As the form of the earth is spherical, it is impossible to represent any considerable portion of its surface on a plane without making some parts appear larger than they are, relatively to others. In maps commonly used in schools, the world is represented in two circles, called the eastern and western hemispheres.

4. The surface of the globe comprises nearly two hundred million square miles, of which only about one fourth part is land, and considerably more than half of this is in the eastern hemisphere. The accompanying chart shows about three times as much land north of the equator as south of it; and it will also be observed that nearly one half of all the land is in the northern temperate zone.

5. If we draw a map with London for the centre of the circle or horizon, which is nearly that of the land hemisphere above represented, we shall include more land than if any other city were taken as a centre, and consequently in the opposite hemisphere there will be more water. In other words, there is more land within 6000 miles of London than within that distance of any other city on the globe. It is often said that certain cities have an extensive "back country" on which they depend for support, and it is an interesting fact that London, the commercial metropolis of the world, has a greater "back country," within the distance of one fourth the earth's circumference, than any other city on the globe.

6. There is a method of representing the earth's surface called Mercator's projection. This method, which is universally adopted for nautical charts, and has many advant

ages for physical maps, has the meridian lines straight, equidistant, and parallel. The parallels of latitude are also straight lines perpendicular to the meridians; but their distances increase from the equator in such proportions as always to show the true bearings of places from one another.* 7. In using Mercator's chart, it must be remembered that it does not truly represent the figure, or relative magnitude of countries, especially those far from the equator. In this kind of chart the surface of the earth is represented as if it were the convex surface of a cylinder, spread out on a levei or plain, and the western continent is often shown on the right side of the map.

LESSON II.-CONTINENTS AND ISLANDS.

1. THERE are three great masses of land on the earth's surface, which, as they are surrounded by water, might be termed islands, but two of these are commonly called continents. These three great divisions are the Old continent, embracing Europe, Asia, and Africa; the New continent, including North and South America; and the island of Australia.

2. The two continents differ remarkably in their general features. In the Eastern continent the general direction of the land and of the great chain of mountains is from east to west, nearly parallel with the equator. In the Western continent the direction of the land is from north to south, or perpendicular to the equator. The Western continent is not quite half as large as the Eastern, but it has about five times the area of Australia.

3. Another notable feature of the land is, that all the great peninsulas are nearly triangular in shape, and are pointed toward the south. Such is the case with Africa, South America, Arabia, Hindostan, Corea, Kamtschatka, California, Greenland, and Florida; a circumstance which the celebrated geololgist, Dr. Buckland, has attributed to the wearing away of the land by the waters of the ocean, which he supposes to have been projected northward from the southern hemisphere with great force by some sudden convulsion of the globe. The only exceptions to this generalization are Yucatan and Jutland, which are alluvial formations, and owe their structure to influences which have not operated in shaping the great continental masses.

* The physical chart of North America, on page 378, is drawn on the plan of Mercator's projection.

4. Each continent has an island or group of islands a little east of its southern extremity; thus South America has its Falkland Islands, and Africa its Madagascar. So also Ceylon is similarly situated in respect to Hindostan; Iceland to Greenland; the Bahamas to Florida; and Tasmania and New Zealand to Australia.

5. It has been observed, as another peculiarity of the structure of peninsulas, that they generally terminate abruptly in bluffs, promontories, or mountains. Thus, at the southern extremity of Africa, the Cape of Good Hope stands out as a rocky barrier, where, in some great convulsion of the globe, the waters of the ocean were stayed; the high, black, and precipitous promontory of Cape Horn is the visible termination of the Andes; and the extremity of the Ghauts Mount ains, in Hindostan, is Cape Comorin. There is also a striking analogy between the unbroken coast-line of South America and Africa, while North America resembles Europe in its coast indentations of bays and gulfs.

6. It is important that a commercial city should have ample wharf-room, which is usually increased artificially, as far as possible, in the construction of slips, piers, and wharves. A similar advantage is presented in the indentation of a coast by seas, gulfs, and bays. In this respect Europe is most fortunate, having one mile of sea-coast for every 156 square miles of surface, while less favored Africa has the same coast-line for every 623 square miles of territory. Next to Europe, North America has the greatest proportionate extent of coast, being one mile for every 350 square miles of surface. Africa," says Prof. Guyot, "is nearly ellipsoidal, and concentrated upon itself. It thrusts into the ocean no important peninsula, nor any where lets into its bosom the waters of the sea. It seems to close itself against every influence from

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without."

7. Though the countless islands scattered over the globe appear so various in size, form, and character, they have been grouped into two distinct classes, called continental and pelagic. Continental islands occur along the margin of continents, which they resemble in geological situation, and are usually long in proportion to their breadth. They seem to have been formed at the same time as the continents, and possibly were once joined to the main land, having been separated by the action of the sea. It may be that the positions

of continental islands mark the former boundaries of the continents. Vancouver's Island, on the western coast of Amer

ica, and the islands from Chiloe to Cape Horn, also the West Indies, England and Scotland, Corsica and Sardinia, and Madagascar, are good examples of continental islands.

8. Pelagic islands are mostly volcanic or coral formations which have risen from the bed of the ocean, far from land, and independent of the continents. In form they are generally round, and are mostly found in groups. Single pelagic islands, like St. Helena, are rare. Although they sometimes rise thousands of feet above the sea, they are probably the tops

of mountains whose bases

are far down in the fathomless retreats of the ocean.

9. In July, 1831, a new volcanic island appeared near Sicily, in the Mediterranean Sea, caused by the bursting forth of a volcano. An island was formed there with a crater in its centre. This was called Graham Island; and although it rose from a part of the sea where the water was 100 fathoms deep, and continued to grow till it was three miles in circumference and above 200 feet high, it afterward gradually diminished in size, and finally, after

a few weeks, disappeared beneath the waves.

1.

LESSON III.-CORAL ISLANDS AND REEFS.

DEEP in the wave is a coral grove,

Where the purple mullet and gold-fish rove,

Where the sea-flower spreads its leaves of blue,

That never are wet with falling dew,

But in bright and changeful beauty shine,

Far down in the green and glassy brine. PERCIVAL.

2. The "great and wide sea, wherein are things creeping innumerable, both small and great beasts," contains countless multitudes of living beings scarcely larger than a pin's head, which are constantly engaged in taking from the sea-water the lime it holds in solution, and, in the form of "coral groves," building up islands and reefs, some of which are a thousand miles in extent. Prof. Dana calculates that there are in the

South Sea nearly 300 coral islands, the work of these "jellylike specks."

3. There are four different kinds of coral formations in the Pacific and Indian Oceans, called lagoon islands or atolls, encircling reefs, barrier reefs, and coral fringes. They are nearly all confined to tropical regions; the atolls to the Pacific and Indian Oceans alone. Atolls, of which the annexed

An atoll of the Pacific Ocean, covered with vegetation.

cut is a fair representation, consist of a circular ring of coral surrounding a shallow lake or lagoon of water. Encircling reefs surround mountainous islands at some distance from the shore. Barrier reefs are similar, but differ in their position in respect to the land. The largest barrier reef is the Australian, which extends more than 1000 miles.

4. On these bare reefs of coral the storms and waves of the ocean gradually deposit mud, sand, and sea-weed, until at length a kind of soil is formed. Seeds from the neighboring or distant lands are driven to the desolate isle, and, finding a soil suited to them, germinate and grow, until finally the ocean rock is covered with verdure. The mariner has visited the "sea-snatched isle," and

"Wandered where the dreamy palm
Murmured above the sleeping wave:
And through the waters clear and calm
Looked down into the coral cave,
Whose echoes never had been stirred
By breath of man or song of bird."

5. The whole of the Pacific Ocean is crowded with islands of the same architecture, the produce of the same insignificant architects. An animal barely possessing life, scarcely appearing to possess volition, tied down to its narrow cell, ephem eral in existence, is daily, hourly creating the habitations of