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The World's Greatest Books [Volumes 1-15, 17-20]
- Автор: Gutenberg
- Год: 1910
- Язык: английский
- Жанр: Культурология
Электронная книга - «The World's Greatest Books [Volumes 1-15, 17-20]». Краткое содержание книги:
The World's Greatest Books — Volume 01 — Fiction от Неизвестный
The World's Greatest Books — Volume 02 — Fiction от Неизвестный
The World's Greatest Books — Volume 03 — Fiction от Неизвестный
The World's Greatest Books — Volume 04 — Fiction от Неизвестный
The World's Greatest Books — Volume 05 — Fiction от Неизвестный
The World's Greatest Books — Volume 06 — Fiction от Неизвестный
The World's Greatest Books — Volume 07 — Fiction от Неизвестный
The World's Greatest Books — Volume 08 — Fiction от Неизвестный
The World's Greatest Books — Volume 09 — Lives and Letters от Неизвестный
The World's Greatest Books — Volume 10 — Lives and Letters от Неизвестный
The World's Greatest Books — Volume 11 — Ancient and Mediæval History от Неизвестный
The World's Greatest Books — Volume 12 — Modern History от Неизвестный
The World's Greatest Books — Volume 13 — Religion and Philosophy от Неизвестный
The World's Greatest Books — Volume 14 — Philosophy and Economics от Неизвестный
The World's Greatest Books — Volume 15 — Science от Неизвестный
The World's Greatest Books — Volume 17 — Poetry and Drama от Неизвестный
The world's greatest books от Mee, Arthur, 1875-1943, joint editor & Hammerton, John Alexander, Sir, 1871-1949, joint editor & McClure, S. S. (Samuel Sidney), 1857-1949, joint editor
The World's Greatest Books — Volume 19 — Travel and Adventure от Неизвестный
The World's Greatest Books — Volume 20 — Miscellaneous Literature and Index от Неизвестный
II.—Changes in the Inorganic World now in Progress
The great agents of change in the inorganic world may be divided into two principal classes—the aqueous and the igneous. To the aqueous belong rain, rivers, springs, currents, and tides, and the action of frost and snow; to the igneous, volcanoes and earthquakes. Both these classes are instruments of degradation as well as of reproduction. But they may also be regarded as antagonist forces, since the aqueous agents are incessantly labouring to reduce the inequalities of the earth's surface to a level; while the igneous are equally active in restoring the unevenness of the external crust, partly by heaping up new matter in certain localities, and partly by depressing one portion of the earth's envelope and forcing out another.
We will treat in the first place of the aqueous agents.
Rain and Rivers. When one considers that in some parts of the world as much as 500 or 600 inches of rain may fall annually, it is easy to believe that rain qua rain may be a denuding and plastic agent, and in some parts of the world we find evidence of its action in earth pillars or pyramids. The best example of earth pillars is seen near Botzen, in the Tyrol, where there are hundreds of columns of indurated mud, varying in height from 20 feet to 100 feet. These columns are usually capped by a single stone, and have been separated by rain from the terrace of which they once formed a part.
As a rule, however, rain acts through rivers. The power of rivers to denude and transport is exemplified daily. Even a comparatively small stream when swollen by rain may move rocks tons in weight, and may transport thousands of tons of gravel. The greatest damage is done when rivers are dammed by landslips or by ice. In 1818 the River Dranse was blocked by ice, and its upper part became a lake. In the hot season the barrier of ice gave way, and the torrent swept before it rocks, forests, houses, bridges, and cultivated land. For the greater part of its course the flood resembled a moving mass of rock and mud rather than of water. Some fragments of granite rock of enormous size, which might be compared to houses, were torn out and borne down for a quarter of a mile.
The rivers of unmelted ice called the glaciers act more slowly, but they also have the power of transporting gravel, sand, and boulders to great distances, and of polishing and scoring their rocky channels. Icebergs, too, are potent geological agents. Many of them are loaded with 50,000 to 100,000 tons of rock and earth, which they may carry great distances. Also in their course they must break, and polish, and scratch the peaks and points of submarine mountains.
Coast ice, likewise, may transport rocks and earth. Springs also must be considered as geological agents affecting the face of the globe.
But running water not only denudes it, but also creates land, for lakes, seas, rivers are seen to form deltas. That Egypt was the gift of the Nile was the opinion of the Egyptian priests, and there can be no doubt that the fertility of the alluvial plain above Cairo, and the very existence of the delta below that city, are due to the action of that great river, and to its power of transporting mud from the interior of Africa and depositing it on its inundated plains as well as on that space which has been reclaimed from the Mediterranean and converted into land. The delta of the Ganges and Brahmapootra is more than double that of the Nile. Even larger is the delta of the Mississippi, which has been calculated to be 12,300 square miles in area.
Tides and Currents. The transporting and destroying and constructive power of tides and currents is, in many respects, analogous to that of rivers, but extends to wider areas, and is, therefore, of more geological importance. The chief influence of the ocean is exerted at moderate depths below the surface on all areas which are slowly rising, or attempting, as it were, to rise above the sea; but its influence is also seen round the coast of every continent and island.
We shall now consider the igneous agents that act on the earth's surface. These agents are chiefly volcanoes and earthquakes, and we find that both usually occur in particular parts of the world. At various times and at various places within historical times volcanic eruptions and earthquakes have both proved their potency to alter the face of the earth.
The principal geological facts and theories with regard to volcanoes and earthquakes are as follows.
The primary causes of the volcano and the earthquake are to a great extent the same, and connected with the development of heat and chemical action at various depths in the interior of the globe.
Volcanic heat has been supposed to be the result of the original high temperature of the molten planet, and the planet has been supposed to lose heat by radiation. Recent inquiries, however, suggest that the apparent loss of heat may arise from the excessive local development of volcanic action.
Whatever the original shape of our planet, it must in time have become spheroidal by the gradual operation of centrifugal force acting on yielding materials brought successively within its action by aqueous and igneous causes.
The heat in mines and artesian wells increases as we descend, but not in uniform ratio in different regions. Increase at a uniform ratio would imply such heat in the central nucleus as must instantly fuse the crust.
Assuming that there are good astronomical grounds for inferring the original fluidity of the planet, yet such pristine fluidity need not affect the question of volcanic heat, for the volcanic action of successive periods belongs to a much more modern state of the globe, and implies the melting of different parts of the solid crust one after the other.
The supposed great energy of the volcanic forces in the remoter periods is by no means borne out by geological observations on the quantity of lava produced by single eruptions in those several periods.
The old notion that the crystalline rocks, whether stratified or unstratified, such as granite and gneiss, were produced in the lower parts of the earth's crust at the expense of a central nucleus slowly cooling from a state of fusion by heat has now had to be given up, now that granite is found to be of all ages, and now that we know the metamorphic rocks to be altered sedimentary strata, implying the denudation of a previously solidified crust.
The powerful agency of steam or aqueous vapour in volcanic eruptions leads us to compare its power of propelling lava to the surface with that which it exerts in driving water up the pipe of an Icelandic geyser. Various gases also, rendered liquid by pressure at great depths, may aid in causing volcanic outbursts, and in fissuring and convulsing the rocks during earthquakes.
The chemical character of the products of recent eruptions suggests that large bodies of salt water gain access to the volcanic foci. Although this may not be the primary cause of volcanic eruptions, which are probably due to the aqueous vapour intimately mixed with molten rock, yet once the crust is shattered through, the force and frequency of eruptions may depend in some measure on the proximity of large bodies of water.
The permanent elevation and subsidence of land now observed, and which may have been going on through past ages, may be connected with the expansion and contraction of parts of the solid crust, some of which have been cooling from time to time, while others have been gaining heat.
In the preservation of the average proportion of land and sea, the igneous agents exert a conservative power, restoring the unevenness of the surface which the levelling power of water in motion would tend to destroy. If the diameter of the planet remains always the same, the downward movements of the crust must be somewhat in excess, to counterbalance the effects of volcanoes and mineral springs, which are always ejecting material so as to raise the level of the surface of the earth. Subterranean movements, therefore, however destructive they may be during great earthquakes, are essential to the well-being of the habitable surface, and even to the very existence of terrestrial and aquatic species.