Such being the manner of the formation of the crust of the world, can we form any judgment of its duration and durability? If we could measure the rate of the attrition of the present continents, we might estimate the duration of the older continents whose attrition supplied the material for the present dry land. But as we cannot measure the wearing-away of the land, we can merely state generally, first, that the present dry land required an indefinitely long period for its formation; second, that the previous dry land which supplied material for its formation required equal time to make; third, that there is at present land forming at the bottom of the sea which in time will appear above the surface; fourth, that we find no vestige of a beginning, or of an end.
Granite has in its own nature no claim to originality, for it is found to vary greatly in its composition. But, further, it is certain that granite, or a species of the same kind of stone, is found stratified. It is the _granit feuilletee_ of M. de Sauffure, and, if I mistake not, is called _gneiss_ by the Germans. Granite being thus found stratified, the ma.s.ses of this stone cannot be allowed to any right of priority over the schistus, its companion in Alpine countries.
Lack of stratification, then, cannot be considered a proof of primitive rock. Nor can lack of organized bodies, such as sh.e.l.ls, in these rocks, be considered a proof; for the traces of organized bodies may be obliterated by the many subsequent operations of the mineral region. In any case, signs of organized bodies are sometimes found in "primitive"
mountains.
Nor can metallic veins, found plentifully in "primitive" mountains, prove anything, for mineral veins are found in various strata.
We maintain that _all_ the land was produced from fused substances elevated from the bottom of the sea. But we do not hold that all parts of the earth have undergone exactly similar and simultaneous vicissitudes; and in respect to the changes which various parts of the land have undergone we may distinguish between primary and secondary strata. Nothing is more certain than that there have been several repeated operations of the mineralising power exerted upon the strata in particular places, and all those mineral operations tend to consolidation. It is quite possible that "primitive" ma.s.ses which differ from the ordinary strata of the globe have been twice subjected to mineral operations, having been first consolidated and raised as land, and then submerged in order to be again fused and elevated.
_II.--The Nature of Mineral Coal_
Mineral, or fossil, coal is a species of stratum distinguished by its inflammable and combustible nature. We find that it differs in respect to its purity, and also in respect to its inflammability. As is well known, some coals have almost no earthy ash, some a great deal; and, again, some coals burn with much smoke and fire, while others burn like c.o.ke. Where, then, did coal come from, and how can we account for its different species?
A substance proper for the formation of coaly matter is found in vegetable bodies. But how did it become mixed with earthy matter?
Vegetable bodies may be resolved into bituminous or coaly matter either by means of fire or by means of water. Both may be used by nature in the formation of coal.
By the force of subterranean heat vegetable matter may have been charred at the bottom of the sea, and the oleaginous, bituminous, and fuliginous substances diffused through the sea as a result of the burning may have been deposited at the bottom of the sea as coal. Further, the bituminous matter from the smoke of vegetable substances burned on land would ultimately be deposited from the atmosphere and settle at the bottom of the sea.
Many of the rivers contain in solution an immense quant.i.ty of inflammable vegetable substance, and this is carried into the sea, and precipitated there.
From these two sources, then, the sea gets bituminous material, and this material, condensed and consolidated by compression and by heat, at the bottom of the sea, would form a black body of a most uniform structure, breaking with a polished surface, and burning with more or less smoke or flame in proportion as it be distilled less or more by subterranean heat. And such a body exactly represents our purest fossil coal, which gives the most heat and leaves the least ash.
In some cases the bituminous material in suspension in the sea would be mixed more or less with argillaceous, calcareous, and other earthy substances; and these being precipitated along with the bituminous matter would form layers of impure coal with a considerable amount of ash.
But there is still a third source of coal. Vegetable bodies macerated in water, and consolidated by compression, form a body almost indistinguishable from some species of coal, as is seen in peat compressed under a great load of earth; and there can be no doubt that coal sometimes originates in this way, for much fossil coal shows abundance of vegetable bodies in its composition.
There remains only to consider the change in the disposition of coal strata. Coal strata, which had been originally in a horizontal position, are now found sometimes standing erect, even perpendicular. This, also, is consistent with our theory of the earth. Indeed, there is not a substance in the mineral kingdom in which the action of subterranean heat is better shown. These strata are evidently a deposit of inflammable substances which all come originally from vegetable bodies.
In this stage of their formation they must all contain volatile oleaginous const.i.tuents. But some coal strata contain no volatile const.i.tuents, and the disappearance of the volatile oleaginous substances must have been produced by distillation, proceeding perhaps under the restraining force of immense compression.
We cannot doubt that such distillation does take place in the mineral regions, when we consider that in most places of the earth we find the evident effects of such distillation in the naphtha and petroleum that are constantly emitted along with water in certain springs. We have, therefore, sufficient proof of this operation of distillation.
_III.--The Disintegration and Dissolution of Land_
Whether we examine the mountain or the plain, whether we consider the disintegration of the rocks or the softer strata of the earth, whether we regard the sh.o.r.es of seas or the central plains of continents, whether we contemplate fertile lands or deserts, we find evidence of a general dissolution and decay of the solid surface of the globe. Every great river and deep valley gives evidence of the attrition of the land.
The purpose of the dry land is to sustain a system of plants and animals; and for this purpose a soil is required, and to make a soil the solid strata must be crumbled down. The earth is nothing more than an indefinite number of soils and situations suitable for various animals and plants, and it must consist of both solid rock and tender earth, of both moist and dry districts; for all these are requisite for the world we inhabit.
But not only is the solid rock crumbling into soil by the action of air and water, but the soil gradually progresses towards the sea, and sooner or later the sea must swallow up the land. Vegetation and ma.s.ses of solid rock r.e.t.a.r.d the seaward flow of the soil; but they merely r.e.t.a.r.d, they cannot wholly prevent. In proportion as the mountains are diminished, the haugh, or plain, between them grows more wide, and also on a lower level; but while there is a river running on a plain, and floods produced in the seasons of rain, there is nothing stable in the const.i.tution of the surface of the land.
The theory of the earth which I propound is founded upon the great catastrophes that can happen to the earth. It supposes strata raised from the bottom of the sea and elevated into mountainous continents.
But, between the catastrophes, it requires nothing further than the ordinary everyday effects of air and water. Every shower of rain, every stream, partic.i.p.ates in the dissolution of the land, and helps to transport to the sea the material for future continents.
The prodigious waste of the land we see in places has seemed to some to require some other explanation; but I maintain that the natural operations of air and water would suffice in time to produce the effects observed. It is true that the wastage would be slow; but slow destruction of rock with gradual formation of soil is just what is required in the economy of nature. A world sustaining plants and animals requires continents which endure for more than a day.
If this continent of land, first collected in the sea, is to remain a habitable earth, and to resist the moving waters of the globe, certain degrees of solidity or consolidation must be given to that collection of loose materials; and certain degrees of hardness must be given to bodies which are soft and incoherent, and consequently so extremely perishable in the situation in which they are now placed.
But, at the same time that this earth must have solidity and hardness to resist the sudden changes which its moving fluids would occasion, it must be made subject to decay and waste upon the surface exposed to the atmosphere; for such an earth as were made incapable of change, or not subject to decay, would not afford that fertile soil which is required in the system of this world--a soil on which depends the growth of plants and life of animals--the end of its intention.
Now, we find this earth endued precisely with such degree of hardness and consolidation as qualifies it at the same time to be a fruitful earth, and to maintain its station with all the permanency compatible with the nature of things, which are not formed to remain unchangeable.
Thus we have a view of the most perfect wisdom in the contrivance of that const.i.tution by which the earth is made to answer, in the best manner possible, the purpose of its intention, that is, to maintain and perpetuate a system of vegetation, or the various races of useful plants, or a system of living animals, which are in their turn subservient to a system still infinitely more important--I mean a system of intellect. Without fertility in the earth, many races of plants and animals would soon perish, or be extinct; and with permanency in our land it were impossible for the various tribes of plants and animals to be dispersed over the surface of a changing earth. The fact is that fertility, adequate to the various ends in view, is found in all the quarters of the world, or in every country of the earth; and the permanency of our land is such as to make it appear unalterable to mankind in general and even to impose upon men of science, who have endeavoured to persuade us that this earth is not to change.
Nothing but supreme power and wisdom could have reconciled those two opposite ends of intention, so as both to be equally pursued in the system of nature, and so equally attained as to be imperceptible to common observation, and at the same time a proper object of the human understanding.
LAMARCK
Zoological Philosophy
Jean Baptiste de Monet, Chevalier de Lamarck, was born in Picardy, France, Aug. I, 1744, the cadet of an ancient but impoverished house. It was his father"s desire that he should enter the Church, but his inclination was for a military life; and having, at the age of seventeen, joined the French army under De Broglie, he had within twenty-four hours the good fortune so to distinguish himself as to win his commission. When the Museum of Natural History was brought into existence in 1794 he was sufficiently well-known as a naturalist to be entrusted with the care of the collections of invertebrates, comprising insects, molluscs, polyps, and worms.
Here he continued to lecture until his death in 1829. Haeckel, cla.s.sifying him in the front rank with Goethe and Darwin, attributes to him "the imperishable glory of having been the first to raise the theory of descent to the rank of an independent scientific theory." The form of his theory was announced in 1801, but was not given in detail to the world until 1809, by the publication of his "Zoological Philosophy" ("Philosophie Zoologique"). The Lamarckian theory of the hereditary transmission of characters acquired by use, disuse, etc., has still a following, though it is controverted by the schools of Darwin and Weissmann.
Lamarck died on December 18, 1829.
_I.--The Ladder of Life_
If we look backwards down the ladder of animal forms we find a progressive degradation in the organisation of the creatures comprised; the organisation of their bodies becomes simpler, the number of their faculties less. This well-recognised fact throws a light upon the order in which nature has produced the animals; but it leaves unexplained the fact that this gradation, though sustained, is irregular. The reason will become clear if we consider the effects produced by the infinite diversity of conditions in different parts of the globe upon the general form, the limbs, and the very organisation of the animals in question.
It will, in fact, be evident that the state in which we find all animals is the product, on the one hand, of the growing composition of the organisation which tends to form a regular gradation; and that, for the rest, it results from a mult.i.tude of circ.u.mstances which tend continually to destroy the regularity of the gradation in the increasingly composite nature of the organism.
Not that circ.u.mstances can effect any modification directly. But changed circ.u.mstances produce changed wants, changed wants changed actions. If the new wants become constant the animals acquire new habits, which are no less constant than the wants which gave rise to them. And such new habits will necessitate the use of one member rather than another, or even the cessation of the use of a member which has lost its utility.
We will look at some familiar examples of either case. Among vegetables, which have no actions, and therefore no habits properly so called, great differences in the development of the parts do none the less arise as a consequence of changed circ.u.mstances; and these differences cause the development of certain of them, while they attenuate others and cause them to disappear. But all this is caused by changes in the nutrition of the plant, in its absorptions and transpirations, in the quant.i.ty of heat and light, of air and moisture, which it habitually receives; and, lastly, by the superiority which certain of its vital movements may a.s.sert over the others. There may arise between individuals of the same species, of which some are placed in favourable, others amid unfavourable, conditions, a difference which by degrees becomes very notable.
Suppose that circ.u.mstances keep certain individuals in an ill-nourished or languid state. Their internal organisation will at length be modified, and these individuals will engender offspring which will perpetuate the modifications thus acquired, and thus will in the end give place to a race quite distinct from that of which the individual members come together always under circ.u.mstances favourable to their development.
For instance, if a seed of some meadow flower is carried to dry and stony ground, where it is exposed to the winds and there germinates, the consequence will be that the plant and its immediate offspring, being always ill-nourished, will give rise to a race really different from that which lives in the field; yet this, none the less, will be its progenitor. The individuals of this race will be dwarfed; and their organs, some being increased at the expense of the rest, will show distinctive proportions. What nature does in a long time we do every day ourselves. Every botanist knows that the vegetables transplanted to our gardens out of their native soil undergo such changes as render them at last unrecognisable.
Consider, again, the varieties among our domestic fowls and pigeons, all of them brought into existence by being raised in diverse circ.u.mstances and different countries, and such as might be sought in vain in a state of nature. It is matter of common knowledge that if we raise a bird in a cage, and keep it there for five or six years, it will be unable to fly if restored to liberty. There has, indeed, been no change as yet in the form of its members; but if for a long series of generations individuals of the same race had been kept caged for a considerable time, there is no room for doubt that the very form of their limbs would little by little have undergone notable alteration. Much more would this be the case if their captivity had been accompanied by a marked change of climate, and if these individuals had by degrees accustomed themselves to other sorts of food and to other measures for acquiring it. Such circ.u.mstances, taken constantly together, would have formed insensibly a new and clearly denned race.
The following example shows, in regard to plants, how the change of some important circ.u.mstance may tend to change the various parts of these living bodies.
So long as the _ranunculus aquatilis_, the water b.u.t.tercup, is under water its leaves are all finely indented, and the divisions are furnished with capillaries; but as soon as the stalk of the plant reaches the surface the leaves, which develop in the air, are broadened out, rounded, and simply lobed. If the plant manages to spring up in a soil that is merely moist, and not covered with water, the stems will be short, and none of the leaves will show these indentations and capillaries. You have then the _ranunculus hederaceus_, which botanists regard as a distinct species.
Among animals changes take place more slowly, and it is therefore more difficult to determine their cause. The strongest influence, no doubt, is that of environment. Places far apart are different, and--which is too commonly ignored--a given place changes its climate and quality with time, though so slowly in respect of human life that we attribute to it perfect stability. Hence it arises that we have not only extreme changes, but also shadowy ones between the extremes.
Everywhere the order of things changes so gradually that man cannot observe the change directly, and the animal tribes in every place preserve their habits for a long time; whence arises the apparent constancy of what we call species--a constancy which has given birth in us to the idea that these races are as old as nature.
But the surface of the habitable globe varies in nature, situation, and climate, in every variety of degrees. The naturalist will perceive that just in proportion as the environment is notably changed will the species change their characters.
It must always be recognised:
(1) That every considerable and constant change in the environment of a race of animals works a real change in their wants.