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ture; and of all mountains, those of the torrid zone are the best adapted for this purpose. The celebrated traveler and naturalist, Humboldt, has the following remarks on this subject:

16. "Among the colossal mountains of Quito and Peru, furrowed by deep ravines, man is enabled to contemplate alike all the families of plants, and all the stars of the firmament. There, at a single glance, the eye sur veys majestic palms, humid forests of bambusa, and the varied species of musacea; while above these forms of tropical vegetation appear oaks, medlars, the sweet-brier, and umbelliferous plants, as in our European homes. There, as the traveler turns his eyes to the vault of heaven, a single glance embraces the constellation of the Southern Cross, the Magellanic clouds, and the guiding stars of the constellation of the Bear, as they circle round the arctic pole. There the depths of the earth and the vaults of heaven display all the richness of their forms and the variety of their phenomena. There the different climates are ranged the one above the other, stage by stage, like the vegetable zones, whose succession they limit; and there the ob server may readily trace the laws that regulate the diminution of heat, as they stand indelibly inscribed on the rocky walls and abrupt declivities of the Cordilleras."

17. Let these remarks suggest to the reader how much of interest the various aspects of nature present to the observant eye of the philosopher, and how much a knowledge of the laws of nature is calculated to contribute to our intellectual pleasures.

LESSON VI.—TABLE-LANDS, PLAINS, AND VALLEYS.

1. THE earth's surface exhibits great variety in aspect, forming mountains, hills, table-lands, plains, and valleys. The most general of these features are what geographers term table-lands or plateaus, and lowlands or plains.

2. In considering the climate, and, consequently, the products of a country, it is necessary to observe its altitude above the ocean level, as well as its distance from the equator. A difference of 350 feet vertically is equal to a difference of 60 miles horizontally in a direction north and south. The mean temperature of a place at an elevation of 350 feet corresponds to the mean temperature of a location 60 miles farther north and on the sea-level. In tropical regions the elevated tablelands have frequently a rich soil and the most genial climate, affording to man a delightful and picturesque abode.

3. Unquestionably the most extensive plateau in the world is the lofty table-land of Central Asia, which is from five thousand to fifteen thousand feet high. Bounded and inter

sected by lofty mountain ranges, having the great Altaian chain on the north, and the Himalayas and Mountains of China on the south and east, it is without a single opening to the sea, and its water system consists of lakes without outlets, the final recipients of many rivers. The largest of these inland lakes or seas are the Caspian and the Aral, in both of which the waters are salt, though less so than those of the

ocean.

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4. While the Eastern continent is remarkable for its tablelands, ours is the land of plains, which form two thirds of the surface of the Western world. South America, with the exception of the long, narrow table-land of the Andes, may considered one vast plain, divided into three principal portions—the llanos, or low grassy plains of the Orinoco and its tributaries; the selvas, or forest plains, which make the great basin of the Amazon; and the pampas, or level plains of the La Plata. In the wet season the grassy plains of South America are covered with the most luxuriant vegetation, but in the, dry months they present the appearance of a wide waste of desolation.

5. North America has its plateau, which extends along the eastern side of the Rocky Mountains, and includes the tablelands of Utah and Mexico; but the most remarkable feature in its physical conformation is its vast central plain, the largest, not of America only, but of the world. It embraces the basin of the Mississippi and its tributaries, together with the basins of the St. Lawrence and the great lakes, and, stretching away far to the north, it approaches the borders of the Frozen Sea. Nearly all of its northern portion, north of the fiftieth degree of latitude, is a bleak and barren waste, occupied by numerous lakes, and bearing a striking resemblance to northern Asia; but its more southern portion, "the Valley of the Mississippi," not only enjoys a happy climate, but is one of the most fertile regions in the world, capable of sustaining an immense population, and doubtless destined to be the seat of a vast empire. "Who does not see," says Guyot,

"that here is the character of America-that here lies the future of the New World; while the countries of mountains and plateaus seem destined to play only a secondary part ?"

6. The accompanying chart of a large portion of North America will give a very correct idea of the physical configuration of the country, showing the comparative elevations of its different parts above the ocean level. Yet the elevations on this chart are 120 times enlarged beyond their true

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insignificant when we compare them with the size of the great itself is drawn, showing that the loftiest mountains are quite relative height as compared with the scale on which the map

globe itself.

called prairies, a word signifying meadows. These natural leys of the Missouri and Mississippi, and also in Texas, are 7. Portions of the great North American plain, in the val

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meadow-lands, covered chiefly with grass, and presenting, in the summer season, the grandest display of floral vegetation which the sun looks down upon, are grouped in three divisions, as bushy prairies, wet or swampy prairies, and rolling prairies. It is the latter, more particularly, which are described in the following lesson as the "gardens of the desert" "island groves hedged round with forests."

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THESE are the gardens of the desert, these
The unshorn fields, boundless and beautiful,
For which the speech of England has no name-
The prairies. I behold them for the first,
And my heart swells, while the dilated sight

Takes in the encircling vastness. Lo! they stretch
In airy undulations far away,

As if the ocean, in his gentlest swell,

Stood still, with all his rounded billows fixed,
And motionless forever. Motionless?

No-they are all unchained again. The clouds
Sweep over with their shadows, and, beneath,
The surface rolls and fluctuates to the eye;
Dark hollows seem to glide along and chase
The sunny ridges. Breezes of the south!

Who toss the golden and the flame-like flowers,
And pass the prairie-hawk that, poised on high,

Flaps his broad wings, yet moves not-ye have played
Among the palms of Mexico and vines

Of Texas, and have crisped the limpid brooks
That from the fountains of Sonora glide

Into the calm Pacific-have ye fanned

A nobler or a lovelier scene than this?

Man hath no part in all this glorious work:

The hand that built the firmament hath heaved

And smoothed these verdant swells, and sown their slopes

With herbage, planted them with island groves,

And hedged them round with forests. Fitting floor

For this magnificent temple of the sky

With flowers whose glory and whose multitude

Rival the constellations! The great heavens
Seem to stoop down upon the scene in love-
A nearer vault, and of a tenderer blue,
Than that which bends above the eastern hills.
As o'er the verdant waste I guide my steed,
Among the high, rank grass that sweeps his sides,
The hollow beating of his footstep seems

A sacrilegious sound. I think of those
Upon whose rest he tramples. Are they here-
The dead of other days?-and did the dust
Of these fair solitudes once stir with life

And burn with passion? Let the mighty mounds
That overlook the rivers, or that rise

In the dim forest, crowded with old oaks,
Answer. A race that long has passed away
Built them; a disciplined and populous race

Heaped, with long toil, the earth, while yet the Greek
Was hewing the Pentelicus to forms

Of symmetry, and rearing on its rock

The glittering Parthenon. These ample fields
Nourished their harvests; here their herds were fed,
When haply by their stalls the bison lowed,

And bowed his manéd shoulder to the yoke.

All day this desert murmured with their toils,

Till twilight blushed, and lovers walked and wooed
In a forgotten language, and old tunes,
From instruments of unremembered form,
Gave the soft winds a voice.-BRYANT.

LESSON VIII.-CAVES AND GROTTOES OF THE OLD WORLD.

1. NATURAL caves, which are hollow places under ground, generally with openings on the surface, form a division of physical geography interesting alike to the man of science and the mere wonder-loving tourist. Nearly all the great caves in the world are in limestone rocks, and have been produced by the action of water, which, running in little streams through the strata and dissolving particles of rock,* has, in the course of ages, formed subterranean passages, often of great extent and wonderful beauty. Caves found in rocks of granite, lava, and porphyry, owe their origin to other

causes.

2. It is not surprising that the priests of antiquity, for the purpose of producing an effect on the minds of the ignorant populace, localized their false divinities in caverns, which were so well calculated to awaken curiosity and excite the imagination. Thus the original Delphian oracles, reverenced by

* The water carries with it carbonic acid gas, by which limestone is rendered soluble.

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