ated among their summits, and descend in perennial supplies from their glens and recesses. Botanically and zoologically, mountain and plain has each its own peculiarities and numerical abundance of forms-these forms becoming fewer and of less importance as we ascend, and more abundant of higher biological value as we descend into the sheltered and fertile lowland. Ethnologically, as mountain regions have ever been the nursing fields of hardy, brave and independent races; so plains and valleys have ever been the chosen seats of settled industry and civilisation. The plains of China and Hindostan, of the Tigris, the Euphrates, and the Nile, were the early and populous abodes of mankind in the Eastern hemisphere, just as in the Western the valleys of the Missouri and the Mississippi were the chosen grounds of primitive moundbuilding races. And as in former ages, so even now the principal sites and centres of industry are to be found in the river-plains of the Old and New Worlds-the causes that induced the early shepherd settlers being equally operative on their agricultural, citydwelling, mechanical, and commercial descendants.

There is no special work devoted to the plains and valleys of the world; but such books as Humboldt's Views of Nature,’ Balbi's 'Geography,' and the like, contain many isolated descriptions; while books of travel may be consulted for particular accounts of the lowlands in the countries to which they refer. Indeed, the true student of geography will rarely neglect the opportunity of perusing the works of competent travellers, as it is only by such means that he can ever become acquainted with the features of the world in general. No one can know the whole world from his own experience, but it is in the power of every intelligent individual to learn something of its principal aspects by a perusal of the reliable and recorded labours of others.

VIII.

THE WATER-ITS OCEANS AND SEAS.

Their Area and Configuration.

101. HAVING considered the various conditions of the Land-its area, configuration, highlands, and lowlands-we now turn to those of the Water, as exhibited in its oceans and seas, their areas, depths, composition, tides, currents, and kindred phenomena. And here it may be observed of WATER, which forms so important an element in the constitution of the globe, that, chemically speaking, it is the protoxide of hydrogen, consisting of two volumes of hydrogen and one of oxygen, or of eight parts of oxygen to one of hydrogen by weight-88.9 oxygen and 11.1 hydrogen. When pure and at ordinary temperature, it is fluid and amorphous, without taste or smell, colourless in small quantities, but in large masses of a peculiar bluish-green or blue. The specific gravity of pure or distilled water, at 62° Fahr., is assumed at 1.000, and is taken as the standard of gravity for all other bodies; but sea-water varies, according to locality and the depth from which it is taken, from 1.027 to 1.029. When heated to the temperature of 212° Fahr. at the level of the sea, and under the ordinary pressure of the atmosphere, water boils, and is converted into steam; and this boiling point (as it is termed) becomes less as we ascend above the sea-level. In other words, as the pressure of the atmosphere becomes less, ebullition, or the phenomenon of boiling, takes place sooner, and this so uniformly that it is taken, like the barometer, as a measure of ascent or altitude. The effects of boiling at the sea-level, and boiling at an elevation of 12,000 feet, are, however, two very different things: what would be cooked by the former heat, might remain unchanged for hours under the influence of the latter. At 40° Fahr. water is at its minimum volume, expanding as it rises above that temperature, till it is wholly converted into vapour, and also, as it falls below it, till at 32° for

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fresh, and 284° for salt water, it is converted into ice-a transparent, brittle, crystalline solid, which floats on the surface.

102. Water, as found on the earth, is never absolutely pure, but contains more or less of various substances, as atmospheric air, carbonic acid, nitrogen gas; silica, alumina, and salts (carbonates, sulphates, nitrates, phosphates) of lime, magnesia, soda, potash, protoxide of iron, manganese; or chlorides and fluorides of their metallic bases; and in the sea and some saline springs, also iodine and bromine. Like all other fluids whose particles are free to arrange themselves, water at rest always assumes a level surface, and this surface, in the case of the ocean, corresponds with and forms part of the circumference of the globe. As an agent in nature, it is indispensable to the life of plants and animals; it enters into the composition of all bodies, whether organic or inorganic, and in the form of rain, streams, rivers, waves, tides, and currents, is the great modifier and remodeller of the geological aspects of the globe. Water, in fine, is everywhere—in the atmosphere, in visible or invisible form; in the tissues of plants and animals; and in the substance of the rocks and minerals that compose the solid crust. It is the great solvent and circulatory medium in nature, without which life would be impossible, and the inorganic world deprived of its main modeller and modifier.

103. It has already been noticed (par. 41), that though encircling the globe on every side, and spreading over nearly three-fourths of its surface, the great "world of waters" is more or less configured into certain expanses which are termed oceans, and thus we have on the west of the Old World, and between it and the New, the Atlantic Ocean; while on the west of the New World, and between it and the Old, spreads out the still vaster area of the Pacific. These divisions become apparent on the most cursory inspection of the map of the world—the former lying like an irregular valley between the two continental land-masses, and communicating freely with the arctic and antarctic waters; the latter narrowed to a mere strait on the north, but spreading out towards the south over nearly half the globe, and ultimately losing its individuality in the undefined expanse of antarctic waters. Besides the Atlantic and Pacific, the Arctic and Antarctic constitute well-recognised though imperfectly known oceans; while between Africa and Australasia stretches the familiar and muchtraversed area of the Indian Ocean. In treating of these great oceanic expanses, various names and subdivisions are employed by navigators, but for all practical purposes in physical Geography the terms North and South Atlantic, North and South Pacific, Arctic, Antarctic, and Indian Oceans, are sufficiently ex

plicit and comprehensive. Or, looking upon the waters that extend southwards from the extreme points of Africa, Australia, and South America, as one great united mass, the term Southern Ocean will often be found to be convenient, and not inappropriate.

104. Taking the Atlantic Ocean as extending from the arctic to the antarctic circle, its length is upwards of 9000 miles; its breadth varies from 900 to 4000 miles, being only 900 between Norway and Greenland, 1700 between Sierra Leone and Brazil, and 4100 between Marocco and Florida; and its computed area is about 25,000,000 square miles. This vast expanse is little interrupted by islands; in its northern section it is irregular in form, and throws several important branches into the land; but in the southern its form is regular, and its shores continuous. Towards the north it is partly enclosed by the rocky coasts of Greenland, Iceland, and Norway; but towards the south it is quite open, and merges broadly into the Antarctic Ocean. The leading branches are Baffin and Hudson Bays, the Gulf of St Lawrence, Bay of Fundy, Gulf of Mexico, and the Caribbean Sea, on the west or American side; and on the east or Old World side, the North Sea, Baltic Sea, English Channel, Bay of Biscay, the Mediterranean Sea, and the Gulf of Guinea. All, or nearly all, of these recesses occur in the northern division of the Atlantic; hence the greater interest of this section to the geographer, naturalist, and navigator.

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105. Of the minor seas or ramifications belonging to the Atlantic (some of which are ice-locked for a considerable portion of the year, and others encumbered by reefs and shoals), the most important, physically and vitally, is the Mediterranean, whose shores formed the early nurseries of civilisation and commerce, and whose waters are still the highway of communication, not merely between the three continents-Europe, Asia, and Africa-that encircle its shores, but between these and every other portion of the globe. "The political and social events which have occurred on the shores of this remarkable part of the ocean," says Admiral Smyth, closely connected with the history of almost every country in the world; but independently of its classical and historical associations, the Mediterranean still confers invaluable advantages upon the numerous occupiers of its coasts, and through them on the interior of the surrounding continents. It is, moreover, the great bond of intercourse between the nations of Europe, Asia, and Africa, although it appears as if it had been destined to keep them asunder. Beautifully diversified with islands, and bounded by almost every variety of soil, its products are proportionally various; and from its communication with the Atlantic, it facilitates

commerce with every part of the globe. Here navigation made its earliest efforts; and the comparative shortness of the distances between port and port, by rendering the transit easy even to imperfect vessels, tended to promote and diffuse civilisation; it being an unquestionable axiom that whatever is calculated to make men better acquainted with each other, whether the inhabitants of distant lands or neighbours, must invariably produce beneficial results for the whole."

106. The Pacific Ocean, though less important as a highway of commerce, occupies nearly twice the expanse of the Atlantic-its greatest breadth being 12,000 miles, and its computed area about 50,000,000 square miles. Unlike the Atlantic, it is almost entirely shut out from communication with the Arctic Ocean—the only passage of connection being that of Behring Strait, not more than 36 miles in width, with a maximum depth of 25 fathoms; but, like the Atlantic, it also opens out towards the south, and merges undefinedly into the Antarctic. It is thickly studded with islands and clusters of islands, and these physically and vitally constitute one of its most distinctive features. Its leading branches are the Sea of Kamtchatka, Sea of Okhotsk, Sea of Japan, Yellow Sea, and Chinese Sea, on the west or Asiatic side; while on the east or American side, the Gulf of California and the small bay of Panama are the only indentations that break the uniformity of its coasts. The most important of these minor seas are those of Japan and China, whose shores have been the seat of an early and peculiar civilisation, and whose waters have long been traversed by the ships of every other nation.

107. The Indian Ocean, stretching between Africa and Australia on the one hand, and between Asia and the Southern Ocean on the other, is upwards of 4000 miles in breadth, and is computed to have an area of about 17,000,000 square miles. If we except the Indian Archipelago, which forms its boundary rather than belongs to it, it is encumbered by few islands; and it also penetrates the land by few branches—the Red Sea, Arabian Sea, Persian Gulf, and the Bay of Bengal, being the only minor seas -and these all on its northern or Asiatic boundary. The most important of these minor branches are the Red Sea and the Bay of Bengal—the former early and intimately connected with the history of man, and the latter, the leading highway of modern commerce to the varied wealth of India.

108. The Arctic and Antarctic Oceans, from their circumpolar situations, are largely blocked up with ice, and consequently but imperfectly known to geography. The Arctic forms, as it were, a circular basin, bounded in general by the northern coasts of