THE EARTH.

The Earth, considered as one of those spheres which circulate round the sun amidst the wide expanse of the firmanent, holds but an insignificant position among them, especially when compared with those great and magnificent orbs, Jupiter and Saturn; but, in another point of view, as the dwelling-place of all the animated beings, vegetables, and minerals, with which we have any practical knowledge, it holds to us a position in creation far above all the others.

It is upon the surface of this our earth that we behold in detail those wonders of the Great Creator's hands,which must fill all who contemplate and study them with enlarged ideas of His wisdom, goodness, and power. We see the millions of stars sparkling in the abyss of space, and our minds are so formed that we can measure and gauge their distances and rates of travelling, their orbits and their sizes, their weights, and the powers with which they attract and influence each other; but we only contemplate a star as one bright and beautiful object worthy to be one of the gems which the Almighty has set in His crown of glory, or a lamp to light the halls of His infinite habitation, but we still contemplate it as a single object; while on the surface of the earth our Maker has permitted us to roam and search out by what benevolent contrivances He has suited all things to the comfort and welfare of His creatures. How His mercy and goodness are extended amply to the most minute animalcule as well as to man, and how His powers of construction are to be found in the most minute objects which the microscope can display, as perfect as in the largest creature we behold. It is here upon our earth that we perceive how the structure and functions of all creatures are regulated and controlled by the unerring laws which He has created, over which laws the creatures have no control, and which if duly regarded and used according to the faculties each has been gifted with, will return the greatest joy and happiness their several natures are capable of, and secure all that perfection of operation which their mechanical frames are suited to perform; but before any description of the organised beings which dwell on the earth can be given, it will be proper to enter into a description of the earth itself, to see what sort of place God has provided for them, and how through succeeding cycles of time He has gradually perfected and prepared it for the reception of His last great work, Man.

It is only a few miles below the surface of the earth that man has been able to penetrate and examine, but reason comes to assist him where examination fails, and it would have been but a few hundred yards only that his labours could have extended had it not been that parts, which are generally situated miles below the surface, are occasionally foundat or even raised above it, by some disturbing cause which operated in times far back; so that man is able to examine on the surface parts which he could scarcely dig down to.

The whole of the earth, its inhabitants, the air which surrounds it, the waters upon its surface, and its vegetable products, are composed of certain substances called elements, combined and united in certain numbers and proportions. The following is a list of all known:—

METALLIC ELEMENTS.Aluminium13.7Nickel29.6Antimony12.9Niobium*Arsenic75Norium*Barium68.5Osmium99.6Bismuth21.3Palladium53.3Cadmium56Pelopium*Calcium20Platinum98.7Cerium47Potassium39.2Chromium26.7Rhodium52.2Cobalt29.5Ruthenium52.2Copper31.7Silicon21.3Didymium*Silver108.1Donarium*Sodium23Erbium*Strontium43.8Glucinium*Tantalium184Gold197Tellurium64.2Ilmenium*Terbinum*Iridium99Thorium59.6Iron28Tin59Lanthanium*Titanium25Lead103.7Tungsten95Lithium6.5Uranium60Magnesium12.2Vanadium68.6Manganese27.6Yttrium32.2Mercury100Zinc32.6Molybdenum46Zirconium22.4

NON-METALLIC ELEMENTS.Boron10.9Iodine127.1Bromine80Nitrogen14Carbon6Oxygen8Chlorine35Phosphorus32Fluorine18.9Sulphur16Hydrogen1Selenium39.5

By this list it will be perceived that the greatest number of the elements are metals, but most of these are very rare and met with but in certain localities, making up but a very insignificant part of the earth's surface, while others (never found in nature, as metals) in combination with oxygen forming "earths" compose the greater part of its bulk. But of all the elements, oxygen (a gas) is the most widely diffused, and constitutes rather more than one half of the whole earth, thus it forms 1/5th of the air, 9/10ths of the water, of the various earths and rocks about 1/2, and in all organised beings about 3/4.

Of the metallic elements, those which form the greater bulk of the earth are—

Silicon.Aluminium.Calcium.Magnesium.Potassium.Sodium.

These never exist in nature as metals, but combined with oxygen forming the following earths and alkalies:—

Silica }Alumina }Earths.Lime }Magnesia }Potassa }Alkalies.Soda }

These four "earths" form about eighty-five per cent. of the whole bulk of this globe, the remainder being made up of water (composed of eight parts oxygen and one part hydrogen), of "salt," both as rock or crystal-salt, and dissolved in the water of the sea, of the ores of different metals (metals in union with oxygen, sulphur, &c.), and of the remains of former vegetation, existing as coal.

Silica is composed of 21.3 parts of silicon with 24 of oxygen, it is that earth which constitutes a great part of almost every soil, and forms sand, sandstone, and flint, it enters largely also into the formation of granite and the other primitive rocks; when pure it is called "quartz" or "rock-crystal" and is often found in large and beautiful masses. Silica, in different forms, contaminated and coloured by different metallic oxides, &c., forms that class of stonesknown as "agate," "Scotch pebble," "carnelian," &c., and in the form of flint is found nearly pure, forming "nodules" or rounded masses lying in layers in the chalk cliffs on our coasts, the origin of these nodules of flint is very obscure, but they are by many attributed to the petrifaction of sponges, &c., the general form of which they often retain as well as their internal structure, which may be seen when viewed in thin slices by means of the microscope. Pure silica is a white insoluble powder, and is much used by the makers of porcelain to mix with their other ingredients.

Alumina consists of 41.1 parts of aluminium in combination with 24 parts of oxygen, it is the earth which forms the basis of all clays, loams, and slates, it is in its pure state perfectly white but in most clays is coloured brown or blueish by oxide of iron, many of our most beautiful gems, as the ruby, sapphire, and emerald, consist chiefly of crystallised alumina coloured by oxide of iron, chromium, &c., this earth like silica enters largely into the composition of the primitive rocks.

Lime is another of the earths which form a great part of all soils; it consists of 20 parts calcium with 8 of oxygen. Unlike the two preceding earths, it exists only in union with some acid. When united to carbonic acid it forms limestone, chalk, marble, &c., and when in a crystallised state "Iceland spar." The various kinds of limestone are largely used as building-stones, and any of them when burnt yields lime or "quick-lime" as it is generally called, which is capable of uniting with a certain portion of water, giving out a considerable amount of heat during the combination. Lime is often found in union with sulphuric acid, forming gypsum or Plaster of Paris, in combination with phosphoric acid it forms the basis or earthy part of the bones of animals, and is found in some of the tissues of plants.

Potassa consists of 39.2 parts potassium in union with 8 oxygen, it constitutes about 12 per cent. of the granites and basalts (primitive rocks) in union with silica and alumina, it is also found in the fluids of many vegetables in union with carbonic, oxalic, and other acids.

Soda consists of twenty-three parts sodium with eight oxygen, it however does not exist in this form in nature, but in union with chlorine instead of oxygen, constituting chloride of sodium or common salt, this substance forms strata of considerable extent in some localities and being soluble has no doubt been washed out by the rains from many other places and has thus communicated saltness to the waters of the ocean. The other metallic elements exist chiefly in those forms of earth called "ores" being metals in union with oxygen, sulphur, &c., or are found in the metallic state, as gold, platinum, &c., it is from these ores that most of our useful metals are procured by the process called smelting, as in the case of iron, copper, lead, tin, &c. All the substances known result from the combinations of the elements, but these elements do not chemically combine in all proportions, but in certain definite quantities only; these quantities or proportions are signified by the numbers attached to each element in the list given,1and the union of these substances must be in the proportion of these numbers (or multiples of them) only, all superfluity of the substances combined remaining in a state of mere mechanical mixture. For example, if six parts of carbon (charcoal) made red-hot be plunged into a jar containing twenty parts of oxygen, it will unite with sixteen parts only of the oxygen (a multiple of eight), and form twenty-two parts of carbonic acid, the extra four parts of oxygen still remaining as oxygen mixed with the carbonic acid; and if into this carbonic acid twenty parts of lime be put, it will unite with the twenty-two of carbonic acid, forming forty-two of carbonate of lime, still leaving the four parts of oxygen untouched. Had forty parts of lime been put into the mixture, instead of twenty, still only forty-two of carbonate of lime would have been formed, and the other twenty parts (like the four of oxygen) being superfluous, would still have remained as lime, mixed with the carbonate of lime. These combining quantities are called the "equivalents" of the substances.

1See the list of the elements atpage 45; those which are distinguished by an asterisk, are elements of which the "equivalents" are not known.

Upon examining various portions of the earth's surface, they will be found to differ in character from each other; in one place perhaps sandy soil will be found, in another, hard rock, in a third, clay, in a fourth, chalk, and so on. Now, if this examination were carried no further, it might well be presumed that each of these kinds of soil were continued downwards into the earth for an indefinite distance, but upon digging (as in sinking a shaft or well) it is found that the stratum of soil upon the surface is soon passed through, that others in succession present themselves and that this succession of strata is not a matter of chance, but (with certain restrictions) follows in invariable order. It is true some strata are occasionally not present, and that others replace them; but yet (taken altogether) there is the same order of succession everywhere found. The following diagram (fig. 1) gives the section of these strata from the earth's surface to the granite which is the lowest of all formations and through which no one has ever penetrated. The figures give an approximation to their average thickness in feet. These strata do not all run in a direction parallel to the surface of the earth, or else it would result that the surface would everywhere be made up of the highest, but they have been contorted and heaved up into mounds or depressed; and the granite has often been pushed upwards, carrying with it all the upper strata to a certain extent, at last thrusting quite through them all and presenting itself above the surface, forming in this way the tops of many very high mountains, Mont Blanc for instance. Such a mountain if cleft from the summit to the base would present a section similar to that shown in fig. 2, and thus it occurs (contrary to what would at first thought be supposed) that the highest ground is generally formed of the lowest strata, while the valleys are nearly always covered with the latest formations, which is partly owing to the elevating process before alluded to, and partly to the winds, rains, &c., tending to carry away and wash down every kind of soil from the upper ground and deposit it in the lower.

FIG. 1.—DIAGRAM SHOWING THE POSITIONS AND RELATIVE THICKNESSES OF THE STRATA.

FIG. 2.

FIG. 3.

FIG. 4.

FIG. 5.

Fig. 3 represents strata in a state called by geologists "conformable," which name is applied when the strata follow their natural or regular succession, whether this retains its horizontal position, or, as in fig. 4, assumes a position more or less vertical, which frequently happens from the subsidence of one part or the elevation of another; but they are sometimes found in the state represented in fig. 5, and in which they are said to be "unconformable." Such strata after having been tilted out of the horizontal havehad other strata deposited upon them, which again may be more or less contorted from the same causes. The regularity of strata is often interrupted by what are called "faults" or "dykes," which have arisen from some part of the earth sinking down or another part being raised up, producing a fracture through all the strata and causing those on either side of this fault or fracture to occupy a situation not corresponding to those on the opposite, as in fig. 6, but yet to be found at a higher or lower elevation, and it is nearly always found that these strata are raised on that side to which the line of fracture inclines, as in the figure. These faults are often sources of great annoyance to the miner, who finds a sudden termination to the seam of coal or ore that he is working. The cracks are generally filled with some primitive rock, as basalt, rising from beneath while in a liquid state and filling up the interstices; it will often happen that the faults thus filled will have veins of the same rock branching out and not only filling up cracks but forcing its way between the various strata, thus interposing a stratum of basalt quite out of its proper position and altering, by the effects of the heat communicated, the character of the strata in juxtaposition; this is shown in fig. 7.

FIG. 6.

Upon a close examination of the various strata which form the crust of the earth, it is found that each has its own peculiar character; some have resulted from the accumulation of matters deposited at the bottom of ancient seas, others in the beds of rivers or fresh-water lakes, or again others (as the coal formation) from the accumulation of vegetable matters; further, these strata do not only differ in structure and composition, but also in the remains ofanimals and plants found in them; for there is scarcely any kind of soil (above the primary rocks) in which abundant remains of these have not been found. It will now be proper to give a description of them in succession, beginning at the lowest or primary,granite.

FIG. 7.

This appears to be the result of the cooling and crystallisation of that molten mass which many circumstances (hereafter to be mentioned) point out as making up the great body of the earth. Granite differs, in various places, in colour and quality (the varieties are known as "sienite," "porphyry," "greenstone," &c.), but still retains its own distinctive characters; it is a hard, crystalline rock, consisting of "felspar," "mica," and "quartz," in separate crystals, but mechanically blended; its chemical composition as a whole is silica, alumina, and potassa, with small quantities of lime and oxide of iron. This granite is met with everywhere, if the outer crust of the earth be penetrated to a sufficient depth; it however frequently exists on the surface, having no strata below it, and in some places overlies other strata—this, and the fact that cracks and crevices of some of the lower strata are filled up with granite, which could only have taken place while it was in a liquid state, as in fig. 8, together with evidences of the effects of calcination, and other changes producible only by extreme heat, all around those parts and in the strata immediately overlaying the granite, point out that it was once in a state of fusion.

Above the granite formation, in many places, especially in Norway and Sweden, there is a stratum of rock calledgneiss, which consists of the same ingredients as granite in a slightly altered form. Granite will often pass into gneiss gradually, and this again into those slaty formations which rest upon it and come next in the series. These consist of mica-slate, hornblend-slate, and chlorite-slate or schist, a name given to all those rocks of a slaty structure which have a cleavage or capability of being cleft into thin laminæ or slices (hence their applicability to the purposes of building, forming excellent roofing materials, &c.).

FIG. 8.

All these rocks have received the name of "primary," they have no appearance of being stratified or deposited in layers, which appearance seems to be in all cases the result of having at some time been suspended in water and thence deposited gradually as mud, sand, &c., time, pressure, and heat having afterwards altered their consistence. All these consist of the earths described as composing granite, but combined in different proportions. Above these rocks there is a formation of a totally different composition, namely crystalline limestone, commonly known as marble; this consists wholly of carbonate of lime or lime in union with carbonic acid, and its crystalline state appears to have been produced by long-continued heat and pressure. This limestone is by many ranked amongst the primary rocks, although it differs so entirely in its composition which exactly resembles a formation presently to be described (the chalk); however, if this be classed with the primary rocks, then it may be fairly said that all above have resulted from their disintegration and reunion in different forms, by the action of water and vital forces of different kinds. The state ofthe earth at the close of this the "primary period" may now be considered.

The early history of our globe forms one of the great problems of geology, but there is evidence enough upon which to form conclusions and show that the earth had undergone some great and varied changes embracing immense periods of time, and if the sciences of astronomy, chemistry, mathematics, &c., be brought in to assist the inquiry, some plain facts become evident. Astronomy shows us orbs circulating round the sun (the planets), strictly analogous to our earth, and furnishes us with their densities; these are found to be various, ranging from about six times the density of water to half its density. The planets appear to be at different stages of condensation, and it is not unreasonable to suppose that our earth was once of no greater density than the lightest of them. The inner ring of Saturn is probably in a liquid state, for it is transparent. The substance of which comets are composed is a vapour, so rare and thin that it cannot be compared in density to our atmosphere even, and yet these comets preserve their identity, circulating through immense realms of space with prodigious rapidity. Thus astronomy presents analogies in favour of the supposition that the earth was once gaseous, or at all events of much less density than at present; but mathematical inquiries go much further, and furnish almost proof that the earth was once (if not now) in a liquid state, for the exact form which a liquid ball would assume upon rotating at the rate which the earth does, is exactly that which the globe is found by measurement to possess.

Chemistry has ascertained that the heat of the earth is far greater than any tract of the heavens through which it passes; that this heat could not have been communicated by the sun's rays, for had it been so the surface would be hotter than the interior, the very reverse of which is found to be the fact, and the deeper we go down the higher the temperature is. Chemistry shows further that this heat can be completely accounted for by the condensation and solidification of the earth itself; for the condensation of allgases into liquids, and of liquids into solids, causes a very large portion of latent caloric to become sensible, for example, any quantity of a gas at 60 deg. suddenly reduced to a smaller bulk, would have a temperature higher than 60 deg. A little contrivance has long been in use for obtaining fire by this process, consisting of a cylinder and piston, the rod of which if struck down sets fire to a piece of German-tinder. It is probable that all fire, and every alteration of temperature, are due to this one cause alone.

Now assuming it as a fact that the earth was once in a gaseous state, and that the atoms of this gas or vapour exerted (as they must have done) an attraction towards each other, the result would be that they would press immensely upon those parts towards the centre and cause them to solidify. This act of solidification would produce such an intense heat that the solid would be expanded and fused into a liquid, this continuing until all the more condensible matters had become liquid, the earth would assume its spheroidal form from its rotation, be surrounded by an atmosphere of the least easily condensible substance, nitrogen, together with all the oxygen not wanted to combine with the metallic vapour and form earth. This globe with its atmosphere continuing to roll through the cold regions of space, would gradually lose the heat from its outer part by radiation. A film of cooled and condensed earthy matter would begin to form on the surface by crystallisation, and then would commence all those grand phenomena which it is the province of the geologist to study and explain. This crust consisted of the first-formed granite which (from inequality of contraction in the bulk of the earth) was broken up into fragments and perhaps partly re-dissolved again and again in some places, as it chanced that these contractions were more or less irregular. The result of this crushing and crumbling-up is seen in the coarser parts of the gneiss, called "Grauwacke," which consist of angular fragments of granite more or less imbedded in a cement of the same substance. This could not have been produced by water, as the surface must have been too hot for it to have existed on the earth in any other form than the most highlyrarefied steam combined with the atmosphere, and in all probability partly condensed in the upper regions, forming a continuous strata of clouds, or rather water, through which the sun could hardly be seen or its light penetrate, and such a state of things exists at this present time in the planet Jupiter. How beautifully does this coincide with the Mosaic account, "The earth was without form and void, and darkness was upon the face of the earth."

The surface of the earth at this time can be well understood by any one who will take the pains to evaporate any saline solution in a capsule till it is about to crystallise, and observe attentively the pellicle of salt as it forms on the surface; first a partial film will show itself in a few places, floating about and joining with others, then when nearly the whole surface is coated, it will break up in some places and sink into the liquid beneath, another pellicle will form and join with the remains of the first, and as this thickens it will push up ridges and inequalities of the surface from openings and fissures in which little jets of steam and fluid will escape; these little ridges are chains of mountains, the little jets of steam those volcanic eruptions which were at that period so frequent; the surface of the capsule is the surface of the earth, and the five minutes which the observer has contemplated it, a million years.

The next effect of the cooling of the earth would be the gradual condensation of the vapour of water with which it was surrounded; this falling upon the earth formed seas and oceans, leaving only the higher portions exposed above its level. The clearing-up of the dense dark clouds for the first time let in to the earth's surface the glorious and vivifying rays of the sun, and this great effect possibly accords with the earliest record in the Bible of the acts of creation—"And God said, let there be light, and there was light."

FIG. 9—STALAGMITE. FIG. 10.—TEREBRATULA.

The earth being chiefly covered with water, and the air partly freed from watery vapour, then commenced the great creation of organised beings. The air, although to a certain extent, free from vapour, must yet have contained an enormous amount of carbonic acid; this, being less easily condensed than any of the matters which had gone throughthat process, would still remain there as a gas, and the effect of this superabundance would be to saturate all the water covering the earth with it; this solution of carbonic acid, being capable of dissolving lime, would (as it percolated and rushed in currents through the rocks and inequalities of the surface) become converted into a solution of percarbonate of lime, taking up a large quantity of this earth from the broken-up granite, &c., then this carbonate of lime would be deposited at the bottom of the water in one of two ways—either from pressure, diminution of carbonic acid in the air, and heat of the surface, it crystallised at the bottom in the form of marble (that the water does thus become saturated with carbonic acid and take up lime, is constantly shown by the stalagmites which form on the floors of caverns, where the water thus loaded with percarbonate of lime, evaporating, deposits gradually the carbonate in all sorts of fantastic shapes, as in fig. 9), or the myriads of crinoidians and brachiopodous molluscs (fig. 10) which were about this time created, absorbed it into their systems and at their death deposited their shells, which are made of this earth, at the bottom of the sea; these shells, accumulating through ages into strata, became hardened and partly crystallised by heat, thus forming the limestones, which were the first containing carbonate of lime. That such a collection, from such causes, isquite possible, will be presently shown in describing the chalk formation.

Ages of comparative quiet now appear to have succeeded the first great contraction of the earth's crust, probably millions of years, during which time the tides and currents of the ocean had to wash and wear down all the thousands of projecting rocks or inequalities and dissolve (as before described) all the lime, depositing the sand and clay in those immense strata which form the "transition series;" this appears to have taken place over nearly the whole world at that time, and ages upon ages must have elapsed to form such deposits as the sandstone, claystone, and limestone, in alternation, forming the "Llandilo," "Caradoc," and "Wenlock" strata, more than a mile in thickness; these are by some geologists reckoned among the primary series (by some called the "transition rocks"), and in England form the "Cambrian" and "Silurian" systems.

FIG. 11—TRILOBITE.

In these strata the remains of organised beings are first found, consisting of zoophytes, crustacea (chiefly Trilobites, fig. 11), nautili, crinoidii (stone lilies), and a few ganoid (plate-covered) fishes; these lower forms of animal life in some parts abound in the most prodigious numbers. There must, of course, have been vegetables of some kind previously formed to constitute nourishment for these animals, but scarcely any remains of such exist, except in a few localities.

The Trilobites were amongst the first creatures inhabiting our globe, and it is a curious fact to contemplate, that their eyes (fig. 12) should have been preserved perfect; theypresent one of those wonderful objects which carry one's thoughts backwards to the early ages of the world, probably many millions of years, and yet it is found by the peculiar structure of the eyes of these Trilobites that they were placed at the bottom of the sea with perfect power to look upwards at the light of the sun through the transparent waters. The same hand and the same power had then Divine care and solicitude for the well-being of His creatures, as great as He has for those of later ages, and these first-formed beings exactly correspond with the account of the creation of animals given in the book of Genesis, "And God said, let the waters bring forth abundantly the moving creature that hath life."

FIG. 12.—EYE OF TRILOBITE.

At the end of the "transition period"—after ages of long-continued disintegration of the rough surface of the earth, and its deposition in strata—after thousands of generations of crustaceans, molluscs, and zoophytes had lived and died, depositing their shells at the bottom of the seas, so as to form strata of the carbonate of lime—a great and terrific convulsion of nature put a stop to all this quiet and systematic order of things; for through these long reaches of time, the physical laws of nature had continued to exert their influence, the bulk of the world had gone on radiating its heat into space, and, as a necessary result, had gradually contracted in size. Now, this radiation had doubtless been much retarded by the badly-conducting surface of solid matter which had everywhere covered it, but, although retarded, it could not be prevented, and although the crustof solid matter may already have been several miles in thickness, yet this in relation to the bulk of the earth would hold but the proportion of the paper on the surface of a twelve-inch globe. As the fluid mass of the earth continued to contract, there would of course be a great stress or crushing-power exerted on the crust, both by its own gravity and that of the air which surrounded it, and about this period it appears to have given way over the greatest portion of the globe, producing enormous rents and fractures, seen in every country in the faults and dislocations of these primitive and transition strata, some of which were driven up by the downward force of others, and left in a perpendicular position, some overlapping each other, &c.; but the greatest effect of this convulsion appears to have been produced by the rocking or rolling surface of the sub-existing fluid world, forming gigantic waves, which, by meeting in opposite directions and thrusting upwards the strata to a great height, formed the mighty mountain-chains of the now-existing earth, which raise their lofty pinnacles above the clouds. Now, these mountains may at first thought appear too ponderous and extensive to be thrown up in this way; but by inspecting the engraved section of a part of the globe (fig. 13), it will be seen how very insignificant a mountain is when compared with the whole world. This section is through Asia from the Persian Gulf to the Yellow Sea, and embraces the highest land on the whole face of the earth, and is drawn on a scale in which the earth is represented by a globe sixteen inches diameter. The rugged and peaked tops of these mountains would be formed by the great fractured masses of the broken strata being thrust upwards and there resting against each other; but who can describe the chasms and hollows which must have resulted when the great wave of melted earth had subsided to its level under one of these huge mountain masses? or the dreadful abyss into which at some future time it and the surrounding country may fall, if they have not already been filled up by the sinking of the surrounding strata. Some of these great waves, when thrust upwards, forced their way right through the point of the mountain andcame pouring down in torrents of liquid earth (lava), deluging the surrounding country and filling up the beds of the adjacent seas, casting out cinders and ores of metals—as iron, which appears to have first made its appearance at that time, mingling with the deposits and tinging them of a red colour. These great volcanoes, upon the subsidence of the rock-waves, still (more or less) retained their communication with the interior fiery earth, and are now the greatest safeguards against such a general crushing-up of the strata, for they act as safety-valves against any unequal expansion of the interior (fig. 14). The greatest eruptions of volcanoes or the most terrific earthquakes of modern times, are as the most insignificanttrifles compared with what must have taken place to form the inequalities of surface found to exist.

FIG. 13—SECTION OF 40 DEG. OF THE EARTH'S SURFACE, BEING THE SOUTHERN PART OF ASIA, AND INCLUDING THE HIGHEST LAND IN THE WORLD.

The outer uneven line represents the mountains and table-lands from the sea's level, and the lower line shows the depth to which the crust of the earth's surface has been examined—about five miles.

A to B.—Level of sea.B to second C.—Hindustan.C to D.—Thibet.D to E.—Great Desert of Gobi.F.—500 miles of Earth's radius.C to C.—The Himalayas, in which occurs the highest mountain in the world, Dhawalagiri, which is 28,174 feet high.

FIG. 14.—BURNING MOUNTAIN.

But the contraction of the interior mass of the earth still continues, and the cavities left by the expulsion of volcanic matters, and the pushing-up of the mountains, may not all have been compensated for by the sinking-in of the strata, so it remains a matter of doubt whether the crust of the earth is sufficiently strong to bear the pressure of its own and the air's gravity, or whether at some future day another contraction will break it up and destroy the whole existing order of things. The shocks of earthquakes are strictly analogous to such catastrophes, but on an immensely inferior scale.

FIG. 15.—LIMESTONE MADE UP OF ENCRINITE.

FIG. 16.—LIMESTONE MADE UP OF CORALS (Favosites polymorpha).

The effects of the last great contraction having subsided the surface of the earth assumed a new arrangement of its matter, and the order of things which caused the deposition of the secondary strata commenced. Sedimentary sandstones were deposited from the washings of the surface by the waters which had not yet absorbed all the superfluouscarbonic acid of the air, but continued to do so, and as fast as it became absorbed and saturated with the calcareous matter of the soil, swarms of coral-polypi, which were then formed, began to build their habitations in the warm waters of the ocean and rob them of the carbonate of lime which they contained, leaving them capable of absorbing more fromthe atmosphere. These little creatures formed immense masses of coral, and together with the "Encrinites" (having stony frameworks, figs. 15 and 16), were the chief artificers of that age, and well did they show what perseverance was able to accomplish, for through the thousands of years of quiet which now succeeded, they must have filled up nearly all the existing oceans with their structures, causing the water gradually to flow from its former beds into other situations, and thus from time to time was changed the position of both sea and land. The strata of mountain limestone which now exist are the remains of what these little polypi then produced, for there is scarcely a portion of this kind of rock, but shows evidences of having been, once, coral, madrapore, or some analogous structure (fig. 17). This mountain limestone sometimes occurs thousands of feet thick, and extends over vast districts both in Europe and America.

FIG. 17.—ENCRINITIC LIMESTONE.

During this period, although there were no great disturbances, capable of displacing the strata, yet there appears to have been frequent small eruptions of volcanic matter through the crevices of the lower strata, filling up all their cracks and vacuities, and in many cases rising to the surface, overflowing with basalt, toadstone, and othervolcanic formations; in other cases rising in enormous quantities through openings at the bottom of the seas, partly filling these up, driving off the waters, and thus covering many of the coral formations with coatings of sand to a great thickness, raising up others into considerable elevations, and forming hills and fresh tracts of earth.

FIG. 18.—FOSSIL TREE FERNS.

During this long period of comparative quiet most of the irregularities on the surface of the earth became worn down, and extensive swamps were produced by partial evaporation of the inland lakes. These swamps were subject to occasional inroads of the sea, and at times formed shallow lakes or lagoons; in these grew the most luxuriant vegetation, gigantic pines, tree-ferns (fig. 18), equisetacæ, &c. These plants, nurtured by a hot and moist climate, acquired a great luxuriance of growth, and must have formed forests of suchgreat density, that there is nothing existing at the present time worthy to be compared with them, even in the hottest climates. Such fertility appears to have been dependent upon the conditions of the air and earth, the former containing more carbonic acid (the food of vegetables) and the latter a greater amount of warmth, than at present; these two circumstances, so favourable to the growth of plants, were equally unfavourable to the existence of air-breathing animals, to whom the carbonic acid would be fatal poison.

Thus, in the mighty hands of God, the air was undergoing a gradual purification, to fit it for the animals He intended to create; the polypi were extracting from the water all the carbonate of lime it was absorbing from the air and earth, and fixing it in the soil, to be of use in a hundred ways at some future time, while the vegetation growing in abundance extracted it from the air, and fixed its carbon in their leaves and substance generally; these vegetables, decaying and falling upon the surface of the earth, accumulated there for ages, and formed a carbonaceous matter which was afterwards changed by time and pressure into coal. The same thing (on a very much smaller scale) is taking place in the tropical forests of the present age; there the surface-soil is quite black, and consists of nothing but decayed leaves and wood for several feet in depth, but in the present time there are hosts of insects, every one of which feeds upon this vegetable matter, preventing to a great extent its accumulation, while in the former age there was nothing to destroy it when once deposited on the ground; so that the carbon of these forests of the secondary period, existing through perhaps tens of thousands of years, extracted from the air a sufficient quantity of vegetable carbonaceous matter to produce thick seams of coal, even when compressed by the superincumbent strata. These forests were subject from time to time to inroads of the sea produced by the before-mentioned causes, and thus it is found that the seams of coal are often buried by several hundred feet of sand, clay, shale, &c., above which the same growth recommenced to form a second strata of coal, and ages must have elapsed whilst each of the numerous seams which interstratify the"coal measures" were forming. This coal, preserved in the depths of the earth, now forms the greatest treasure of the mine, and ironstone (from which iron is procured) would be almost useless but for the occurrence of these two minerals together with limestone (used as a flux) in the same locality, and it is this fortunate circumstance which enables England to produce such vast quantities of iron at such a cheap rate. The quantity of coal consumed in the iron-smelting works and for fuel generally, is beyond what could have been imagined a generation or two back, being somewhere about 50,000,000 tons annually, the coal brought to London alone in 1856 being 1,271,800 tons, yet there is such a plentiful supply of this valuable fuel in Great Britain alone that, supposing the annual consumption to rise to 70,000,000, it would serve (according to computation) a thousand years. Who shall say from whence fuel will then be obtained? probably from some other source provided by the foreknowledge of God, as was shown in the formation of the coal itself; for who could have imagined, a thousand years ago, when England possessed such immense forests, and wood was the universal fuel, that this very wood would become too scarce and valuable to be used, and that a substitute would be dug out of the earth!

The coal-shales (thin layers of claystone found in the coal seams) furnish beautiful specimens of ferns and other plants turned into coal (fig. 19), or leaving their perfect impressions in the clay. The coal formation occurred during the latter part of one of those long eras of tranquillity which supervened upon the contraction and breaking-up of the older strata; but the laws of nature are immutable, and these days of comparative quiet again came to a close. The same phenomena before described again occurred, and there is hardly a square mile of these strata but shows evidences of the terrible convulsion which desolated the earth. Some of the strata were raised, others depressed, and some lost altogether, the cracks and flaws being filled with liquid lava or basalt, which in many cases rose upwards through them and overflowed the surface. Many of the cracks of this, the "carboniferous system," are filled with sulphuret of leadcalled "galena," the ore from which all the lead of commerce is obtained; it is not well known how the veins of this and similar substances got into these crevices, but it is probable they were injected in a fluid state by some unequal pressure on the liquid beneath, or deposited by electrical action.

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