THE SURFACE OF THE EARTH

GEOLOGICAL MAP OF THE UNITED STATES SHOWING THE REGIONS OF REPRESENTATIVE FORMATIONS

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MAP SHOWING THE DISTRIBUTION OF LAND AND WATER

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The proportion of land to water upon the earth is as 27 to 72, or roughlyone-fourthtothree-fourths; the land covering fifty-three million square miles, the sea one hundred and forty-four million. The land consists of six great bodies called continents, and a multitude of small fragments called islands, which skirt the shores of the continents or dot the broad expanse of the sea.

By far the greatest proportion of land is in the northern hemisphere, and in temperate latitudes. Broadly speaking, the northern hemisphere is the hemisphere of land, and the southern hemisphere is the hemisphere of ocean. The earth could be bisected in such a way that one hemisphere contained almost no land, while the other was composed almost equally of land and water.

The greater part of the land on the earth’s surface is grouped into two greathemispheres, the Old and the New World. The former and far larger of these consists of Eurasia in the north, separated by ill-defined boundaries from Europe to the west and Asia to the east, and of Africa in the south, united to Eurasia by the narrow neck of the isthmus of Suez. The hemisphere of the New World is divided into North America and South America, united by the long, narrow isthmus of Central America. The island of Australia is also reckoned as a continent. It is believed that an island continent, Antarctica, surrounds the South Pole. Of islands not reckoned as continents, the largest is the polar island of Greenland.

In comparing the continents, we at once notice certain resemblances. The first is the tapering to the south, which is seen in Greenland, North and South America, Africa, and Australia (Tasmania). Another is the southward-running peninsulas which characterize Europe and Asia. We may notice, too, that the general lines of the Old World, broad in the north, tapering in the south, resemble those of the New World, especially if we include Australia (Tasmania), and compare its position with that of South America. There is also a certain uniformity in the distribution of relief. Notice the so-called Mid-World and Pacific Mountain systems, which may be traced in the mountains of Central Europe, North Africa, Central Asia, the islands of the Pacific from Japan to New Guinea, and the lofty mountains of North, Central, and South America.

DIAGRAM SHOWING AVERAGE HEIGHT OF THE CONTINENTS

COMPARISON OF THE CONTINENTS

The coast line, or margin of sea and land, is an area rapidly wearing away under the ceaseless influence of the waves, and of the sand and rock, they are perpetually hurling to and fro. Coasts may be either flat or high, composed either of hard or soft rock, and either submerged or raised. A submerged coast is one where the land has sunk or the sea has risen, so that the low grounds and valleys are flooded. A raised coast is one where the land has risen or the sea has retired, and what was formerly the sea bottom is bared.

A flat coast is usually sandy, often bordered by sandhills and lagoons. It may be carved into cliffs, as in the clay cliffs of Norfolk, England. A raised coast is usually flat from the long-continued action of the waves during the period when it was submerged. Flat coasts have no good harbors.

A submerged coast differs according to the nature of the submerged region. If this was hilly or mountainous, with valleys running parallel to the shore, the coast will be ironbound and harbor-less unless the sea-level has risen sufficiently to give access to the valleys behind the first range of heights. If this happens, T-shaped gulfs are formed. Where the valleys open at right angles to the sea, they become bays, usually with excellent harbors. The hills between the valleys rise as peninsulas, or islands. If the land was flat before submerging took place, a flat coast is the result.

Where the land is composed of soft rocks, a more uniform coast-line results than where it is composed of harder rocks, or of hard and soft rocks mixed. The waves, in eating out the softer rocks, often form magnificent sea-caves, natural arches, and pinnacles.

Europesurpasses all the other continents in the magnitude of its indentations and projections. Three great peninsulas—the Balkan peninsula, Italy, and Spain, project into the Mediterranean; while Brittany, Denmark, and Scandinavia jut into the shores of the Atlantic. Even the British Isles are scarcely more than a projection of the continent.

Asiais a second in the relative extent of its peninsula. Asia Minor on the west, Arabia, India, and Indo-China on the south, and China, Manchuria with Corea and Kamchatka, advancing into the waters of the Pacific, form a wide border of projecting lands, containing the richest regions of the continent.

North Americais considerably less indented. Florida, Nova Scotia and Labrador are more prominent on the Atlantic coast, and California Peninsula and Alaska on the Pacific.

The southern continents on the contrary, are nowhere deeply penetrated by the waters of the ocean. The Gulf of Arica in South America, the Gulf of Guinea in Africa, and the Great Australian Bight, are merely gentle bends in the coast line.

Plains occupy nearly one-half of the surface of the continents. They are most extensive and unbroken on the Arctic slopes of the Old World, and in the interior of the two Americas.

Treeless plains, whose vegetation consists of grasses and other herbaceous plants, or stunted shrubs, occur in every continent, and are designated by a variety of terms. Wherever treeless plains are subject to periodical rains, they lose their verdure in the season of drought, and assume the aspect of a desert; but they resume their freshness on the return of the rain, and many are adorned with a great variety of beautiful flowers.

Plains of the Old World.The great Siberian plain extends from the northeastern extremity of Asia to the Ural Mountains and Caspian Sea; and the European plain stretches from the Ural westward, through Russia and North Germany, to the lowlands of Holland.

The plains of the Caspian Sea and western Siberia are dreary steppes, covered with coarse grasses, often growing in tufts, alternating with patches ofheather, furze, dwarf birch, and other stunted shrubs; or old sea bottom, covered with salt efflorescence. Immense reaches of flat country, near the Arctic shores of Asia and Europe, consist of frozen marshes, called tundras, where mosses and lichens are almost the only vegetation. Those of eastern Europe and Asia are denominated steppes; while more limited treeless regions in western Europe are called landes and heaths.

On the alluvial plains of the Old World, civilization began and developed; and their inexhaustible fertility supplied the wants of the most populous nations of antiquity. The great centers of ancient civilization in Egypt, China, India and Babylonia, all had their growth in alluvial plains, built up and fertilized by the mighty rivers which traverse those countries.

Plains of the New World.In North America the greatCentral Plainextends, with but slight interruptions, from the Arctic shores to the Gulf of Mexico. The fertile, treeless plains are termed “prairies” (meadows), while the sterile ones, east of the Rocky Mountains, are known as “the plains.” There are vast cane fields and forests in the lower Mississippi Valley.

In South America the plains of the Orinoco basin, theSelvasof the Amazon, and thePampasof the La Plata, form an uninterrupted series of lowlands which, continued by the plains of Patagonia to the southern extremity of the continent, extend over a distance of three thousand five hundred miles from north to south. The Spanish term “llano” (plain), and the Peruvian “pampa,” designate the treeless plains of the Orinoco and La Plata basins. The Llanos of the Orinoco, during one-half of the year are covered by the richest pasturage, bright with flowers, but during the other half are a parched waste. The Selvas of the Amazon, a luxuriant forest, cover more than a million square miles; and the treeless Pampas, with their tall grasses and thickets of clover and thistles, illustrate the endless richness and variety of nature.

Alluvial and marine plains generally have but a slight altitude, while the undulating plains are sometimes considerably elevated. The Mississippi Valley, at St. Louis, one thousand miles from the ocean, is hardly four hundred feet above the sea-level; and the Amazon, at an equal distance from the sea, does not reach two hundred and fifty feet. The marine plains adjacent to the Caspian and Aral seas are still lower, the larger portion being below the sea-level.

Plateaus are situated either between two lofty mountain chains, which form their margins, or descend by successive terraces to the nearest seas; or they pass, by gradations, from the base of high mountains to the low plains in the interior of the continents.

The Great American Basin, between the Rocky and Sierra Nevada Mountains, and the plateau of Tibet, between the Himalaya and Kuenlun mountains, are examples of the first position; and the table-land of Mexico, of the second. The third is seen in the high plains at the eastern foot of the Rocky Mountains, which descend from an altitude of five thousand or six thousand feet, at the foot of the mountains, to the low plains of the Mississippi basin.

The plateaus most remarkable for their elevation are, Tibet, from ten thousand to eighteen thousand feet above the sea; and the elongated valley-like highlands, from ten thousand to thirteen thousand feet high, between the two chains of the Andes, in South America. East Turkestan and Mongolia, in central Asia; the plateau of Iran, in western Asia; Abyssinia, and the vast plateau which occupies all the southern part of Africa; and the broad table-land which fills the western half of North America with a continuous mass of high land, range in height from four thousand to eight thousand feet.

The great peninsulas of Deccan, Arabia, Asia-Minor and Spain, the central plateau of France, and those of Switzerland, Bavaria, and Transylvania, vary from one thousand to four thousand feet in elevation.

The nature of the soil and climate of great plateaus is in general such as to render them the least useful portions of the continents. Sahara, with an average altitude of 1,000 feet, and the higherplateaus of Mongolia, Iran and parts of the American Basin, may serve as types.

Their surface consists of hardened sand and rock; of hillocks and plains of loose sand constantly shifting by the wind; and of immense tracts, as in Mongolia, covered with pebbles varying from the size of a walnut, or even less, to a foot in diameter: all indicating the original transporting, grinding and depositing of these materials by water.

Salt lakes without outlet occur in each, and salt efflorescence often covers the ground. A lack of rain to wash from the soil substances injurious to vegetation, and supply the water necessary for the growth of plants, leaves these plateaus generally sterile, and some of the most extensive are in part, if not wholly, deserts.

Mountains rise in long and comparatively narrow lines or ridges, the tops of which are often deeply indented, presenting to the eye the appearance of a series of peaks detached one from another. As each of these peaks or distinct elevations is called a mountain and often receives a separate name, the common designation chain or range of mountains is naturally applied to the whole.

The top of the ridge, from which the waters descend on opposite sides, is called the crest; and the notches between the peaks, from which transverse valleys often stretch like deep furrows down the slopes of the chain, are called passes.

Mountain chains are seldom isolated, but are usually combined intosystems, consisting of several more or less parallel and connected chains, with their intervening valleys,—as the Appalachian system, the Alps, and the Andes.

Most mountain chains seem to have been produced by tremendous lateral pressure in portions of the Earth’s crust, causing either long folds, or deep fissures with upturned edges rising into high ridges, the broken strata forming ragged peaks.

Mountains by folding are generally of moderate elevation, while mountains by fracture include the highest chains of the globe. The Appalachian Mountains in North America, and the Jura in Europe, are examples of the first; the Rocky Mountains, Andes, Alps and Himalayas, of the second.

Folded mountains are curved into long arches, either entire or broken at the summit and forming a system of long, parallel ridges, of nearly equal height, separated by trough-like valleys. Here and there, however, deep gaps, or gorges, cut the chains allowing the rivers to escape from one valley to another.

In systems of mountains produced by fracture, there is usually one main central chain, with several subordinate ranges. They have, however, less regularity and similarity among themselves than the parallel chains of mountains by folding.

The crests are deeply indented, cut down one-third or one-half the height of the range, forming isolated peaks and passes which present to the eye the appearance of a saw, called in Spanish Sierra; in Portuguese, Serra. Such ranges are frequently distinguished by these terms, as the Sierra Nevada, in North America; and the Serra do Mar, in Brazil.

Valleys among mountains owe their existence primarily to folds or fissures in the Earth’s crust, produced in the upheaving of the ranges; but they are subsequently deepened, widened and otherwise changed in form and extent, by the action of rains and frosts, and the streams to which they furnish a pathway. Most of the Alpine lakes, celebrated for their picturesque beauty, occupy deep basins at the outlet of transverse valleys.

Valleys in plains and plateaus are mainly, if not entirely, the result of the erosion, or wear of the surface, by running water.

Little rills, formed by the rains or issuing from springs, set out on their course down the slope of the ground, each wearing its small furrow in the surface. Uniting they form a rivulet which wears a broader and deeper channel; and the rivulets in turn combining, form rivers which produce still greater effects.

The great basin of the Mississippi for example, is one grand central valley, cut by the main stream in the line of lowest level, towards which the valleys of the Missouri, the Arkansas, the Ohio, and a multitude of smaller streams, all converge.

MountainsMountainsMountainsMountainsCELEBRATED MOUNTAIN PEAKS THAT STAND AS THE EARTH’S GREATEST SENTINELS1.Mount Everest, the loftiest mountain in the world, is situated in Nepal, India, and rises to an ascertained height of 29,000 feet—almost six miles. It was named for Sir George Everest, an English engineer, and outline Surveyor-General of India. Everest is only one of numerous gigantic peaks of the Himalayas—often called the “Roof of the World”—and is apparently guarded against all attempts at ascent by a rampart of lofty pinnacles. It is best viewed from a point near Darjeeling, India, one hundred and twenty miles distant. From this point travelers are enthralled with the glistening peak of mountain piles as nowhere else on earth. Though a thousand times described, the view is so surpassingly sublime that its full glory can never be depicted in words.2.Mont Blanc(mòn-blon-g) is the highest mountain in Europe, and of the Alps. It is located between Great and Little St. Bernard passes, on the frontier of France, Switzerland and Italy; and is best seen and approached from the village of Chamounix (shä-mo-nē´), France. It was first ascended in 1786, but frequently since, and, in 1893, an observatory was built on its summit. The Mont Blanc chain is famous for glaciers. Many great poets have described the majesty of Mont Blanc, among them, Goethe, Victor Hugo, Byron, Shelley, Wordsworth, and Coleridge.3.The Matterhorn, or Mount Cervin, a splendid mountain obelisk, towers above Zermatt, Switzerland, on the Italian border. The eastern side seems almost vertical, and its ascent is very difficult; hence its name which is due to the formation of the rocky, horn-shaped peak. The loss of life attending its ascent has given the Matterhorn the grim name “Fatal Mountain.”4.Monte Rosa(mŏn´te rō´sa), “rosy mountain,” is next to Mont Blanc, the highest Alpine peak. It is the border between Italy and Switzerland, sixty miles north of Turin, Switzerland. Unlike the Matterhorn, Monte Rosa is easy of ascent and is frequently climbed by ladies. Its name refers to the glaciers which abound and reflect beautiful colors.5.Jungfrau(yung´frau), “virgin,” is one of the Bernese Alps, Switzerland, thirteen miles from Interlaken. It is so named from the pure whiteness of its snowclad peak. A wonderful mountain railway now reaches to the summit, most of the line being through tunnels. Jungfrau is 13,670 feet high.

Mountains

CELEBRATED MOUNTAIN PEAKS THAT STAND AS THE EARTH’S GREATEST SENTINELS

1.Mount Everest, the loftiest mountain in the world, is situated in Nepal, India, and rises to an ascertained height of 29,000 feet—almost six miles. It was named for Sir George Everest, an English engineer, and outline Surveyor-General of India. Everest is only one of numerous gigantic peaks of the Himalayas—often called the “Roof of the World”—and is apparently guarded against all attempts at ascent by a rampart of lofty pinnacles. It is best viewed from a point near Darjeeling, India, one hundred and twenty miles distant. From this point travelers are enthralled with the glistening peak of mountain piles as nowhere else on earth. Though a thousand times described, the view is so surpassingly sublime that its full glory can never be depicted in words.

2.Mont Blanc(mòn-blon-g) is the highest mountain in Europe, and of the Alps. It is located between Great and Little St. Bernard passes, on the frontier of France, Switzerland and Italy; and is best seen and approached from the village of Chamounix (shä-mo-nē´), France. It was first ascended in 1786, but frequently since, and, in 1893, an observatory was built on its summit. The Mont Blanc chain is famous for glaciers. Many great poets have described the majesty of Mont Blanc, among them, Goethe, Victor Hugo, Byron, Shelley, Wordsworth, and Coleridge.

3.The Matterhorn, or Mount Cervin, a splendid mountain obelisk, towers above Zermatt, Switzerland, on the Italian border. The eastern side seems almost vertical, and its ascent is very difficult; hence its name which is due to the formation of the rocky, horn-shaped peak. The loss of life attending its ascent has given the Matterhorn the grim name “Fatal Mountain.”

4.Monte Rosa(mŏn´te rō´sa), “rosy mountain,” is next to Mont Blanc, the highest Alpine peak. It is the border between Italy and Switzerland, sixty miles north of Turin, Switzerland. Unlike the Matterhorn, Monte Rosa is easy of ascent and is frequently climbed by ladies. Its name refers to the glaciers which abound and reflect beautiful colors.

5.Jungfrau(yung´frau), “virgin,” is one of the Bernese Alps, Switzerland, thirteen miles from Interlaken. It is so named from the pure whiteness of its snowclad peak. A wonderful mountain railway now reaches to the summit, most of the line being through tunnels. Jungfrau is 13,670 feet high.

6.Mount Elburzis one of the loftiest and most impressive of all the Caucasian mountains. It is an extinct volcano with two peaks, the western peak 18,470 feet above sea-level, and the other 18,347 feet. It is covered with glaciers, and constitutes a watershed which divides Asia from Europe. The Caucasus gave its name to that great branch of the human race that has ruled the world for many generations.

7.Mount Sinai(si´nāor-nī), famous as the sacred mountain on which Moses received the Ten Commandments, is an individual peak in a vast rocky mass that almost fills the peninsula of Sinai between the Gulf of Suez and Gulf of Akaba. It is named fromSin, the Babylonian moon-god. At its foot, in a ravine, is the monastery of St. Catherine, founded by the Emperor Justinian; a short distance from it the Chapel of St. Elias (Elijah); while on its summit is a little pilgrim church. Its height is 8,593 feet.

8.Pike’s Peak.This famous mountain is six miles from Colorado Springs, Colorado, and may be ascended by a cog railway. It is one of the best-known summits of the Rocky Mountains, and rears its snowy crest to a height of 14,134 feet. On its top is one of the highest weather stations in the world. The view from the observatory is superb, embracing thousands of square miles of mountain and plain.

9.Mount St. Elias, on the Alaskan side of the Canadian frontier, was long considered the highest peak in North America. It is a volcanic mountain, stands in a wild, inaccessible region, and is clothed almost from base to summit with eternal snow. Besides, there are huge glaciers, impassable precipices and yawning chasms. Its height is 18,020 feet. It was ascended by the Duke of the Abruzzi in 1897.

10.Mount Assiniboine(as-sin´i-boin) is frequently called the “Matterhorn of the Canadian Rockies”. It is 11,860 feet in height, and is located near the boundary of British Columbia and Alberta, about twenty miles south of Banff, in one of the most beautiful scenic regions in America. In the immediate vicinity there are geysers, caves, waterfalls, numerous lakes, natural bridges, and glaciers.

11.Mount Popocatepetl(pō-pō-kă-tā-pet´l) is one of the giant volcanic peaks standing guard over Mexico City. Its summit is perpetually covered with snow, but it may be ascended from Popo Park, the terminal of the railway which climbs its slope, to a height of 8,000 feet. The peak itself is 17,887 feet, at the apex of which is a huge crater sheathed with ice, from which clouds of vapor are continually ascending. No great eruption, however, has taken place since 1540. The most imposing spectacle of all from the summit is the remarkable formation of clouds below.

12.Mount Salcantay, one of the most beautiful peaks of the Andes, in Peru, is 21,000 feet in height. Its grandeur is enhanced by the presence of glaciers and the enveloping clouds. It rises to a sharp point with its sides covered with snow and ice, and lifts its head magnificently thousands of feet higher than the surrounding mountains. It has been recently explored by the Yale University expedition.

13.Mount Robson, the highest point in the Canadian Rockies, reaches an elevation of 13,700 feet. It is on the border between Alberta and British Columbia, one of the remarkable “show places” of the Canadian Rockies. All around it is the finest of scenery—huge mountains, snow-crested peaks, rushing rivers that swirl and foam, mysterious canyons and earth-strewn boulders.

14.Mount Rainier(rā´ner) an isolated mountain of the Cascade Range, forty miles southeast of Tacoma, Washington, is an extinct volcano, 15,529 feet in height. There are still two craters at the summit which give off heat and sulphurous fumes. Thick forests cover the lower region of the mountain, while higher up there are fourteen glaciers. It is difficult of ascent, though frequently made. A bridle path leads to a point over 7,000 feet in elevation from which a magnificent view of several of the glaciers may be had.

Mount Ararat, famed as the mountain where Noah’s ark landed after the flood, as recorded in Genesis, is in the Turkish province of Armenia. Ararat is really a twin mountain, the two peaks of which are about seven miles apart, with an elevation of about 17,000 and 13,000 feet, respectively. They rise above a beautiful alluvial plain, and quite naturally the higher peak—Great Ararat—is the one made historically immortal as the motherland of the human race. From their isolation and bareness the two peaks are very impressive, and it is little wonder that Armenia regards these mountain tops as a crown of glory and all other lands as her daughters. Within her borders, too, she gives rise to the beautiful rivers Euphrates, Tigris, Pison, Araxes, and many others. The first modern ascent of the mountain was made in 1829, though often since.

Wonderful examples of valleys by erosion occur in the plateaus adjacent to the Rocky Mountains. The Grand Canon of the Colorado, three hundred miles long, has a depth of from three thousand to six thousand feet below the surrounding country. The sides of this tremendous gorge, which are nearly or quite precipitous, exhibit the successive geological strata down to the oldest rocks. A similar formation exists in the upper course of the Yellowstone, one of the main tributaries of the Missouri, and to a less extent in all the streams flowing through the high barren plateaus.

Valleys descending the slopes of mountains are formed in the same manner. The gathering drops make the rill, and the rill its little furrow; rills combine into rivulets, and rivulets make a gully down the hill-side; rivulets unite to form torrents, and these work with accumulating force, and excavate deep gorges in the declivities. Other torrents form in the same manner about the mountain ridge, and pursue the same work of erosion until the slopes are a series of valleys and ridges, and the summit a bold crest overlooking the eroding waters. The larger part of the valleys of the world are formed entirely by running water.

The multitude of small and apparently fragmentary bodies of land, called islands, form only about one-seventeenth part of the entire land surface of the globe.

Continental islands are situated in the immediate vicinity of the continents, and form properly a part of the continental structure. They have the same kinds of rocks and mountain forms, and the same varieties of plants and large animals, which are found on the neighboring coasts of the mainland.

The size of this class of islands varies extremely. Some are mere isolated rocks, while others occupy large areas, like the British Isles, Japan Islands and Madagascar; or, more extensive still, Papua and Borneo, each of which has an area exceeding two hundred thousand square miles.

The distinctive character of Oceanic islands is that they lie at a distance from the continents, in the midst of the ocean basins. They are always small, and, though sometimes forming lines, or bands, they more frequently occur in groups.

The rocks which make up the body of the continents and continental islands—sandstone, slate, granite, and the various metamorphic rocks—are entirely wanting in oceanic islands. The latter are composed either of volcanic substances, or of limestone. Hence they present much less variety in relief forms than the continental islands.

The islands of volcanic origin are more or less circular in outline; are usually considerably elevated, with rapid slopes; and are of moderate size. Sometimes two or more volcanoes, clustered together, form a single island of larger size and more irregular outline.

Occasional islands rise but little above the surface of the sea, their craters being filled by sea water. Many, however, rise to Alpine heights—like the peaks of Hawaii, in the Hawaiian Islands, nearly fourteen thousand feet in elevation; Pico de Teyde, in the Canaries, fourteen thousand feet; and Tahiti, in the Society Islands, over seven thousand feet above the level of the sea.

Coral islands are among the most striking phenomena of the tropical seas. Whitsunday Island in the midst of the Pacific is an excellent example. Rising but a few feet above the surface of the ocean, it forms a narrow, unbroken, nearly circular ring, surrounding a central lagoon of quiet water. When first seen, it presents the aspects of an angry surf breaking on a white beach of coral sand, in strong contrast with the deep blue color of the sea. Behind this a garland of luxuriant vegetation, whose tropical beauty, enhanced by the noble cocoa-palm encircles the quiet waters of the lagoon, while all around spreads the broad blue sea.

TWO OF THE GREATEST MARVELS OF LAND AND SEA

THE GRAND CANYON OF THE COLORADO RIVER, ARIZONAThis greatest of nature’s gorges is more than twelve miles across, a mile deep, and extends over two hundred miles in length. This whole vast space has been sculptured by the wear of the river through countless centuries. Its unparalleled magnitude, its architectural forms and suggestions, and its wealth of color effects create a picture that is grand beyond description.

THE GRAND CANYON OF THE COLORADO RIVER, ARIZONA

This greatest of nature’s gorges is more than twelve miles across, a mile deep, and extends over two hundred miles in length. This whole vast space has been sculptured by the wear of the river through countless centuries. Its unparalleled magnitude, its architectural forms and suggestions, and its wealth of color effects create a picture that is grand beyond description.

THE BARRIER CORAL REEF OF AUSTRALIAThis vast reef of coral islands was built by a colony of coral insects, or polyps, as innumerable as the stars of the Milky Way. It rose from the floor of the ocean, builded out of myriads upon myriads of the dead skeletons of these marvellous insects.

THE BARRIER CORAL REEF OF AUSTRALIA

This vast reef of coral islands was built by a colony of coral insects, or polyps, as innumerable as the stars of the Milky Way. It rose from the floor of the ocean, builded out of myriads upon myriads of the dead skeletons of these marvellous insects.

A large number of volcanic islands in the Pacific are encircled by coral reefs, which, when near the shore, are called fringing reefs. When at a considerable distance, leaving a lagoon of quiet water between them and the volcanic island, they are termed barrier reefs.

Coral reefs are masses of limestone originally secreted, in the form of coral, by minute polyps which live in countless numbers in the tropical seas. The coral produced by a single community of polyps grows chiefly upward; but multitudes of distinct communities often live so near together that the small lateral growth of each brings them into contact.

Their separate, fragile structures, gradually broken up and compacted by various means, are in time transformed into a solid mass, forming walls of coral rock frequently of enormous extent. The great barrier reef near the northeastern shores of Australia, the longest known, is not less than one thousand two hundred and fifty miles in length.

A LIVING SINGLE CORAL FROM THE PACIFIC OCEANThe coral polyp is one of the master-builders of the world. It may be likened to a sea-anemone, but is inferior in muscular organism, and immensely superior in defensive organization.

A LIVING SINGLE CORAL FROM THE PACIFIC OCEAN

The coral polyp is one of the master-builders of the world. It may be likened to a sea-anemone, but is inferior in muscular organism, and immensely superior in defensive organization.

Reef-building polyps do not live below the depth of one hundred or one hundred and twenty feet, and hence require afoundation near the surface. This is supplied by submarine mountains and plateaus, or the slopes of those volcanic cones which form the high islands.

Growing vertically, the reefs repeat at the surface the outlines of their bases, which fact gives rise to the circular figure both of atolls and reefs in mid-ocean, and to the elongated, wall-like form of reefs adjacent to the continents, like those of Florida and of Australia.

Reef-building polyps are confined to the tropical seas, where the winter temperature is not below sixty-eight degrees. Coral formations are most extensive in the Pacific Ocean, especially south of the Equator, and in the two great archipelagoes of the East and West Indies; but a large number of coral islands also occur in the Indian Ocean. The Coral Sea, east of northern Australia, is particularly remarkable for the great extent of its coral reefs.

The usual form of coral islands is that of a broken ring, numerous channels affording entrance into the lagoon. Such a group of islands is called an atoll, a Malay term, which has been adopted to designate these singular structures. The central lagoon enclosed by an atoll, is invariably shallow, seldom exceeding a few scores, or at most hundreds, of feet in depth; while the outer sea reaches a depth of thousands of feet at a short distance from the shore, showing that the atoll rests upon a submarine mountain.

Atolls are often clustered together in large numbers, forming extensive archipelagoes. Paumotu, or Low Archipelago, numbers eighty coral islands, nearly all of which are atolls; the Caroline, Gilbert and Marshall islands together contain eighty-four atolls, while the Laccadive and Maldive islands form two long double series of atolls extending eight hundred miles from north to south.

MAP SHOWING COMPARATIVE SIZE OF ISLANDS

(Seenext pagefor the Area, Population and Countries to which these islands belong).

ISLANDS OF WESTERN HEMISPHERE

Large illustration(404 kB)

MOST NOTED ISLANDS OF THE WORLD—WESTERN HEMISPHERE

MAP SHOWING COMPARATIVE SIZE OF ISLANDS

ISLANDS OF EASTERN HEMISPHERE

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