Читать книгу Familiar Talks on Science: World-Building and Life; Earth, Air and Water - Gray Elisha - Страница 9

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"In the beginning God created the heaven and the earth. And the earth was without form, and void."

Whatever our speculations may be in regard to a "beginning," and when it was, it is written in the rocks, that, like the animals and plants upon its surface, the earth itself grew; that for countless ages, measured by years that no man can number, the earth has been gradually assuming its present form and composition, and that the processes of growth and decay are active every hour.

The science that deals with the formations and stratifications that are found on the earth and under the earth, and all the forces that have been and are now active in their formation, is called Geology (earth science). It is a science about which little is known by the average individual, and yet it is one of transcendent interest, from the study of which the lover of nature can obtain a vast amount of profit and pleasure. When the uncultured man sees a stone in the road it tells him no story other than the fact that he sees a stone and that it would better be removed; and all the satisfaction he gets out of it is in the thought that he has saved some unlucky wagon wheel from being wrenched or broken. The scientist looking at the same stone perhaps will stop, and with a hammer break it open, when the newly exposed faces of the rock will have written upon them a history that is as real to him as the printed page. He is carried back to a far-off time, where he sees the processes and forces at work that have formed this stone and made it what it is, not only in its outward form, but in its constitution, down to its molecules and atoms. (The word "atom" is used in chemistry to mean the smallest particle of an elementary substance that will combine with the atoms of another substance to form new compounds of matter. And molecules are made up of atoms.) The scientist looking at this stone sees in it not only that mechanical and chemical agencies have cooperated in the work of its formation, but that animal life itself may have been the chief agency in bringing the materials together and giving form to the peculiar architecture employed in its formation. If it is a piece of limestone this latter statement will be eminently true.

Here is a powerful motive for the study of physical science. It is not to be expected, nor is it possible, that every individual can be a scientist in the strict sense of the word, but it is possible for everyone of ordinary intelligence to become familiar with the salient facts of science, if only a small portion of the time that is now devoted to the reading of literature that is rather harmful than helpful be spent in studying the phenomena and works of nature.

The acquirement of such knowledge would furnish every individual with a constant source of instructive amusement that would never lose its interest. He would not be dependent every hour upon people and things outside of himself; because he would carry about with him inexhaustible sources of instruction and pleasure that would furnish him continual and helpful diversion and save him from a thousand morbid tendencies that are always ready to seize upon an unemployed mind. There are many men and women in the insane asylum to-day for the simple reason that they have not made intelligent use of the mental powers that nature has endowed them with.

Sermons are not always preached from pulpits. They are written in the rocks and on the flowers of the field and the trees of the forest.

Let us then look a little at the underground foundation of all this beautiful earth. And before attempting that, the question may arise in some minds how we know what is so deep down under the surface. Fortunately this is a question very easily answered. At some period after the rocks were formed the crust of the earth was broken by volcanic eruptions at various places and times, and turned up, as in the formation of mountains, so that the edges of the various stratifications of the rocks, from those near the surface down to the lowest rocks, are exposed to view. Another means of knowing what the various formations are has been by borings of deep wells. These borings, however, are only confirmatory of what was well known before through the upheavals that are plentiful in all parts of the world. There is abundant evidence that all of the rocks and all of the strata of every name and nature (except perhaps igneous rocks) were originally laid down in water. This is evidenced not only by the stratifications themselves, but by the evidences of sea-life everywhere present in the earth's crust. Before the upheavals in the earth's crust began, the whole surface of the globe was a great ocean of hot water. The substances of which the rocks were formed were undoubtedly held in suspension in the air and in the water, and by a gradual process were deposited in the bottom of the ocean in layers, forming rocks of various kinds, according to the nature of the substance deposited. Gradually the crust of the earth was built up until it acquired a certain thickness; when, either from shrinkage under the crust a great void was formed until it could not sustain its own weight, or the pressure caused by confined gases and molten matter produced an upheaval which broke the crust of the earth outward, causing great wrinkles that we call mountain ranges. Undoubtedly both forces were active in producing these results. When the gases and molten matter had escaped through the rifts in the rocks caused by the upheaval there must have been great voids formed that were filled up by the shrinkage of the earth, causing much irregularity in its surface.

In some places there were enormous elevations, and in others correspondingly deep depressions. The water that before was evenly distributed over the surface of the globe, after the upheavals ran off into the lower levels, filling up the great valleys, forming the seas, and leaving about one-third of the land surface uncovered. It must not be supposed, however, that the appearance of the land was caused by one grand movement or upheaval, but that it has been going on in successive stages through long ages of time. This is clearly evidenced by the rock formations. The deposition of rock strata is still active in the bottoms of the oceans, although not to the same degree as in former times. When the upheaval took place the old stratifications were thrown out of level, but the new ones that were then formed remained in a level position until they were in their turn disturbed by some subsequent upheaval.

The laws of gravitation would tend to precipitate the matter held in suspension by the water straight down to the bottom, toward the center of the earth, so that the plane of these stratifications would tend to be parallel to the surface of the water, that is horizontal, until disturbed. Then they would be tilted in many directions. Hence it will be easily seen why the seams in the rocks, especially in and near mountainous regions, do not lie in a horizontal position after an upheaval, but are found standing at all angles, up to a perpendicular.

Viewed from this standpoint, the solid portion of the old world has gone all to pieces. Wherever there is a chain of mountains it marks a breakage in the earth's crust, and these mountains are not all on the land, but extend under the seas so deeply that they are unable to lift their heads above the surface of the water. The earth is no longer round, except in general outline, but broken up into all sorts of shapes that give the varied conditions of landscape that we find whichever way we turn.

There are but few volcanoes that are active in this age, while in former times they extended for thousands of miles. We still have occasional earthquakes, but undoubtedly they are very slight as compared with those that shook the earth millions of years ago.

If, now, we study the constitution of the earth's crust so far as it has yet been penetrated, we find it divided up into periods called Primary, Secondary, and Tertiary. The primary period reaches down to the line where the lowest forms of animal fossils begin to be found. This is called the "Paleozoic" period, which means the period of "ancient life." From here let us first go downward. Immediately under this lies a stratum of "Metamorphic" rocks. To metamorphose is to change; and metamorphic rocks are those which have been changed by heat or pressure from their original formation. This class of rocks lie on top of what are called "Igneous" rocks, which means that they have been formed by or subjected to heat. All lava-formed rocks are igneous. They are unstratified—not in layers or strata, but in a formless mass—and in this they differ from water-formed rocks.

If there is a molten center to the earth these igneous rocks are undoubtedly the offspring of this great internal furnace. The metamorphic rocks were primarily igneous and are changed somewhat in their structure by the lapse of time. For instance, marble is a metamorphic limestone. The difference between common limestone and marble is in its molecular structure—the way in which its smallest particles are put together. They are both carbonates of lime. But the marble is made up of little crystals and will take a polish, while ordinary uncrystallized limestone will not. The igneous rocks are chiefly granite; and granite is formed of orthoclase-feldspar, mica, and quartz. (The word "orthoclase" means straight fracture, and the orthoclase-feldspar has two lines of cleavage at right angles to each other.) This is the ordinary composition of granite, but there are a great many variations, chiefly as to color and proportions of the ingredients named.

The igneous rocks, then, are the lowest of all; then come the metamorphic rocks; and as before stated, on top of metamorphic rock begins the first evidence of life in its lowest form. The Paleozoic (ancient life) or Primary period is made up of a number of subdivisions. The first and oldest division is called the "Silurian" age, which is underlaid by the metamorphic rocks and overlaid by the rocks of the Devonian period. It is called Silurian, from the name of a kind of fish, fossils of which are found in the rocks of this age, which are distinguished for the absence of land-plant fossils and vertebrate animals.

In the Silurian strata are found limestones, slate, flagstones, shales, etc. On top of the Silurian begins the "Devonian" age, in which is found the old red sandstone, as well as limestone and slate; and here begin to be found the fossils of land-plants. On top of the Devonian lies the "Carboniferous" series, which complete the series of the primary period. In the lower part of this stratum is found carboniferous limestone, which is overlaid by a kind of stone called millstone grit, and on top of this lie the true carboniferous strata or coal-bearing measures. In the coal strata are found the first reptile fossils.

On top of the coal measures begins the Secondary period, or "Mesozoic" (middle life). This period is distinguished for the great development of reptiles, and is called the "age of reptiles." In this age occur the first traces of mammals, and birds, and fishes with bony skeletons. Among plants we find here the first evidence of palms. The formation is chiefly chalk, sandstones, clays, limestone, etc. We now come to the last or "Tertiary" period, which brings us to the top earth. This is chiefly formed of sedimentary rocks—those which have been formed by the settling of sediment, in water.

While we are forced to these general conclusions in regard to the building of the world, and to its subsequent distortion by the series of upheavals that have occurred from time to time, and to the successive "ages" of the layers of rock foundation of its crust, there are many mysteries that remain unsolved and many questions will present themselves to the mind of the reader. One of these questions is, Where was the water and where was the earthy matter before its precipitation? Matter, including water, can exist in the gaseous form, and we only need to assume that there was a core of intense heat, to understand how all the material that we find on the earth and in the earth could have been held in suspension in the gaseous state until the cooling process had reached a stage where the various combinations and recombinations could take place in the great laboratory of nature. If we study the constitution of the sun (and with the modern appliances we are able to do so), we find that it is made up of some and perhaps all of the same materials that are found here on earth. If there is no water existing, in the sun, as water, there are the gases present which would produce it if the conditions were right. And, for all we know, that flaming mass of burning gases may some time go through the same kind of cooling and building up in solids that our earth has experienced.

We thus have what may be called an outline sketch of the process of World-building.