Part 11

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.

ISLANDS OF THE WORLD

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 AND OCEANIC ISLANDS

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.

FORMS OF VOLCANIC 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.

WONDERFUL STRUCTURE OF CORAL ISLANDS

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=

COMBINATION OF VOLCANIC AND CORAL ISLANDS

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 AND THEIR BUILDERS

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.

Reef-building polyps do not live below the depth of one hundred or one hundred and twenty feet, and hence require a foundation 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.

DISTRIBUTION OF CORALS

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 ATOLL FORM OF ISLAND

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.

=MOST NOTED ISLANDS OF THE WORLD--WESTERN HEMISPHERE=

+--------+---------- | =Area | =Popula- =Name and Sovereignty= | Square | tion= | Miles= | -------------------------------------------+--------+---------- =Anticosti= (to Britain) | 2,600 | 500 =Bahamas= (to Britain) | 4,404 | 58,000 =Bermudas= (to Britain) | 20 | 20,000 =Cape Breton= (to Britain) | 3,120 | 100,000 =Cuba= (Independent) | 44,164 | 2,155,000 =Dominica= (to Britain) | 291 | 35,000 =Falkland= (to Britain) | 5,500 | 3,250 =Feeji, or Feejee= (to Britain) | 7,435 | 155,000 =Galapagos= (to Ecuador) | 2,400 | 400 =Greenland= (to Denmark) | 46,740 | 15,000 =Guadeloupe= (to France) | 688 | 182,000 =Hawaiian= See Sandwich. | | =Isla de Pinos= (Isle of Pines) (to Spain) | 1,200 | 32,000 =Jamaica= (to Britain) | 4,200 | 865,000 =Long Island= (to U. S.) | 1,682 | 2,700,000 =Martinique= (to France) | 378 | 180,000 =New Foundland= (to Britain) | 42,734 | 218,000 =Porto Rico= (to U. S.) | 3,604 | 1,120,000 =Prince Edward= (to Britain) | 2,184 | 94,000 =Santo Domingo= (Independent) | 28,250 | 2,700,000 =Sandwich or Hawaiian= (to U. S.) | 6,449 | 192,000 =Staten Island= (to U. S.) | 65 | 86,000 =Tahiti= (to France) | 1,500 | 30,000 =Tierra del Fuego= (to Argentina) | 18,500 | 1,700 =Trinidad= (to Britain) | 1,750 | 350,000 =Vancouver= (to Britain) | 15,937 | 55,000 -------------------------------------------+--------+----------

=MOST NOTED ISLANDS OF THE WORLD--EASTERN HEMISPHERE=

+--------+---------- | =Area | =Popula- =Name and Sovereignty= | Square | tion= | Miles= | -------------------------------------------+--------+---------- =Balearic Islands= (to Spain) | 1,935 | 326,000 =Borneo= (to Britain and Holland) |284,000 | 2,000,000 =Canary Islands= (to Spain) | 2,807 | 420,000 =Candia, or Crete= (to Turkey) | 3,365 | 243,000 =Cape Verde Islands= (to Portugal) | 1,480 | 148,000 =Celebes= (to Holland) | 71,470 | 2,000,000 =Ceylon= (to Britain) | 25,332 | 3,595,000 =Corsica= (to France) | 3,378 | 290,000 =Cyprus= (to Britain) | 3,584 | 140,000 =Elba= (to Italy) | 85 | 27,000 =England= (Independent) | 88,729 |40,835,000 =Formosa= (to Japan) | 13,458 | 3,392,000 =Gothland= (to Sweden) | 1,217 | 56,000 =Hainan= (to China) | 16,000 | 2,000,000 =Iceland= (to Denmark) | 39,756 | 86,000 =Ireland= (to Britain) | 32,360 | 4,382,000 {Honshiu | 87,485 |37,415,000 =Japan= {Khiushiu | 16,840 | 7,727,000 {Skikoku | 7,031 | 3,290,000 {Hokkaido (Yezo) | 36,299 | 1,140,000 =Java= (to Holland) | 50,554 |30,100,000 =Madagascar= (to France) |227,950 | 2,745,000 =Madeira Islands= (to Portugal) | 314 | 150,600 =Malta= (to Britain) | 117 | 229,000 =New Guinea= See Papua. | | =New Zealand= {N. Island | 44,468 | 564,000 (to Britain) {S. Island | 58,325 | 445,000 =Papua, or New Guinea= (to Britain, | | Germany and Holland) |313,183 | 710,000 {Luzon | 40,969 | 3,800,000 {Mindanao | 36,292 | 500,000 =Philippines= (to U. S.) {Panay | 4,611 | 744,000 {Cebu | 1,762 | 593,000 {Leyte | 2,722 | 358,000 =St. Helena= (to Britain) | 47 | 3,520 =Sakhalin= (Japan and Russia) | 29,000 | 30,000 =Sardinia= (to Italy) | 9,306 | 854,000 =Sicily= (to Italy) | 9,935 | 3,685,000 =Spitzbergen= (to Norway) | 27,000 | ... =Sumatra= (to Holland) |165,000 | 3,200,000 =Van Diemen, or Tasmania= (to Britain) | 26,215 | 197,000 =Zanzibar= (to Britain) | 640 | 115,000 -------------------------------------------+--------+----------

VOLCANOES, GEYSERS AND EARTHQUAKES

CAUSE, STRUCTURE AND LOCATION OF VOLCANOES

The primary cause of volcanoes, as of geysers, earthquakes and other similar phenomena of nature, is the intensely heated condition of the earth’s interior. It is the same force that has produced the irregular features of the earth’s surface--its mighty mountain chains, the sunken basins of the oceans, and its hills, valleys and gorges. Quite logically, volcanoes are most numerous and most intense along the deep mountain fissures which establish a ready communication between the interior and the surface of the earth. Consequently the significant facts about them are: (1) Nearly all volcanoes are either along the highest border of the continents, or in the great central zone of fracture; (2) most of the volcanic groups exhibit a linear arrangement; (3) the agent at work in these mighty engines is mainly vapor of water, or steam power.

WHAT VOLCANOES ARE AND HOW THEY ACT

The form of typical volcanic mountain is that of a cone, with a circular basin or depression, called a crater, at its summit. In the center of the crater is the mouth of a perpendicular shaft or chimney, which emits clouds of hot vapor and gases; and in periods of greater activity, ejects ashes, fragments of heated rock, and streams of fiery lava.

Volcanic ashes, when examined under a microscope, are found to be simply pulverized lava, frequently in minute crystals, and bear no resemblance to ashes in the ordinary sense of the term.

The lava stream, when flowing white hot from the crater, is not unlike a jet of melted iron escaping from a furnace, and moves at first with considerable rapidity. It soon cools on the surface, and becomes covered with a hard, black, porous crust, while the interior remains melted and continues to flow. If the stream is thick, the lava may be found still warm after ten or even twenty years.

The amount of matter ejected by volcanoes is very great. The whole island of Hawaii, the largest of the Hawaiian Islands, seems to be only an accumulation of lava thrown out by its four craters. All high oceanic islands are of the same character. Iceland, with an area of forty thousand square miles, is a vast table-land from three thousand to five thousand feet in elevation, composed of volcanic rock similar to the lavas still ejected by its numerous volcanoes.

VESUVIUS THE MOST REMARKABLE VOLCANO

Nearly all active volcanoes have intervals of comparative repose, interrupted by periods of increased activity, which terminate in a violent ejection of matter from the interior, during which the volcano is said to be in a state of eruption.

The phenomena which characterize these differing phases of volcanic activity may be best made clear by describing them as actually observed in Vesuvius, one of the most carefully studied and most active volcanoes of modern times.

Vesuvius is a solitary mountain rising to the height of nearly 4,000 feet, from the midst of a highly cultivated plain which borders upon the shores of the Bay of Naples. Though the mountain has a regular conical form, two summits, very nearly equal in height, are visible from Naples--Monte Somma on the north, and Vesuvius proper on the south.

The Eruption begins generally with a tremendous explosion which seems to shake the mountain to its very foundations, and hurls into the air dense clouds of vapor and ashes. Other explosions succeed rapidly, and with increasing violence, each sending up a white, globular cloud of steam, or aqueous vapor. This long array of clouds, accompanied by dark ashes, volcanic sand, and fragments of red-hot lava of all sizes, soon forms a stupendous column.

Finally the boiling lava overflows the rim of the crater, and descends in fiery torrents down the slopes; or, bursting the mountain by its weight, finds a vent through some fissure far below the summit. After the expulsion of the lava the eruption is generally near its end, though it does not necessarily terminate at once. Alternate phases of outbursting steam, ashes, and lava may continue with more or less violence for weeks or even months.

The sudden condensation of the enormous accumulation of hot vapor thrown into the air by the eruption, gives rise to striking atmospheric phenomena. Vivid flashes of lightning start from all parts of the column, and play about the clouds above; and often a local thunderstorm, formed in the midst of a clear sky, pours a heavy rain of warm water and ashes upon the slopes of the mountain. The hot, destructive mud torrents, created by these rains, have often been mistaken for lava streams.

The majesty of the spectacle is still greater at night. Though flames of burning gases are of rare occurrence, the clouds and columns of vapor are strongly illuminated by the reflection of the white-hot lava within the crater; and fragments of this lava constantly thrown into the air give the column all the brilliancy of a gigantic piece of fire-work. The sky itself, far and wide, partakes of the same vivid coloring, and the whole scene resembles a vast conflagration.

SIZE AND DISTRIBUTION OF VOLCANOES

In size they vary from mere mounds a few yards in diameter, such as the salses or mud-volcanoes near the Caspian, to Etna, 9,652 feet high, with a base thirty miles in diameter; Cotopaxi, in the Andes, 18,880 feet high; or Mauna Loa, in the Sandwich Isles, 13,600 feet high, with a base seventy miles in diameter and two craters, one of which, Kilauea, is the largest active crater in our earth, being seven miles in circuit.

Two great terrestrial zones include nearly all the known volcanoes of the globe, arranged in long bands or series, or in isolated groups.

FIRST ZONE. This includes the vast array of mountain chains, peninsulas, and bands of islands which encircle the Pacific Ocean with a belt of burning mountains. Within it occur, in the New World: (1) the Andes mountains, with three of the most remarkable series of volcanoes--those of Chili, Bolivia, and Ecuador--separated by hundreds of miles; (2) the volcanic group of Central America; (3) the series of Mexico; (4) the series of the Sierra Nevada and Cascade mountains; (5) the group of Alaska; and (6) the long series of the Aleutian Islands.

In the Old World are: (1) the series of Kamchatka and the Kurile Islands; (2) the group of Japan; (3) the series south of Japan, including Formosa, the Philippine and the Molucca Islands; and (4) the Australian series, including New Guinea, New Britain, New Hebrides, and New Zealand. In this vast zone there are not less than four hundred volcanoes, one hundred and seventy of which are still active.

SECOND ZONE. This contains the belt of broken lands and inland seas, which extending round the globe, separates the northern from the southern continents, and intersects the first zone, in the equatorial regions, nearly at right angles.

In it are: (1) the volcanic regions of Central America and Mexico, and the series of the Lesser Antilles; (2) the groups of the Azores and Canary islands (3) the Mediterranean islands and peninsulas, including all the active volcanoes of Europe; (4) Asia Minor with numerous extinct volcanoes; (5) the shores of the Red Sea and Persian Gulf, and the two Indias, rich in traces of volcanic action; (6) the East Indian Archipelago with hundreds of burning mountains; and (7) the Friendly Islands and other volcanic groups of the central Pacific.

In this zone there are no less than one hundred and sixty volcanoes, so that the two volcanic zones together contain five hundred and sixty, or five-sixths of all known.

ISOLATED VOLCANOES. The volcanoes not included in these two great zones are isolated, in the midst of the oceans, or in the broken polar lands. The most noted are the Hawaiian Island group, in the Pacific; Bourbon and Mauritius, in the Indian Ocean; Cape Verde Islands, Ascension, St. Helena, and Tristan da Cunha, in the Atlantic; Iceland and Jan Mayen, in the Arctic Ocean; and Erebus and Terror, in Antarctic.

=MOST NOTED VOLCANOES=