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there are other circumstances which modify or change the climate of particular places. Islands and coasts feel the influence of the sea air, which is not only moist, but is neither very

hot very cold : it therefore softens the severity of winter, and abates the heat of summer. Consequently, places exposed to its influence are rendered more temperate.

Great accumulations of ice and snow materially affect climate. The great masses of snow and ice in the regions of Greenland impart their chilling influence to the winds, which visit us from the north, and constitute one of the causes of the greater coldness of our climate, than that of other countries in the same latitude. These cold winds, mingled with the sea breezes, which come from the Atlantic, give that harsh and chilling quality so remarkable in the easterly winds of New England.

Mountains which shelter a country from cold winds, render the climate warmer. In all parts of our country, the southern declivities of mountains, and places lying south of them, sheltered from the north winds, are well known to be much warmer. So great is the difference observed in such places, that in some cases plants, which would flourish on the southern side of a mountain, would perish on the northern.

Elevation above the level of the sea is an important circumstance in climate. The city of Mexico, which according to its latitude should be excessively hot, being elevated 7000 feet above the level of the sea, enjoys a climate of perpetual spring Quito, which lies under the equator, has a similar climate. Within sight of this city, at an elevation of 15 or 16,000 feet, the tops of the mountains are so cold as to be covered with never changing masses of snow and ice. At the distance of a few miles, the inhabitants of Guayaquil, living on a low and level margin of the sea, experience an intense and sickly degree of heat.

Thus we have illustrated, in referring to the climate of America, most of the causes which form or modify climate generally. It may be here added, that man exercises a slow but powerful influence upon the climate of those countries, which become the subjects of his labor. By the levelling of forests and the draining of marshes, the sun is let in upon the soil, and the climate is rendered warmer, drier, and more salubrious. Such is the powerful influence of this cause alone, that our own winters are much shorter, the quantity of snow that falls is considerably smaller, and the cold far less intense than when our forefathers first settled the country. Some parts of the western country, in the United States, once esteemed exceedingly unhealthy, since the clearing up of the forests, have become remarkable for salubrity.

The climate of Europe is affected by various circumstances, rendering some parts more temperate, and others colder or warmer than might be expected from their latitude. The eastern portion of Europe, including two thirds of Russia in Europe, is rendered colder by the winds which sweep over it, chilled by the immense masses of snow and ice embosomed in the mountains of central Asia. The southern parts of Europe are rendered warmer by the hot winds which visit them from the burning deserts and plains of Africa. The extremes both of heat and cold are diminished in those countries which berder upon the Atlantic, by the constant action of the sea air. These appear to be the three great causes, which modify the climate of Europe, and render it so different in some parts, from what it is in others of the same latitude ; and so different from the climate of those portions of America, which lie in the same parallels.

There is another fact to be taken into consideration, in comparing the climate of the Atlantic part of Europe with that of the Atlantic part of North America. In Greenland, and the adjacent regions, there are immense masses of snow and ice, which accumulate from year to year, or are broken up, in the form of icebergs, sometimes reaching the tropics before they are melted. On the contrary, on the borders of Europe, such accumulations do not take place. The gulfs of Norway are almost always open, while the coast of Greenland, exactly opposite, is frequently rendered inaccessible, from fixed or floating barriers of ice.

These considerations will be sufficient to account for most of the contrasts, which we observe between our own climate, and that of the Atlantic parts of Europe. The climate of England, being surrounded by the sea, is rendered by the sea air much more temperate. The winters in that country are less extreme, than those of the southern parts of New England. Newfoundland, although surrounded by the sea, and further south than England, swept by the winds, which come from the icy regions of the north and the adjacent countries, experiences a winter so intense as almost to render it uninhabitable. Spain, Italy, and Turkey in Europe, illustrate the influence of the warm winds of Africa. Situated in the latitude of Niassachusetts and New York, they produce oranges, lemons, figs, and grapes, which in our country are the products of-regions at least 12 degrees further south. The difference of the climate between the eastern and western parts of Europe in the same latitude, is shown by the fact, that at Moscow, which is in the latitude of Edinburgh, the winter is so inclement, as to render every precaution necessary to guard against it, while at the latter place it is not more severe than at Boston.

4. Seasons of the Torrid Zone. There are only two seasons in the torrid zone ; the dry and the rainy or wet. The latter prevails in the tropical regions over which the sun is vertical, and is succeeded by the dry season, when the sun retires to the other side of the equator. The rains are produced by the powerful action of a vertical sun, rapidly accumulating vapors by evaporation, which then descend in rains ; this arrangement is wisely adapted to afford a shelter from the perpendicular rays of the sun. In some regions there are two rainy seasons, one of which is much shorter than the other. Nothing equals the majestic beauty of the summer in the torrid zone. The sun rises vertically ; it traverses rapidly the red clouds of the east, and fills the heavens with a light, whose brightness is unobscured by a single shade. The moon shines here with a more brilliant lustre. Venus blazes with purer and more vivid rays, and the milky way glitters with augmented brightness. To all this we may add the serenity of the air, the luxuriance of vegetation, and the gigantic forms of plants and animals ; all nature more grand and more animated, at the same time, that the seasons are more constant and unvarying.

5. Seasons of the Temperate Zones. The four seasons which we distinguish in this country, are known only in the temperate zones, which alone are blessed with the varied charms of spring and autumn, the tempered heats of summer, and the salutary rigors of winter. In the part of the temperate zone bordering on the tropics, the climate resembles that of the intertropical regions ; and it is between 40° and 60° of latitude, that the succession of seasons is most regular and perceptible.

6. Seasons of the Frigid Zones. Beyond the 60th degree of latitude only two seasons take place; a long and severe winter is there suddenly succeeded by insupportable heats. The rays of the sun, notwithstanding the obliquity of their direction, produce powerful effects, because the great length of the days favors the accumulation of heat ; in three days the snow is dissolved, and flowers at once begin to blow.

7. Winds. Wind is a current of air moving in some particular direction ; the velocity and force of winds are various. The following table shows the degrees of velocity of different winds. Velocity. — 4 or 5 miles an hour. Name of the Wind. — Gentle wind, 10 to 15

Brisk Gale, 30 to 35

High wind, 50

Storm, 80 to 100

Hurricane. The utility of winds is very great ; they purify the atmosphere, and dissipate the miasmata exhaled from marshes and stagnant waters. They raise and transport the clouds destined to fertilize the earth. Millions of seeds, furnished with little pinions, are scattered by them far and wide, thus extending the empire of vegetation. They propel a vast deal of machinery, and transport ships from pole to pole on the great highway of nations.

8. Permanent, Periodical, and Variable winds. Winds may be divided into three classes ; permanent winds, or those which blow constantly in the same direction ; periodical winds, or those which blow in one direction only a certain part of the year, and variable winds, which are constantly changing their direction.

9. Trade-winds. The permanent winds blowing constantly between, and a few degrees beyond the tropics, from east to west, are called trade-winds. They prevail in the Pacific, Atlantic, and parts of the Indian ocean, to about 30° each side of the equator, being on the north a little from the northeast, and on the south from the southeast. In sailing, therefore, from the Canaries to Cumana, or from Acapulco to the Philippines, the winds blow so steadily, that it is hardly necessary to touch the sails.

10. Monsoons. In the Indian ocean to the north of 10° S., and in the seas around Malaysia, there prevail periodical winds called monsoons, which blow half the year from one quarter, and the other hall from the opposite direction ; at the time of their shifting or breaking up, variable winds and violent storms prevail. On the north of the equator a southwest monsoon olows from April to October, and during the rest of the year a northeast monsoon ; on the south of the equator a southeast wind prevails from April to October, and a northwest wind the other half of the year.

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11. Land and Sea Breezes. There is another kind of periodical winds, common on islands and coasts in tropical countries. During the day, when the air over the land is heated by the sun, a cool breeze sets in from the sea ; this blows from about 10 A. M. to 6 P. M. At night, on the contrary, a land-breeze prevails, that is, the wind sets off from the land till about 8 A. M., when it dies away. 12. Hurricanes, Whirlwinds, Waterspouts, &c. Hurricanes are violent storms of wind,

blowing with great fury, often from opposite points of the compass, and causing dreadful devastations. They are rare beyond the tropics. Whirlwinds are sometimes caused by two winds meeting, each from different directions, and then turning rapidly round upon a centre ; and sometimes by the form of mountains, which occasions gusts of wind to descend with a spiral or whirling motion. Waterspouts which are met with at sea, and are dangerous to ships, have been supposed to be formed by the raising up of water from the sea by whirl

winds. This opinion, however, Waterspout.

seems to be doubtful ; for accord

ing to some observers, the water discharged on the bursting of a waterspout is always fresh, and

therefore must have passed into the air in the form of vapor. The simoom of the desert of Sahara, the samiel of the Arabian deserts, the chamseen of Egypt, and the harmattan of Guinea, the solano of Spain, the sirocco of Italy, and the northwest wind of New South Wales, are noxious, hot winds, some of which merely produce languor, while others, if admitted into the lungs, cause suffocation.

13. Clouds. Every part of the land and water is constantly imparting to the atmosphere portions of its substance, in the form of vapor. This is condensed by cold, and formed into mists and clouds. In ascending to the summits of high mountains, the traveller sometimes passes through a zone of clouds, and beholds the extensive vapors of which it is composed stretched under his feet, like a vast plain covered with snow. He will, however, discover other clouds far above the tops of the loftiest peaks. There is no part of nature which more adorns the universe than the clouds. The beauty of their various tints, the variety of their forms, the sublimity of their masses, the grandeur of their movements, are all calculated to affect the imagination, and direct the attention to their great Author.

The utility of the clouds is no less obvious than their beauty. They scatter over the land the dew, rain, snow, and hail ; all of which contribute to refresh and fertilize the earth. We observe all nature to languish, when the clouds retain their stores too long ; plants fade and droop ; animals feel their strength failing them; man himself, breathing nothing but dust, can with difficulty procure shelter from the sultry heat, by which his frame is parched and overpowered. No sooner has the water fallen from the clouds, than all living things begin to revive, the fields resume their green attire, the flowers their lively tints, animals the sportive freedom of their motions, and the elements of the air their healthful equilibrium.

The association of certain forms of clouds with the state of the weather has long been observed, and meteorologists have divided them into seven species : 1 The cirrus, resembling a lock of hair or a feather ; it is high and indicates a breeze ; 2. The cumulus, a dense cloud nearer the earth, the prognostic of settled weather ; 3. The stratus, a low, continuous, level sheet of cloud, indicative of serene weather ; 4. The cirro-cumulus consists of dense rounded masses, at different heights, also a sign of fine weather ; 5. The cirro-stratus is long and narrow, but changeable, often high, but descends to the earth as a soaking dense mist; when stationary it indicates rain or snow ; 6. The cumulo-stratus, in which the cumulus is mixed with the cirro-stratus or cirro-cumulus ; the thunder-cloud is of this species ; 7. The nimbus is a shower seen in profile ; the thunder-cloud, on discharging its electricity, generally passes into the nimbus.

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14. Mirage. The mirage, or appearance of objects which are not actually in the horizon, or which exist there in a different situation, is one of the most remarkable of optical illusions. At sea, rocks and sands concealed under the water, appear as if they were raised above the surface. The Swedish sailors long searched for a pretended magic island, which from time to time could be descried between the isle of Aland and the coast of Upland. It proved to be a rock, the image of which was presented in the air by

the mirage. At one time the Fata Morgana.

English saw with terror the coast

of Calais and Bologne, in France, apparently approaching the shores of their island. But the most celebrated example of mirage is frequently exhibited in the straits of Messina. The inhabitants, standing on the Italian side, perceive images of palaces, embattled ramparts, houses, and ships, and all the varied objects of towns and landscapes, in the air. This appearance is regarded by the people as the work of fairies, and is called Fata Morgana.

15. Aurora Borealis. This phenomenon is commonly called the northern lights ; it is frequently to be seen in New England, and generally in the north. It usually commences two or three hours after sunset, and consists of a whitish light, sometimes appearing and disappearing, and occasionally flashing nearly up to the zenith. Previous to the war of the Revolution, these lights assumed a reddish hue, and were imagined to represent, in their bloody outlines, the marching of armies and the turmoil of battle. In more northern regions they offer a more brilliant display than in our country. Various explanations are given of these remarkable phenomena ; but

there is no established theory on the subject. Aurora Borealis, in Lapland.

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VII. STRUCTURE OF THE EARTH. MINERALS.

1. Arrangement of the Materials. Persons unaccustomed to examine the structure of the crust of the earth, are apt to imagine that mineral masses present a confused heap of matter, without any particular order or arrangement. But wherever water-courses, artificial excavations, or precipices, expose the structure, we find striking proofs of the agency of causes that must have acted with great uniformity over vast portions of the surface, and that have produced a general resemblance between the structure of widely distant countries. Much of the materials is arranged in beds, of different extent and thickness, but indicating the operation of one common agent.

Such beds are termed strata, and the general fact is expressed by the term stratification. These strata sometimes consist of loose or slightly consolidated masses of clay or sand, and sometimes of hard, stony bodies, which are easily split in the direction of the strata. The schists or slates are an example. Wherever natural or artificial sections lay open the earth's crust to a sufficient depth, we generally find the strata resting on a different kind of rock, which has no marks of a stratified structure. Hence the distribution of rocks into two great divisions, the stratified and the unstratified ; examples of the latter are granite, quartz, &c. All of the unstratified and some of the stratified rocks have a granular or crystaline structure, which indicate that they have formerly been melted by the action of fire ; while the regular

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distribution into layers or strata, shows that the masses so arranged have been formed by aquepus deposits, or the gradual throwing down of earthy particles from water. When the stratified rocks are crystaline, we are led to infer that they have been, at least partially, melted by fire, since they were deposited by the waters in their existing order. All these processes may still be seen going on at the mouths of rivers, around springs, and in volcanic regions, but on a smaller scale than in former ages of the world.

2. Organic Remains. Almost all the stratified rocks contain the remains of organic beings, animal or vegetable, or both, and it is in these relics of the past, that the geologist reads some portions, at least, of the former history of the earth, in periods long anterior to tradition, or even the existence of man on this globe. Plants, shells, and corallines, were first noticed as entering into the composition of rocks, and next the remains of fishes and of other vertebrated animals, were distinctly recog

nised. These relics are someSkeleton of Megatherium. Skeleton of Fossil Elk.

times of marine and sometimes of
fresh-water origin, and sometimes
are the productions of the land.
The rocks, in which they are
contained, and which are now
often at great depths beneath the
surface, — covered by
merous series of strata, several
thousand feet in thickness,
once formed the surface of the
earth's crust; the lower rocks in
the series will generally be found
to contain marine remains ; the
stratum above will, perhaps, con-
tain fresh-water shells ; above this
we shall perhaps find plants or the
remains of huge saurians or lizards,

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indicating vast swamps or marshes; Plesiosaurus, Ichthyosaurus, Pterodactylus, Fossil Plants, &c. higher up we shall meet with quad

rupeds which occupied dry land ; in this way we may show that the spot in which these discoveries are made, has been successively the bottom of the sea, the bottom of a lake or river, a marsh or swamp, high and dry land. Sometimes these remains alternate with each other, so that, for instance, the layers will present marine remains, then fresh water, then marine again, then land, then marine or fresh water, and so on; proving that the surface has been sometimes raised and sometimes depressed, so as to emerge from the

ocean, become the habitation of Fossil Tapir, Lophiodon, Dog, Crocodile, &c.

other creatures, and again be sub

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