, so that some parts have
frequently been submerged, and the plains are the parts that remained
longest under water.
The plains of North America may be divided into four parts according
to the character of their surface: the Atlantic coastal plain, the
prairies, the northwestern peneplain, and the southwestern high plains.
The Atlantic coastal plain lies along the Atlantic coast from New York
southward to Florida and Alabama. It also forms a great embayment up the
Mississippi Valley as far as the Ohio River, and it extends along the
shore of the Gulf of Mexico to the Rio Grande. The chief characteristic
of this Atlantic and Gulf coastal plain is its belted nature. One layer
of rocks is sandy, another consists of limestone, and a third of clay.
When uplifted and eroded each assumes its own special topography and is
covered with its own special type of vegetation. Thus in South Carolina
and Georgia the crystalline Piedmont band of the Appalachian province
is bordered on the southeast by a belt of sandstone. This rock is so
far from the sea and has been raised so high above it that erosion has
converted it into a region of gentle hills, whose tops are six hundred
or seven hundred feet above sea-level. Its sandy soil is so poor that
farming is difficult. The hills are largely covered with pine, yielding
tar and turpentine. Farther seaward comes a broad band of younger rock
which forms a clayey soil or else a yellow sandy loam. These soils are
so rich that splendid cotton crops can be raised, and hence the region
is thickly populated. Again there comes a belt of sand, the so-called
"pine barrens," which form a poor section about fifty miles inland from
the coast. Finally the coastal belt itself has emerged from beneath the
sea so recently and lies so nearly at sea-level that it has not been
greatly eroded, and is still covered with numerous marshes and swamps.
The rich soil and the moisture are good for rice, but the region is so
unhealthy and so hard to drain that only small parts are inhabited.
Everywhere in the coastal plain this same belted character is more
or less evident. It has much to do with all sorts of activities from
farming to politics. On consulting the map showing the cotton production
of the United States in 1914, one notices the two dark bands in the
southeast. One of them, extending from the northwestern part of South
Carolina across Georgia and Alabama, is due to the fertile soil of
the Piedmont region. The other, lying nearer the sea, begins in North
Carolina and extends well into Alabama before it swings around to the
northwest toward the area of heavy production along the Mississippi. It
is due to the fertile soil of that part of the coastal plain known
as the "cotton belt." Portions of it are called the "black belt," not
because of the colored population, but because of the darkness of the
soil. Since this land has always been prosperous, it has regularly been
conservative in politics.
The Atlantic coastal plain is by no means the only part of the United
States where the fertility of the soil is the dominant fact in the life
of the people. Because of their rich soil the prairies which extend from
western Ohio to the Missouri River and northward into Canada are fast
becoming the most steadily prosperous part of America. They owe their
surpassing richness largely to glaciation. We have already seen how the
coming of the ice-sheet benefited the regions on the borders of the old
Laurentian highland. This same benefit extended over practically the
whole of what are now the prairies. Before the advent of the ice the
whole section consisted of a broadly banded coastal plain much older
than that of the Atlantic coast. When the ice with its burden of
material scraped from the hills of the north passed over the coastal
plain, it filled the hollows with rich new soil. The icy streams that
flowed out from the glaciers were full of fine sediment, which they
deposited over enormous flood plains. During dry seasons the winds
picked up this dust and spread it out still more widely, forming the
great banks of yellow loess whose fertile soil mantles the sides of many
a valley in the Mississippi basin. Thus glaciers, streams, and winds
laid down ten, twenty, fifty, or even one hundred feet of the finest,
most fertile soil. We have already seen how much the soil was improved
by glaciation in Wisconsin and Ohio. It was in the prairie States that
this improvement reached a maximum. The soil there is not only fine
grained and free from rocks, but it consists of particles brought from
widely different sources and is therefore full of all kinds of plant
foods. In most parts of the world a fine-grained soil is formed only
after a prolonged period of weathering which leaches out many valuable
chemical elements. In the prairies, however, the soil consists largely
of materials that were mechanically ground to dust by the ice without
being exposed to the action of weathering. Thus they have reached their
present resting-places without the loss of any of their original plant
foods. When such a soil is found with a climate which is good for crops
and which is also highly stimulating to man, the combination is almost
ideal. There is some justification for those who say that the north
central portion of the United States is more fortunate than any other
part of the earth. Nowhere else, unless in western Europe, is there such
a combination of fertile soil, fine climate, easy communication, and
possibilities for manufacturing and commerce. Iron from that outlier of
the Laurentian highland which forms the peninsula of northern Michigan
can easily be brought by water almost to the center of the prairie
region. Coal in vast quantities lies directly under the surface of this
region, for the rock of the ancient coastal plain belongs to the same
Pennsylvanian series which yields most of the world's coal. Here man is,
indeed, blessed with resources and opportunities scarcely equaled in any
other part of the world, and finds the only drawbacks to be the extremes
of temperature in both winter and summer and the remoteness of the
region from the sea. Because of the richness of their heritage and
because they live safely protected from threats of foreign aggression,
the people who live in this part of the world are in danger of being
slow to feel the currents of great world movements.
The western half of the plains of North America consists of two parts
unlike either the Atlantic coastal plain or the prairies. From South
Dakota and Nebraska northward far into Canada and westward to the Rocky
Mountains there extends an ancient peneplain worn down to gentle relief
by the erosion of millions of years. It is not so level as the plains
farther east nor so low. Its western margin reaches heights of four or
five thousand feet. Here and there, especially on the western side, it
rises to the crest of a rugged escarpment where some resistant layer of
rocks still holds itself up against the forces of erosion. Elsewhere its
smooth surfaces are broken by lava-capped mesas or by ridges where some
ancient volcanic dike is so hard that it has not yet been worn away.
The soil, though excellent, is thinner and less fertile than in the
prairies. Nevertheless the population might in time become as dense and
prosperous as almost any in the world if only the rainfall were more
abundant and good supplies of coal were not quite so far away. Yet in
spite of these handicaps the northwestern peneplain with its vast
open stretches, its cattle, its wheat, and its opportunities is a most
attractive land.
South of Nebraska and Wyoming the "high plains," the last of the four
great divisions of the plains, extend as far as western Texas. These,
like the prairies, have been built up by deposits brought from other
regions. In this case, however, the deposits consist of gravel, sand,
and silt which the rivers have gradually washed out from the Rocky
Mountains. As the rivers have changed their courses from one bed to
another, layer after layer has been laid down to form a vast plain
like a gently sloping beach hundreds of miles wide. In most places the
streams are no longer building this up. Frequently they have carved
narrow valleys hundreds of feet deep in the materials which they
formerly deposited. Elsewhere, however, as in western Kansas, most of
the country is so flat that the horizon is like that of the ocean. It
seems almost incredible that at heights of four or five thousand feet
the plains can still be so wonderfully level. When the grass is green,
when the spring flowers are at their best, it would be hard to find a
picture of greater beauty. Here the buffalo wandered in the days before
the white man destroyed them. Here today is the great cattle region of
America. Here is the region where the soul of man is filled with the
feeling of infinite space.
To the student of land forms there is an ever-present contrast between
those due directly to the processes which build up the earth's surface
and those due to the erosive forces which destroy what the others have
built. In the great plains of North America two of the divisions, that
is, the Atlantic coastal plain of the southeast and the peneplain of the
northwest, owe their present form to the forces of erosion. The other
two, that is, the prairies and the high plains, still bear the impress
of the original processes of deposition and have been modified to only a
slight extent by erosion.
A similar but greater contrast separates the mountains of eastern North
America and those of the western cordillera--the fourth and last of the
main physical divisions of the continent. In both the Laurentian and
the Appalachian highlands the eastern mountains show no trace of the
original forms produced by the faulting of the crust or by volcanic
movements. All the original distinctive topography has been removed.
What we see today is the product of erosion working upon rocks that were
thousands of feet beneath the surface when they were brought to their
present positions. In the western cordillera, on the contrary, although
much of the present form of the land is due to erosion, a vast amount is
due directly to so-called "tectonic" activities such as the breaking of
the crust, the pouring out of molten lavas, and the bursting forth of
explosive eruptions.
The character of these tectonic activities has differed widely in
different parts of the cordillera. A broad upheaval of great blocks
of the earth's crust without tilting or disturbance has produced the
plateaus of Arizona and Utah. The gorges that have been rapidly cut
into such great upheaved blocks form part of the world's most striking
scenery. The Grand Canyon of the Colorado with its tremendous platforms,
mesas, and awe-inspiring cliffs could have been formed in no other way.
Equally wonderful are some of the narrow canyons in the broadly upheaved
plateaus of southern Utah where the tributaries of the Virgin and other
rivers have cut red or white chasms thousands of feet deep and so narrow
that at their bottoms perpetual twilight reigns. It is a curious proof
of the fallibility of human judgment that these great gorges are often
cited as the most striking examples of the power of erosion. Wonderful
as these gorges certainly are, the Piedmont plain or the northwestern
peneplain is far more wonderful. Those regions had their grand canyons
once upon a time, but now erosion has gone so far that it has reduced
the whole area to the level of the bottoms of the gorges. Though such
a fate is in store for all the marvelous scenery of the western
cordillera, we have it, for the present at least, as one of the most
stimulating panoramas of our American environment. No man worthy of the
name can sit on the brink of a great canyon or gaze up from the dark
depths of a gorge without a sense of awe and wonder. There, as in few
other places, Nature shows with unmistakable grandeur the marvelous
power and certainty with which her laws work out the destiny of the
universe.
In other parts of the great American cordillera some of the simplest and
youngest mountain ridges in the world are found. In southern Oregon, for
example, lava blocks have been broken and uplifted and now stand with
steep fresh faces on one side and with the old surface inclining more
gently on the other. Tilted blocks on a larger scale and much more
deeply carved by erosion are found in the lofty St. Elias Mountain of
Alaska, where much of the erosion has been done by some of the world's
greatest glaciers. The western slope of the Wasatch Mountains facing the
desert of Utah is the wall of a huge fracture, as is the eastern face
of the Sierra Nevadas facing the deserts of Nevada. Each of these great
faces has been deeply eroded. At the base, however, recent breaking and
upheaval of the crust have given rise to fresh uneroded slopes. Some
take the form of triangular facets, where a series of ridges has been
sliced across and lifted up by a great fault. Others assume the shape
of terraces which sometimes continue along the base of the mountains for
scores of miles. In places they seem like bluffs cut by an ancient lake,
but suddenly they change their altitude or pass from one drainage area
to another as no lake-formed strand could possibly do.
In other parts of the cordillera, mountains have been formed by a single
arching of the crust without any breaking. Such is the case in the Uinta
Mountains of northwestern Utah and in some of the ranges of the Rocky
Mountains in Colorado. The Black Hills of South Dakota, although lying
out in the plains, are an example of the same kind of structure and
really belong to the cordillera. In them the layers of the earth's crust
have been bent up in the form of a great dome. The dome structure, to be
sure, has now been largely destroyed, for erosion has long been active.
The result is that the harder strata form a series of concentric ridges,
while between them are ring-shaped valleys, one of which is so level and
unbroken that it is known to the Indians as the "race-course." In
other parts of the cordillera great masses of rock have been pushed
horizontally upon the tops of others. In Montana, for example, the
strata of the plains have been bent down and overridden by those of
the mountains. These are only a few of the countless forms of breaking,
faulting, and crumpling which have given to the cordillera an almost
infinite variety of scenery.
The work of mountain building is still active in the western cordillera,
as is evident from such an event as the San Francisco earthquake. In the
Owens Valley region in southern California the gravelly beaches of old
lakes are rent by fissures made within a few years by earthquakes. In
other places fresh terraces on the sides of the valley mark the lines of
recent earth movements, while newly formed lakes lie in troughs at
their base. These Owens Valley movements of the crust are parts of the
stupendous uplift which has raised the Sierra Nevada to heights of over
14,000 feet a few miles to the west. Along the fault line at the base
of the mountains there runs for over 9.50 miles the world's longest
aqueduct, which was built to relieve Los Angeles from the danger of
drought. It is a strange irony of fate that so delicate and so vital
an artery of civilization should be forced to lie where a renewal of
earthquake movements may break it at any time. Yet there was no other
place to put it, for in spite of man's growing control of nature he
was forced to follow the topography of the region in which he lived and
labored.
On the southern side of the Mohave Desert a little to the east of where
the Los Angeles aqueduct crosses the mountains in its southward course,
the record of an earthquake is preserved in unique fashion. The steep
face of a terrace is covered with trees forty or fifty years old. Near
the base the trees are bent in peculiar fashion. Their lower portions
stand at right angles to the steeply sloping face of the terrace, but
after a few feet the trunks bend upward and stand vertically. Clearly
when these trees were young the terrace was not there. Then an
earthquake came. One block of the earth's crust was dropped down while
another was raised up. Along the dividing line a terrace was formed. The
trees that happened to stand along the line were tilted and left in a
slanting position on the sloping surface between the two parts of the
earth's crust. They saw no reason to stop growing, but, turning their
tips toward the sky, they bravely pushed upward. Thus they preserve in a
striking way the record of this recent movement of the earth's crust.
Volcanoes as well as earth movements have occurred on a grand scale
within a few hundred years in the cordillera. Even where there is today
no visible volcanic activity, recent eruptions have left traces as
fresh as if they had occurred but yesterday. On the borders of the Grand
Canyon of the Colorado one can see not only fresh cones of volcanic
ash but lava which has poured over the edges of the cliffs and hardened
while in the act of flowing. From Orizaba and Popocatepetl in Mexico
through Mount San Francisco in Arizona, Lassen Peak and Mount Shasta
in California, Mount Rainier with its glaciers in the Cascade Range of
Washington, and Mount Wrangell in Alaska, the cordillera contains an
almost unbroken chain of great volcanoes. All are either active at
present or have been active within very recent times. In 1912 Mount
Katmai, near the northwestern end of the volcanic chain, erupted so
violently that it sent dust around the whole world. The presence of the
dust caused brilliant sunsets second only to those due to Krakatoa
in 1883. It also cut off so much sunlight that the effect was felt in
measurements made by the Smithsonian Institution in the French provinces
of North Africa. In earlier times, throughout the length of the
cordillera great masses of volcanic material were poured out to form
high plateaus like those of southern Mexico or of the Columbia River in
Oregon. In Utah some of these have been lifted up so that heavy caps of
lava now form isolated sheets topping lofty plateaus. There the lowland
shepherds drive their sheep in summer and live in absolute isolation for
months at a time. There, as everywhere, the cordillera bears the marks
of mountains in the making, while the mountains of eastern America bear
the marks of those that were made when the world was young.
The geysers and hot springs of the Yellowstone are another proof of
recent volcanic activity. They owe their existence to hot rocks which
lie only a little way below the surface and which not long ago were
molten lava. The terraces and platforms built by the geysers are another
evidence that the cordillera is a region where the surface of the earth
is still being shaped into new forms by forces acting from within. The
physical features of the country are still in process of construction.
In spite of the importance of the constructive forces which are still
building up the mountains, much of the finest scenery of the cordillera
is due to the destructive forces of erosion. The majestic Columbia
Canyon, like others of its kind, is the work of running water. Glaciers
also have done their part. During the glacial period the forces which
control the paths of storms did not give to the cordillera region such
an abundance of snow as was sifted down upon Laurentia. Therefore no
such huge continental glaciers have flowed out over millions of square
miles of lower country. Nevertheless among the mountains themselves the
ice gouged and scraped and smoothed and at its lower edges deposited
great moraines. Its work today makes the cliffs and falls of the
Yosemite one of the world's most famous bits of scenery. This scenery
is young and its beauty will pass in a short time as geology counts the
years, for in natural scenery as in human life it is youth that makes
beauty. The canyons, waterfalls, and geysers of the cordillera share
their youth with the lakes, waterfalls, and rapids due to recent
glaciation in the east. Nevertheless, though youth is the condition of
most striking beauty, maturity and old age are the condition of greatest
usefulness. The young cordillera with its mountains still in the making
can support only a scanty population, whereas the old eastern mountains,
with the lines of long life engraved upon every feature, open their arms
to man and let him live and prosper.
It is not enough that we should picture merely the four divisions of the
land of our continent. We must see how the land meets the sea. In low
latitudes in both the Old World and the New, the continents have tended
to emerge farther and farther from the sea during recent geological
times. Hence on the eastern side of both North and South America from
New Jersey to Brazil the ocean is bordered for the most part by coastal
plains, uplifted from the sea only a short time ago. On the mountainous
western side of both continents, however, the sea bottom shelves
downward so steeply that its emergence does not give rise to a plain
but merely to a steep slope on which lie a series of old beaches several
hundred and even one thousand feet above the present shore line. Such
conditions are not favorable to human progress. The coastal plains
produced by uplift of the land may be fertile and may furnish happy
homes for man, but they do not permit ready access to the sea because
they have no harbors. The chief harbor of Mexico at Vera Cruz is merely
a little nick in the coast-line and could never protect a great fleet,
even with the help of its breakwater. Where an enterprising city like
Los Angeles lies on the uplifted Pacific coast, it must spend millions
in wresting a harbor from the very jaws of the sea.
In high latitudes in all parts of the world the land has recently been
submerged beneath the sea. In some places, especially those like the
coasts of Virginia and central California which lie in middle latitudes,
a recent slight submergence has succeeded a previous large emergence.
Wherever such sinking of the land has taken place, it has given rise to
countless bays, gulfs, capes, islands, and fiords. The ocean water has
entered the valleys and has drowned their lower parts. It has surrounded
the bases of hills and left them as islands; it has covered low valleys
and has created long sounds where traffic may pass with safety even in
great storms. Though much land has thus been lost which would be good
for agriculture, commerce has been wonderfully stimulated. Through Long
Island Sound there pass each day hundreds of boats which again and again
would suffer distress and loss if they were not protected from the open
sea. It is no accident that of the eight largest metropolitan districts
in the United States five have grown up on the shores of deep inlets
which are due to the drowning of valleys.
Nor must the value of scenery be forgotten in a survey such as this.
Year by year we are learning that in this restless, strenuous American
life of ours vacations are essential. We are learning, too, that the
love of beauty is one of Nature's greatest healers. Regions like the
coast of Maine and Puget Sound, where rugged land and life-giving ocean
interlock, are worth untold millions because of their inspiring beauty.
It is indeed marvelous that in the latitude of the northern United
States and southern Canada so many circumstances favorable to human
happiness are combined. Fertile soil, level plains, easy passage across
the mountains, coal, iron, and other metals imbedded in the rocks, and
a stimulating climate, all shower their blessings upon man. And with all
these blessings goes the advantage of a coast which welcomes the mariner
and brings the stimulus of foreign lands, while at the same time it
affords rest and inspiration to the toilers here at home.