This earth we live on is a planet, and belongs to the solar system of planets. It shines brightly, and appears to other worlds as other planets do to us. It is nearly 25,000 miles in circumference, and has a diameter of a little over 8,000 miles. It is five and a half times denser than water, and weighs about 6,096,000,000,000,000,000,000 tons.

The atmosphere that surrounds this earth is like a shell that is two hundred to three hundred or more miles in thickness. We live at the bottom of an immense ocean of gaseous matter, which envelops everything, and presses upon everything with a force which appears, at first, perfectly incredible, but whose actual amount admits of easy proof. Gravity being, so far as is known, common to all matter, it is natural to expect that gases, being material substances, should be acted upon by the earth’s attraction, as well as solids and liquids. This is really the case, and the result is the weight or pressure of the atmosphere, which is nothing more than the effect of the attraction of the earth on the particles of air. The amount of pressure exerted upon every square inch of the surface of the earth, and the objects thereon, is from fourteen to fifteen pounds. This enormous force is borne without inconvenience by the animal frames, by reason of its perfect uniformity in every direction; and it may be doubled, or even tripled, without inconvenience. An important law which connects the volume occupied by a gas with the pressure made upon it, is expressed by Mariotte in the following manner. This law is usually called Mariotte’s law: “The volume of gas is inversely as the pressure; the density and elastic force are directly as the pressure, and indirectly as the volume.”

This law has been found to be true no matter how rarefied the air.

The atmosphere, like everything else on earth or connected therewith, and like all other planets known, and the earth itself, is composed of elements, as we shall see presently.

The atmospheric air is composed of gases, elementary substances, known by the names of Nitrogen and Oxygen, with variable proportions of carbonic acid and watery vapors, and usually a trace of ammonia. Besides these, there may occasionally be other substances present, depending upon local causes, as the odoriferous principles of plants and the miasmata of marshes, etc., etc.

Nearly three-fourths of the atmosphere is composed of nitrogen, while about one-fourth or less is oxygen. The following is the relative proportion:

Its specific gravity is unity (1), being the standard with which the density of all gaseous substances is compared. It is 814 times lighter than water, and nearly 11,065 times lighter than mercury; 100 cubic inches weigh 31 grains.

Oxygen is necessary to combustion, to the respiration of animals, and to various other natural operations, by all of which that gas is withdrawn from the air. It is obvious that its quantity would gradually diminish, unless the tendency of these causes were counteracted by some compensating process. This, to some considerable extent, is accomplished by vegetation, as it is found that healthy plants, under the influence of the sun’s light, constantly draw carbonic acid from the air, the carbon of which is retained, while the oxygen is returned.

The atmosphere becomes less and less dense from the surface of the earth upwards.

Animals and vegetables exist in this atmosphere. They cannot exist in any other. All living things and beings live on this earth’s crust. Vegetables are fixed to the soil of this earth, while animals move freely upon it.

The earth’s crust.—Sir Charles Lyell speaking of this earth’s crust says: “By the ‘earth’s crust’ is meant that small portion of the surface of our planet which is accessible to human observation, or on which we are enabled to reason by observations made at or near the surface. These reasonings may extend to a depth of several miles, perhaps ten miles; and even then it may be said that such a thickness is no more than 1/400? part of the distance from the surface to the center. The remark is just, but although the dimensions of such a crust are, in truth, insignificant when compared with the entire globe, yet they are vast and of magnificent extent in relation to man and to the other organic beings which people our globe. Referring to this standard of magnitude, the geologist may admire the ample limits of his domain, and admit at the same time that not only the exterior of the planet, but the entire earth, is but an atom in the midst of the countless worlds surveyed by the astronomer.

“The solid part of this earth consists of distinct substances, such as clay, chalk, sand, limestone, coal, slate, granite, and the like. It has been imagined that the various deposits on the earth’s surface were created in their present form and in their present position. On the contrary, it has been shown that they have acquired their actual configuration and condition gradually, under a variety of circumstances, and at successive periods, during each of which distinct races of living beings have flourished on the land and in the waters, the remains of these creatures still lying buried in the crust of the earth.

“The materials of this crust are not thrown together confusedly; but distinct mineral masses called rock are found to occupy definite spaces and to exhibit a certain order of arrangement. These rocks are divided into four great classes by reference to their different origin, or in other words by reference to the different circumstances and causes by which they have been produced.

“The first two divisions, which will at once be understood as natural, are the aqueous and volcanic, or the products of water and those of igneous action at or near the surface.… The aqueous rocks, sometimes called sedimentary or fossiliferous, cover a larger part of the earth’s surface than any other. These rocks are stratified, or divided into distinct layers or strata; these strata have been generally spread out by the action of water, like what we daily see taking place near the mouth of rivers or on the land during a temporary inundation.

“The remains of animals, especially of aquatic species, are found almost everywhere, imbedded in stratified rocks; and sometimes, in the case of limestone, they are in such abundance as to constitute the entire mass of rock itself. Shells and corals are the most frequent, and with them are often associated the bones and teeth of fishes, fragments of wood, impressions of leaves, and other organic substances.

“When geology was first cultivated, it was a general belief that those marine shells and other fossils were the effects and proofs of the deluge of Noah; but all those who have carefully investigated the phenomena have rejected this doctrine. A transient flood might be supposed to leave behind it, here and there upon the surface, scattered heaps of mud and sand and shingle, with shells confusedly intermixed; but the strata containing fossils are not superficial deposits, and do not simply cover the earth, but constitute the entire mass of mountains. Ample proof of these reiterated revelations is given, and it will be seen that many distinct sets of sedimentary strata, each several hundreds or thousands of feet thick, are piled one upon the other in the earth’s crust, each containing peculiar fossil animals and plants, which are distinguishable, with few exceptions, from species now living. The mass of some of these strata consists almost entirely of corals, others are made up of shells, others of plants turned into coal, while some are without fossil.

“Volcanic rocks are those which have been produced at or near the surface, whether in ancient or modern times, not by water, but by the action of fire or subterranean heat. These rocks are for the most part unstratified, and are devoid of fossils.

“There are two other divisions of rock, called Plutonic rocks, granite, etc., and Metamorphic, or stratified crystalline rocks. The members of both these divisions of rocks agree in being highly crystalline and destitute of organic remains.

“The composition of the aqueous rocks, mineral composition of strata: These may be said to belong principally to three divisions, as follows:

“1. Arenaceous or siliceous rocks. Beds of loose sand frequently met with, of which the grains consist entirely of silex, which term comprehends all purely siliceous minerals, as quartz and common flint. Quartz is silex in its purest form; flint usually contains some admixture of alumina and the oxide of iron. Silica is the mineral used in the manufacture of glass, mixed with a little potassium oxide and lime, or lead, etc.

“2. Argillaceous rock. A mixture of silex or flint with a large proportion, usually about one-fourth, of alumina or argil; but in common language, any earth which possesses sufficient ductility, when kneaded up with water, to be fashioned like paste by the hand or by the potter’s lathe, is called clay. Such clays vary greatly in their composition. They are, in general, nothing more than mud derived from the decomposition or wearing down of various rocks. The purest clay in nature is porcelain clay or kaolin, which results from the decomposition of a rock composed of feldspar and quartz, and it is almost always mixed with quartz. (The kaolin of China consists of 71.15 parts of silex, 15.86 of alumina, 1.92 of lime, and 6.73 of water.)… One general character of all argillaceous rocks is to give out a peculiar, earthy odor when breathed upon, which is a test of the presence of alumina.

“3. Calcareous Rocks. These consist mainly of chalk—lime and carbonic acid. Shells and corals also are formed of the same elements, with the addition of animal matter. Any limestone which is sufficiently hard to take a fine polish is called marble. Many of these are fossiliferous; but statuary marble, which is also called saccharine limestone, as having a texture resembling that of loaf-sugar, is devoid of fossil. Siliceous limestone is an intimate mixture of carbonate of lime and flint, and is harder in proportion as the flinty matter predominates. Marl slate bears the same relation to marl which shale bears to clay, being calcareous shale. Magnesian limestone is composed of carbonate of lime and carbonate of magnesia; the proportion of the latter amounting in some cases to nearly one-half. It effervesces much more slowly and feebly with acid than common limestone. Gypsum is a rock composed of sulphuric acid, lime, and water. It is usually a soft whitish-yellow rock, with a texture resembling loaf-sugar, but sometimes it is entirely composed of lenticular crystals. Alabaster is a granular and compact variety of gypsum found in masses large enough to be used in sculpture and architecture. It is sometimes a pure snow-white substance. It is a softer stone than marble and more easily wrought.”

When geologists examine the earth’s crust, they usually commence with the surface on which we live, and search downwards as far as possible. Lyell constructed a tabular view of the fossiliferous strata.

It must be borne in mind that we have no other methods of ascertaining the truth than by close observation, making diligent search, in order to discover what this earth’s crust is made of. We have no supernatural facilities to give us information, and we are very certain there never were any. What information we are reckoned to have, handed down by our antiquated barbarian forefathers, is of a different nature. It refers—briefly stated—to the conduct of Man, the manner in which he shall act as an individual, or collectively as a community; including a great number of what are considered now theatrical or mountebank ceremonies, fancy customs, sacrifices, and a repetition of certain phrases, ordinarily called prayers, accompanied by illustrative images and pictures, and movements of body—fantastic symbols and devices created and prescribed by man.

Having no other means of ascertaining facts, man was naturally compelled to search for testimony in the earth’s crust—to discover what it is composed of; the kind of material; how it was formed; the time it took to form; the period that elapsed between formations; how the layers or strata were superposed one upon another; what substances were found in them; where organic life was first found; what it consisted of; when man first appeared. By examining this table we get a glimpse of the true state of things. This shows the order of superposition, or chronological succession, of the principal European groups:

I. Post-Tertiary. A. Post-Pliocene.

Periods and Groups.

1. Recent. Peat mosses, shell marls, with bones of land animals, human remains and works of art. Newer parts of modern deltas and coral reefs.

2. Post-Pliocene. Clay, marl, volcanic trap. All the shell of living specimens. No human remains or works of art. Bones of quadrupeds, partly of extinct species.

II. Tertiary. B. Pliocene.

3. Newer Pliocene. Boulder formation. Cavern formation, or Pleistocene. Three-fourths of fossil shells of extinct species. A majority of the mammals extinct; but the genera corresponding with those now surviving in the same great geographical and zoological provinces. Icebergs frequent in the seas; glaciers on hills of moderate height.

4. Older Pliocene. A third or more of the species of mollusca extinct. Nearly, if not all, the mammalia extinct.

C. Miocene.

5. Miocene. About two-thirds of the species of shells extinct. All the mammalia extinct.

D. Eocene.

III. Secondary. E. Cretaceous—Upper.

9. Maestricht beds. Yellowish-white limestone. Large marine saurians, etc.

10. Upper white chalk. Marine limestone composed in part of decomposed corals.

11. Lower white chalk.

12. Upper green sand.

13. Gault. Dark-blue marl at base of chalk escarpment. Numerous extinct genera—conchiferous cephalopoda, etc.

14. Lower green sand. Species of shells, etc., nearly all distinct from those of Upper Cretaceous.

F. Wealden.

15. Weald clay, of fresh-water origin. Shells of Pulmoniferous mollusca.

16. Hastings sand. Fresh water. Reptiles of, etc.

17. Purbeck beds. Limestone, calcareous slate, etc. Roots of trees; plants, etc.

G. OÖlite.

18. Upper OÖlite. Portland building-stone, sand.

19. Middle OÖlite. Oxford clay, dark-blue clay. Large saurians.

20. Lower OÖlite. Preponderance of ganoid fish. Plants chiefly cycads, conifers, and ferns.

H. Lias.

21. Argillaceous limestone, marl clay. Mollusca, reptiles, and fish analogous to the OÖlitic.

I. Trias.

22. Upper Trias. Red, gray, green, blue, and white marls, and sandstone, with gypsum. Batrachian reptiles.

23. Middle Trias. Compact grayish limestone, with beds of muschelkalk, of dolomite and gypsum.

24. Lower Trias. Plants different for the most part.

IV. Primary. J. Permian.

25. Upper Permian. Yellow magnesian limestone. Organic remains both animal and vegetable, more allied to primary than to secondary period.

26. Lower Permian. Marl slate. Thecodont saurians, heterocercal fish, etc.

K. Carboniferous.

27. Coal measures. Great thickness of strata of fluvio-marine origin, with beds of coal of vegetable origin, based on soils retaining roots of trees. Oldest of known reptiles. Sauroid fish.

28. Mountain. Carboniferous or mountain limestone. Limestone with marine shells and corals, etc.

L. Devonian.

29. Upper Devonian. Yellow sandstone, paving and roofing stone. Tribe of fish with hard coverings. No reptiles yet known.

30. Lower Devonian. Gray sandstone.

M. Silurian.

31. Upper Silurian. Tilestone. Oldest fossil fish yet discovered. Trilobites, etc.

32. Lower Silurian. Caradoc sandstone, etc. No land plants yet known. Footprints of tortoise, etc.

33. Upper and Lower Cambrian.

The precise chemical action upon the elements composing these various geological formations at different remote periods, is no doubt difficult to ascertain. That there always has been some chemical action going on, and that it is continually going on, is certain. How and to what extent we can judge only from the experience of actual observation in the laboratory.

Mr. Crale remarks: “The whole surface of the land is exposed to chemical action of the air, and of the rainwater with its dissolved carbonic acid, and in colder countries the frost. The disintegrated matter is carried down the slopes during heavy rain; and, to a greater extent than might be supposed, especially in arid districts, by the wind; it is then transported by the streams and rivers, which when rapid deepen their channels and triturate the fragments.” Darwin says: “If the theory be true” (speaking of the time elapsed since the Cambrian lowest formation) “it is indisputable that before the lowest Cambrian stratum was deposited, long periods elapsed, as long as, or probably far longer than, the whole interval from the Cambrian age to the present day; that during these vast periods, the world swarmed with living creatures. Here we encounter a formidable objection; for it seems doubtful whether the earth, in a fit state for the habitation of living creatures, has lasted long enough. Sir W. Thompson concludes that the consolidation of the crust can hardly have occurred less than 20 or more than 400 million years ago, but probably not less than 98 or more than 200 millions of years. These very wide limits show how doubtful the data are; and other elements may have hereafter to be introduced into the problem. Mr. Crale estimates that about 60 million years have elapsed since the Cambrian period, but this, judging from the small amount of organic change since the commencement of the glacial epoch, appears a very short time for the many and great mutations of life, which have certainly occurred since the Cambrian formation; and the previous 140 millions of years can hardly be considered as sufficient for the development of the varied forms of life which already existed during the Cambrian period.”

It seems almost impossible for an ordinary mind to grasp the magnitude of the figures, the span of life being so short. Yet some idea may be formed when we compare the age of this earth’s crust formation, the hundreds of thousands of years that passed in the evolution of man, and the brief space of time that has elapsed since he has become enabled to give an account of himself.

As regards the thickness of the earth’s crust, Professor Ramsey has given the maximum thickness, from actual measurement in most cases, of the successive formations in different parts of Great Britain; and this is the result:

making altogether 72,584 feet; that is, very nearly thirteen and three-quarters British miles. BÜchner in his work on “Force and Matter” states: “The so-called coal formation alone required, according to Bischoff, 1,000,177 years; according to Chevandier’s calculation, 672,788 years. The Tertiary strata required for their development about 350,000 years; and before the originally incandescent earth could cool down from a temperature of 2,000 degrees to 200, there must, according to Bischoff’s calculation, have elapsed a period of 350,000,000 years. Valger calculates that the time required for the deposit of the strata known to us must at least have amounted to 648,000,000 years. I quote these figures simply to show how difficult it is, and the labor required, to form even a proximate idea as to the period of time that must have elapsed for the formation of the various strata known.

That all animals were not created at once is certain beyond all cavil and dispute. The development of the various forms of life was an exceeding slow process, and lasted very many thousand centuries. That the earth’s crust was not at certain stages of formation in a fit condition either to receive or to maintain the higher types of animal life, is well known. And we know that man’s remains are found only in the uppermost surface of the earth’s crust. Max MÜller says in his “Testimony of the Rocks”: “It was not until the earlier ages of the OÖlite system had passed away, that the class of Reptiles received its fullest development. And certainly very wonderful was the development which it did then receive. Reptiles became everywhere the lords and masters of the lower world. When any class of air-breathing vertebrates is very largely developed, we find it taking possession of all three terrestrial elements—earth, air, and water. Last of all, the true placental mammals appear, and thus, tried by the test of perfect reproduction, the great vertebral division receives its full development.” Agassiz’s “Principles of Zoology” says: “We distinguish four ages of nature, comprehending the great geological divisions, namely:

“1. The Primary, or Paleozoic age, comprising the lower Silurian, the upper Silurian, and the Devonian. During this age there were no air-breathing animals. The fishes were masters of creation. We may therefore call it the Reign of Fishes.

“2. The Secondary age, comprising the Carboniferous, the Trias, the OÖlite, and the Cretaceous formations. This is the epoch in which air-breathing animals first appear. The Reptiles predominated over the other classes, and we may therefore call it the ‘Reign of Reptiles.’

“3. The Tertiary age, comprising the Tertiary formation. During this age terrestrial mammals of great size abound. This is the Reign of Mammals.

“4. The Modern age, characterized by the appearance of the most perfect of created beings.”

The majority of mankind trouble themselves but little whether progress is made in any one of the branches of science or not. Man has no time to think seriously of anything except to provide food for his family. The priest does his thinking, and he is made to contribute part of his labor to support the holy man who does the thinking for him. All he knows is that his soul or his spirit, his hereafter, and his God are well cared for, and he pays for it. Yet every man ought to understand that all his rights, civil and political—all the freedom he enjoys—he has to thank science for procuring and securing.

“Shall it be seriously objected to the application of the sciences to philosophical problems that its results are not agreeable? That the truth is not always agreeable, nor always consolatory, nor always religious, nor always acceptable, is as well known as the old experience of the almost total absence of reward, either external or internal, provided for its exemplars. What this or that man may understand by a governing reason, an absolute power, a universal soul, a personal God … is his own affair. The theologians, with their articles of faith, must be left to themselves; so of the naturalists with their science; they both proceed by different routes.… The same bloody hatred with which science was once persecuted by religious fanaticism would revive now, and with it the Inquisition and Auto-da-fÉ, and all the horrors with which a refined zealotism has tortured humanity would be resorted to, to satisfy the wishes of the theological cutthroats. A man in advance of his age beholds the struggle of the contending parties from a high point of view, and sees in the eccentricities of this contest merely the natural and necessary expression of the opposing elements which agitate our time. No one can doubt that truth will finally emerge the victor. It certainly will not be long before the battle becomes general. Is the victory doubtful? The struggle is unequal; the opponents cannot stand against the trenchant arm of physical and physiological Materialism, which fights with facts, that everyone can comprehend, while the opponents fight with suppositions and presumptions” (BÜchner).

“Science and faith exclude each other” (Virchow).

Fools still cling to faith; wise men find the truth in science.

Note.—Baily’s “History of Astronomy,” Part I, page 31, § 124, and Part II, pp. 33, 39, maintains that India has existed as a nation, as the records show, 4,320,000 years. The Indians divide this time into four principal periods: First period, that of innocence or simplicity, 1,728,000 years; second period, 276,000; the third period, 864,000; and the ages of misfortune about 422,000—Cali-yon-gan period. Similar statements are made by Cicero (“De Divinat,” I, 19), concerning the Chaldeans: “Condemnemus, inquam, hos aut stultitiÆ aut vanitatis aut imprudentiÆ qui 470 millia annorum ut ipsi dicunt monumentis comprehensa continent.”