valleys, lakes disappear, and rocks and islands rear their wet summits from the bosom of the foaming sea.

6. Valleys. The spaces which separate one mountain from another, or one chain from another, are called valleys, and their lowest part is generally the bed of a river, which rises in the higher grounds, or of a lake. The term valley is also applied in a wider sense to the whole extent of country drained by a river and its branches.

7. Plains. The surface of the earth seldom forms a perfect level for any great extent; it has a more or less perceptible inclination, generally rising from the coasts towards the interior, and even those regions which are described as plains, have an undulating surface. In some instances there are extensive plains of great elevation, called plateaux or table-lands, the descent from which to the low countries, exhibits to the inhabitants of the latter the appearance of a long chain of mountains.

8. Deserts, Steppes, &c. There are vast tracts consisting merely of wide plains of sand or shingle, or occasionally broken only by bare rocky heights, destitute of water and vegetation, and shunned equally by man and beast; these are called deserts. Interspersed over these oceans of sand, we sometimes find fertile spots, watered by springs and covered with trees, called oases. In some places we meet with vast plains entirely destitute of trees, but bearing grasses, saline and succulent plants, and dwarfish shrubs. Those which bear nutritive herbage are called prairies, llanos, or pampas; while those which have a scanty, and often only a temporary vegetation, are called steppes or karroos.

1. Lakes. An inland body of water not immediately connected with the ocean or any of its branches, is called a lake; but some bodies of this description are also commonly called seas. They are generally fresh, but are salt when situated in districts of which the soil contains saline matter.

2. Classes of Lakes. There are four sorts of lakes. (1.) The first class includes those which have no outlet and receive no running water; these are usually very small.

(2.) The second class comprises those which have an outlet, but which do not receive any running water. They are generally in elevated situations, and are often the sources of large rivers; they are formed by springs rising up into a large hollow, until the water runs out over the lowest part of the edge of the basin.

(3.) The third class embraces those lakes which receive and discharge streams of water, and is the most numerous. These lakes are the receptacles of the waters of the neighboring country, but in general have but one outlet which bears the name of the principal river that enters the lake. Such a river is said to traverse or flow through the lake, though not with strict propriety, since its current is commonly lost in the general mass of waters, and the outlet is in fact a newly formed river. The largest lakes of this class are the great lakes which lie on the northern frontier of the United States, and of which the St. Lawrence is the only outlet o the sea.

(4.) The fourth class of lakes includes those which receive without discharging rivers. The largest of these is the Caspian Sea, which swallows up several large rivers; Lake Aral also belongs to this class. They are both salt, and this is the case with most of those which have no outlet.

The following table exhibits the dimensions of the principal lakes.

3. Periodical Lakes. In tropical countries the violence of the rains often forms temporary lakes, covering spaces of several hundred miles in extent. South America has large lakes which are annually formed during the rainy season, and are therefore called periodical lakes, they are again dried up by the heats of a vertical sun.

4. Lagoons. The waters of one river or several rivers, before reaching the sea, sometimes spread out over a large surface, filling a shallow basin, which communicates with the ocean by a narrow channel. The eastern shore of the Southern States, and the coasts of the Gulf of Mexico present a great number of these basins, described under the various names of sounds, lakes, and bays; they may be more properly and conveniently denominated lagoons.

5. Springs. Springs are small reservoirs, which receive their waters from the neighboring ground through small channels, and which are usually discharged by overflowing. The origin of springs must be referred to various causes; among these the most common are the falling of rain and dew, and the melting of ice and snow. Mountains attract the fogs and clouds which float around them; consequently more rain and snow fall upon them than upon the plains. The waters descend, forming innumerable streams, some in the shape of rivers, and others in the form of springs.

Spouting springs are formed by having their source considerably elevated above the aperture at which they issue. They are constructed on the same principles as artificial fountains, — the column of water being thrown upwards by the pressure from above. Hot spouting springs doubtless obey the same laws, the water being heated by volcanic masses in the earth. Boiling springs are found in various countries. Periodical, or intermitting springs, are very curious works of nature. At Como, in Italy, there is one which rises and falls every hour. There is a spring in Provence, in France, which rises eight times in an hour, and another in Languedoc, the period of whose elevation each day, is fifty minutes later than the preceding day. England furnishes examples of several springs which rise and fall with the ebb and flow of the sea.

6. Glaciers. Glaciers, which crown the tops of the highest mountains, have a close connexion with the origin of springs. The snows which have accumulated for whole centuries, sink down and are consolidated by alternate thaws and frosts. Thus the tops of the mountains are covered with ice; these masses gradually extend, and the high valleys become filled. The masses continuing to increase, sometimes for a series of years, even extend to the lower parts of the mountains. They have in Switzerland filled up whole valleys, buried villages, and shut up the pass between Le Valais and the Canton of Berne. The scenes which these bodies of ice present to the traveller, are various and striking; sometimes they resemble the waves of the sea; again they appear like mirrors of brilliant glass. Here a thousand spires glitter in the sunshine; sometimes they assume the appearance of ruins fallen and crushed; and again vast pyramids and obelisks are presented to the astonished beholder.

These glaciers are of essential service in furnishing to the adjacent regions, slowly and in almost a regular manner, waters, which without this congelation would be precipitated with impetuosity from the heights of the mountains, so as to overflow and devastate the countries which they now fertilize.

7. Mineral Springs. The water of springs always contains air and some saline ingredients. In good drinkable water the air is usually equal to about one twenty-fifth of its volume, and the saline contents form about one 6000th of its weight. Such springs are called soft, and answer well for domestic purposes; when the solid ingredients exceed this quantity, the water is hard, and is less fitted for cooking, dissolving soap, &c. When these substances are ir

such quantities as to produce very perceptible effects upon the animal system, or to show decided chemical powers in other ways, the spring becomes a mineral water; if the temperature of the water is above the ordinary temperature, then we have thermal or warm springs. Mineral waters may be, 1. acidulous; 2. chalybeate; 3. sulphureous; 4. saline. The first generally owe their sparkling appearance and acid qualities to fixed air or carbonic acid. Such are the waters of Tunbridge, in England, of Pyrmont, Spa, and Selters, in Europe, and others. The chalybeates generally contain several grains of oxide of iron, mixed with other salts; of this class are the Harrowgate springs, in England, the celebrated springs of Saratoga and Ballston, in New York, and many others in this country. Sulphureous waters owe their qualities to the presence of sulphuretted hydrogen, and some salts in which sulphuric acid is combined (sulphates); such are the fine group of sulphur springs in Western Virginia, and the waters of Aix-la-Chapelle, in Europe. Saline waters contain large quantities of different salts, such as common salt, Epsom, Glauber's salt, &c. Those which have but a small portion of the medicinal salts, are used for the manufacture of common salt, as in New York, Western Virginia, Pennsylvania, and all over the Western States. The source of the peculiar impregnation of these various waters, is the mineral beds through which they flow. The temperature of thermal waters varies from 50° or 60° to boiling point; the Hot Springs of Virginia are about 106, those of Arkansas nearly 200°, and the Geysers of Iceland 212°, or at boiling point. Thermal waters are sometimes pure, and sometimes contain mineral ingredients. In some cases carburetted or sulphuretted hydrogen issues from the ground in great quantities, forming blowing or burning springs. The village of Fredonia, in New York, is lighted by natural gas, supplied in this manner.

8. Rivers. Rivers are natural drains, which convey to the sea that portion of the waters falling upon the earth, which does not pass off by evaporation, or go to nourish organic bodies. The sources of rivers are generally springs, or small streams, fed by the melting of snow and ice upon the mountains, or by rains.

9. Basin. The district from which the waters of a river are derived, is called its basin. The basin is bounded by highlands, which are sometimes mountainous, and which divide it from other basins. The water descending from the water-shed or dividing ridge collects into brooks, the brooks unite into rivulets; the rivulets united form the main trunk or river, which conveys the waters of the whole to the sea. All these descend over inclined planes, so that the lowest point of each brook is that where it joins the rivulet; the lowest point of the rivulet that where it unites with the main stream; and the lowest point in the whole system that where the river falls into the sea. These basins form important natural divisions. Those streams which empty themselves into larger streams are called the tributaries of the latter. The following table shows the length of some of the principal rivers.

10. Bed, Banks, &c. The cavity or channel, in which a river flows is called its bed, and generally has the appearance of having been cut or worn by the current itself. The borders of the channel are called the banks of the river; that bank which is to the right of a person descending the stream, or facing the mouth of the river, is called the right bank, and the opposite is the left bank. The mouth of a river is the point, where it enters into a lake, sea, or another river; in the latter case the point of junction of the two streams is called the confluence.

11. Estuary, Delta. Many of the largest rivers mingle with the sea by means of a single outlet, in which case they often spread into wide expanses, called estuaries or friths. Others before their termination divide into several branches, embracing a triangular space of land called a delta, from its resemblance to the shape of the fourth letter of the Greek alphabet (4).

Falls of Niagara.

12. Falls, Rapids, Bore. When the bed of a river suddenly changes its level, so that the water plunges down a considerable descent, it forms a fall, cascade, or cataract. When its current is accelerated by a considerable inclination in its bed, or broken by a series of descents of little height, it forms rapids. Some streams rush with great force into the sea, carrying a large mass of water, which encounters the ocean tide, advancing in the opposite direction; the collision of the opposing currents produces a tremendous shock; this phenomenon is called a bore. 13. Bars. The opposition which

takes place between the tide and the currents of rivers causes, in many instances, collections of mud or sand at their mouths, which are called bars, on account of the obstruction which they offer to navigation.

14. Periodical Floods. All rivers are more or less subject to occasional or periodical floods or inundations. Within the tropics, these floods are produced by the annual rains, and occur during the summer months, but beyond the tropics, they occur at various seasons, and in high latitudes chiefly in the spring, when the snow and ice melt. In some cases where the river banks are high, the water merely rises in the bed of the river; but where the banks are but little above the level of the river-bed, the waters overflow them, forming vast lake-like expanses.

15. Alluvial Deposits. Rivers which pass through low and level tracts in their annual inundations, deposit the earth, sand, and gravel brought down by their waters, on their banks, and raise them gradually above the surrounding country, while a part of the matter carried to the sea extends the coast, or forms sand or mud banks, which rise by degrees above the water. It is thus that the Ganges, Po, Nile, Mississippi, and many other rivers flow on the top of ridges, behind which are cultivated and inhabited districts, lying lower than the level of the

waters. During floods, the elevated sides are sometimes burst through, and the waters which escape stagnate in temporary lakes, or return into the main stream lower down, or travel to the sea by a separate mouth.

VI. CLIMATE, WINDS, &c.

1. Climate. The term climate expresses the particular combination of temperature and moisture which characterizes the atmosphere of any particular place. We may distinguish in general six different combinations or climates, which, however, are infinitely diversified in degree; thus we have warm and moist, warm and dry, temperate and moist, temperate and dry, cold and moist, and cold and dry climates.

2. Causes of Climate. There are nine circumstances which determine the character of climate 1. The sun's action upon the atmosphere; 2. the temperature of the earth; 3. the elevation of the ground above the level of the ocean; 4. the general slope of the ground and its particular exposure; 5. the position and direction of mountains; 6. the neighborhood and relative situation of great bodies of water; 7. the nature of the soil; 8. the degree of cultivation and density of population; and 9 the prevailing winds.

3. Modifications of Climate. The whole of America, north of latitude 55°, may be considered a frozen region. In Greenland, and around Hudson's Bay, brandy freezes during the winter. The ice and snow accumulate on the land and water, and cover a great part of the country throughout the year. The winter begins in August and continues for 9 months. In summer the heat is as great as in New England. It continues, however, for too short a period to bring grain to maturity, and the cultivation of the soil is very little practised. Vegetation is too scanty to supply the inhabitants with any considerable part of their food; they therefore live chiefly on seals, and other productions of the sea.

Between 55° and 45°, the climate of North America is still severe. In winter, the cold is intense; and the snow, which begins to fall in November, remains till May. The summer advances with such rapidity, that the season of spring is scarcely known. In June the fields and forests are covered with luxuriant verdure. Grass is abundant, and in some parts grain is cultivated with success.

The temperate portions of North America may be considered as extending from 45° to 37° north latitude. These regions are prolific in grass, grain, and various kinds of fruit, as apples, pears, peaches, &c. From 37° north to the latitude of 40° south, the climate is hot, and the products are tobacco, indigo, cotton, rice, and various fruits, and plants called tropical, as oranges, lemons, figs, pine apples, sugar cane, coffee, &c. Beyond latitude 40° south, the climate again becomes cold, and at Terra del Fuego, it is severe. At the Georgian Isles in latitude 54° south, the climate appears to be frigid.

It seems, therefore, that the temperature in general becomes cold or warm as we approach or recede from the equator. Here, beneath a vertical sun, reigns perpetual summer, and nature puts on a magnificent array of vegetation. As if enchanted by these regions, birds of beautiful plumage are seen in flocks amid the ever-verdant groves; monkeys are sporting on the trees, and lurking amid marshes and thickets, are Jaguars, Cougars, and the Jacumana. As we eave these countries and proceed to the north or south, there is a gradual change; not only does vegetation assume a less and less exuberant character, but the trees and plants are exchanged for others. The orange gives place to the peach and vine; these disappear, and the hardier fruits, such as apples and pears, are suspended from the trees. These disappear again, and forests of dark pine cover the land with gloom. These dwindle by degrees, until only here and there a stunted birch, or willow, the hardiest of trees, is found to endure the inhospitable climate.

But while the climate of a country thus chiefly depends upon its nearness to the equator,