DISTRIBUTION OF THE LAND-AREAS. 37

 

The materials thus carried away are

rocks.
spread over the lowlands near the mouth of the
river or thrown into the sea, where they often

form large deposits. By the constant action of
these causes the mean heights of the continents are
decreasing and their breadths increasing.

The most remarkable instance of erosion is

found in the cafions of the Colorado River, where.

the waters have eaten a channel through the hard
limestones and granites that form the bed of the
stream, until they now run through gorges whose
walls ascend almost perpendicularly to the height
of from 3000 to 6000 feet.

A good idea of this great depth may be obtained by
walking along a straight street for about a mile (5280
feet), and then imagining the street set upright in the air.
On looking down toward the starting-place, we would see
it as it would appear at the bottom of a hole about 6000
feet deep.’ ;

The forms produced by erosion are often extremely fan-
tastic. Tall, slender, needle-like columns, capped by a
layer of harder rock, sometimes occur, thus showing in a
marked manner an effect of erosion.

(4.) By the Action of Ocean Waves, changing
the outlines of coasts; as may be seen in portions
of the coasts of England and Scotland.

(5.) By the Agency of Man, witnessed mainly
in the destruction of the forests over extended
areas.

(6.) By the Contraction of a Cooling Crust,
resulting in—1. Earthquakes; 2. Volcanoes; 3.
Gradual uplifts and subsidences.

2020300

CHAPTER II.
Distribution of the Land-Areas.

80. Geographic Effects of Light, Heat, and
Moisture.—The peculiarities observed in the dis-
tribution of animal and vegetable life are caused
by differences in the distribution of light, heat,
and moisture. Since light, heat, and moisture
* are influenced by the interaction of land, water,
and air, we must first study the distribution and
grouping of these inorganic or dead forms before
we can understand those that are living.

81. The Distribution of the Land—Of the
197,000,000 square miles that make up the
darth’s surface, about 144,000,000 are water and
53,000,000 land. The proportion is about as the
square of 5 is to the square of 8. If, therefore,
we erect a square on a side of five, its entire area
will represent the relative water-area of the globe;

 

 

 

while a square whose side is three will represent
the relative land-area.

 

 

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82. The Distribution of the Land can be best
studied when arranged under two heads:

(1.) The Horizontal Forms of the Land, or the
different shapes produced in the land-areas by the
coast lines, or by the contact of land and water;

(2.) The Vertical Forms of the Land, produced
by the irregularity of the surface of the high
lands and low lands.

83. The Horizontal Forms.—The land-areas
are divided into continents and islands.

The Eastern Hemisphere contains four conti-

       
    
  

 

 

‘nents: Europe, Asia, Africa, and Australia. The

first three form one single mass, which is called
the Eastern Continent.

Though the word “continent” strictly refers to an ex-
tended area of land entirely surrounded by water, usage
has sanctioned the application of the term to the grand
divisions of the land. It is quite correct, therefore, to
speak of the North American Continent, the Asiatic Con-
tinent, ete.

The Western Hemisphere contains two conti-
nents: North and South America; these consti-
tute what is called the Western Continent.

The following are the extremities of the conti:
nents:

In the Hastern Continent—

Most northern point, Cape Chelyuskin, lat. 78° 16’ N.
Most southern point, Cape Agulhas, lat. 34°51’ 8.

Most eastern point, East Cape, long. 170° W.

Most western point, Cape Verd, long. 17° 34’ W.

In the Western Continent—

Most northern point, Point Barrow, lat. 72° N.

Most southern point, Cape Froward, lat. 53° 53’ 8.

Most western point, Cape Prince of Wales, long. 168° W.
Most eastern point, Cape St. Roque, long. 35° W.

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