It has also been so far anticipated in the earlier part of this essay, that we only need here repeat that they are not found in the lower primary strata, from gneiss up to the latest argillaceous schists, except, in one instance, in quartz rock. In the same part of this article, it was shown not to be impossible that they should occur in some, and beneath many, of these ; and that geologists were not yet entitled, from their limited acquaintance with this part of the subject, to pronounce a negative as to any rocks, except, perhaps, the gneiss of granitic aspect which is connected with granite.
With respect to the secondary strata, it was also shown that they do not occur in the lowest, or the sandstone, but commence in the subsequent, or first limestone ; that, in the coal strata, vegetable remains abounded, that marine bodies then appeared again in the red marl, and continued even up to the chalk, where the general marine strata may be supposed to cease, and that, after this, in certain situations, irregular alternations of marine and fresh-wa ter beds occurred, in which numerous fossil remains of various kinds were abundant The probable causes of these irregularities were also examined at the same time, and reasons were assigned, arising out of the habits of the animals themselves, the various rapidity with which the earthy matters may have been deposited under the sea, and the other numerous accidents which might. have destroyed their colonies, or subverted the rocks in which they had been deposited.
Physiologists, under the influence of poetical feelings, or reasoning on metaphysical principles, have speculated much on the creation of animated beings, while others, deficient in information on these subjects, have pursued an ignis fatuus of their own creation, beyond the regions of experience, of philosophy, or even of common sense. Those who may delight in such speculations, in inquiries re specting organic molecules, on the original imperfection and gradual improvement of animal species, on the pos sibility of converting one species into another, and on the ultimate perfectibility of the living creation, must be referred to those authors in whom they will certainly find amusement, if not instruction ; to Buffon, and Darwin, and Condorcet, and Godwin, and many more. On these subjects we can learn nothing from the usual sober and plodding paths of investigation and experience.
Inquirers of a character somewhat more cautious have, however, conceived, that the earlier species of animals are less perfect than the more recent; and thus, by gene ralizing on this principle a little more, they have imagined that they could trace a gradual improvement in the nature and organization of created animals. This is a question, however, that ought- to be examined by actual investigation. It lies in the department of organic geology, if any where, and may be examined, however imperfectly at present, by the evidence which this branch of the science furnishes.
There is another collateral inquiry connected with this, which relates to the numerical increase of species. There is not a great deal to be offered on either of these ques tions; but such as the evidence is on this and such colla teral subjects as may branch from it, we must here at tempt to give a brief sketch of the facts. To enter into minute zoological and botanical details is not possible within the prescribed limits.
It must be already apparent, that any theory on these subjects necessarily labours under radical imperfections in regard to evidence. If, following the order of the strata upwards, we can actually determine a certain suc cession of species, we have no certainty respecting its truth, and less respecting its perfection. From the pre ceding observations on the positions of organic fossils as they regard the different strata, it seems abundantly evident, that the series known to us is very imperfect, particularly in its more remote parts. We know not what has been destroyed ; nor do we know when or where that has hap pellet], so as to be liable to pronounce on a position, from evidence which is merely negative.
We may imagine, if we please, as many have done, that the early inhabitants of the globe were purely marine ; we may even suppose that they were limited to lithophy tes or to shell fish. But the facts, if taken with all the collateral circumstances, are far from proving even this. All the stratified rocks in question have been formed un der the water of the sea, and hence it is a necessary con sequence, that all the organic substances which they con tain should be marine. Many marine animals are of a perishable nature, and could not have withstood the va rious changes and accidents under which they ought to have been preserved ; and hence organic fossils, and those, in particular, which must have been in circumstances to have suffered most, are limited to such as were of the most durable nature. It is not sufficient to draw this evidence front the actual presence of these bodies alone, without adverting to all the circumstances under which they lived, died, were fixed in the solid state, and subse quently exposed to great changes, and to extensive and violent revolutions. That the softer fishes, containing few bones, and those neither large nor durable, should have utterly disappeared, while shells and corals have been preserved, is an effect that might have been anticipated. It is almost proved, by finding these animals rarely in cer tain strata where shells abound, or by finding in some places their harder parts alone. Hence, for aught we can prove to the contrary, the most early ocean, of which these records alone exist, deficient and imperfect, though pre served in stone, might have teemed with as great variety of animal life as the present.