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NOTE III. p. 39.

THEORIES OF IGNEOUS ROCKS.

All those speculations regarding the primary condition of matter, and the original formation of the sphere of the earth, are of a very unprofitable nature, in so far as the phenomena attending them cannot be compared to any operations at present in action. It is evident that we now see matter only as it has undergone various chemical combinations and changes, and under forms and obeying laws totally different from its original condition. The oblate spheroidal figure of the earth has been thought to imply a state of fluidity of the whole mass: yet there are no valid grounds for assuming this; for the matter of the globe may just as readily be supposed to have been formed into this particular figure, to suit subsequent laws of rotatory motion, before even the law of fluidity was imposed upon it. Neither are we at all certain whether the globe be a solid sphere of matter with a density increasing towards the centre, or a hollow ball. The experiments of Maskelyne and Playfair, if accurate, would rather indicate the former condition, proving its mean density to be five times that of water. On the other hand, the existence of a highly elastic medium occupying the centre, is not an improbable supposition, and perhaps more in accordance with the economic analogies of nature; for in none other of her works do we witness that prodigal waste (if the term may be allowed) which such an enormous mass of matter, apparently for no immediate use, would indicate. The well known luminous theory of the late Sir John Leslie may thus turn out, after all, a most brilliant idea.

The existence of the different earths which compose the principal mass of the crust of the globe in a metallic state, as shewn by the splendid discoveries of Davy, and

the farther application of these to the origin of volcanic phenomena, as prosecuted by that distinguished philosopher, and by Dr Daubeny, are theories now very generally adopted by geologists. These theories certainly account for the production of all the varieties of igneous rocks in a much more satisfactory way than any other; yet we must by no means conclude, that the discovery of the metallic basis of the earths has brought us to the ultimate elements of things. We know so little of matter, that it may be perfectly possible that it consists of only one simple element, or, to take the Platonic doctrine, two, and that all its varied aspects may be due to the various laws imposed upon it.

If we view the elevation of igneous rocks, then, as portions protruded from the matter of the earth's crust by chemical actions, the magnitude of these, compared. to the mass of the earth's diameter, dwindles into mere insignificance, and need not demand any lengthened eras for their production. See Section, Plate IV.

NOTE IV.

p. 42.

SUCCESSIVE CREATIONS OF ANIMALS.

"When I endeavour to prove that the rocky strata contain the skeletons of several genera, and the loose strata those of several species, all of which have ceased to be existing animals, I do not pretend that a new creation was required for calling our present races of animals into existence. I only urge that they did not anciently occupy the same places, and that they must have come from some other part of the globe."*

It is somewhat extraordinary that those theorists who profess to draw their deductions exclusively from causes now in operation, should yet so unceremoniously

*

Cuvier, Recherches sur les Ossmens Fossiles, tom. i. 1821.

advance the proposition of a successive production of new species, when there is evidently no such law or fact to be found in nature. The idea of spontaneous production has long ago been scouted from science, and the no less illogical one of equivocal generation is fast going. We see no analogy in nature to lead us to suppose that such a law exists

we see no

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provision for such operations, and no trace of such having ever occurred we can predicate that the earth will produce certain plants after we have deposited certain seeds, but that if such seeds are carefully excluded, that no species of vegetation will followcan predicate that a lupin seed will produce a certain flower, followed by a seed similar to the parent one; and we may speculate freely on certain varieties of these, which circumstances may modify the production of, but we know to a certainty, from experience and analogy, that the lupin can never produce a rose, and that the soil alone will never bring forth a new species of plant.

It is fair to presume, then, that as the origination of species is unknown in nature, it does not exist. It is asserted that it does exist, but that the periods of its operation are at immensely distant intervals. This is a mere assertion, without proof by facts, and is contradicted by analogy; for the periods of germination and animal reproduction are all within limited cycles, depending on circumstances, which occur periodically, and which are apparent as contrivances in nature. The "recent introduction of man on the globe" has been given as an example of repeated acts of creation. But this is merely assuming as a fact a conjecture, of which we have no conclusive proof.

A reasoner of another school may say, that as organized beings were created at first, new species may be afterwards added by a special repeated act of the Creator. It may be answered, that we are told that organized beings were at first made by the Creator, but

we have no information of subsequent operations of a similar kind; and having no good grounds to prove it, the assumption of such after acts is illogical. For, suppose we were to assume the reverse proposition, - that the creation of organic beings was an act that was accomplished at once, under peculiar eircumstances, and which it was impossible to repeat, this is just as tenable and irrefragable an argument as the other. It is astonishing on what flimsy grounds even such a mind as that of Blumenbach could speculate on this subject. Because the animalcule, called the vibrio aceti, is found only in stale vinegar, a substance produced by civilized man, this philosopher argues, that this being must have been of recent creation or origin. Yet a moment's reflection might have convinced this acute naturalist, that similar products to vinegar exist in nature, and must have existed from the beginning-as in sour grapes, a decaying sugar-cane, and every other vegetable with fermenting saccharine juices. We have entered more at large into this subject in a paper in the Edinburgh Journal of Natural and Geographical Science, vol. II. 1830.*

Linnæus conjectured that plants and animals originally radiated from a common centre in the tropical zone of the primitive earth, where the altitude of mountains produced that variety of climate suited to their different natures, and that thus a gradual diffusion took place over the whole earth.

A modification of some theory of this kind might be employed to explain the appearances of our fossiliferous strata, in opposition to that of successive creations, and may be thus exhibited in the following diagram :

* We beg to state, that both here and in the text, we do not attempt to prove that successive creations of organized beings may not have taken place, but that hitherto we have no direct proofs of such.

[graphic][merged small][merged small][merged small][merged small][merged small][merged small]

d1, d2, d 3, d 4, Detrital matter formed in ancient seas, with animals and vegetables emanating from primary centre.

e, New continents subsequently elevated, forming the present land.

The successive circles, d, d, d, d, may indicate the several formations; d 4 being the first deposit in the depths of the ocean, and containing the remains of animals that formed the pioneers of the yet untenanted spaces around; d 3, d 2, d 1, representing the next orders in succession. To fill up this hypothetical sketch, we must suppose other centres formed contemporaneously, but under different modifications; and that repeated elevations of the marine strata took place, by which the ocean level, and other circumstances, were so altered as to interrupt the farther increase of the same species in the same localities, while at the period or periods when this ocean bed finally became dry land, the temperature was so changed as to admit of a more complete separation of genera and species, and their more varied dispersion over the globe.

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