to time, we have ocular proof of their extent in space. All that geology establishes, then, in this particular, is the fact of the gradual origination of new species, but by no means the particular method or process by which it has been brought about.

It is true there have not been wanting theories to explain these processes on natural principles. Yet of these, the most celebrated have failed to stand the test of increasing observation; while none, perhaps, have been altogether satisfactory or free from material objections. Physical research cannot bring us to any distinct idea of the nature of creation. If we consider the simple case of the introduction of a single new species, or even individual of a new species, there is an obvious limit imposed on our speculations. On the other hand, it is freely open to the physical inquirer to trace, as closely as possible, the secondary means, as far as the nature of the case admits; to investigate rigorously, for example, all the modifications which change of climate, domestication, crossing of breeds, &c., may produce. Such inquiries may be far from successful; they may lead only to some few imperfect conclusions utterly insufficient to ground any theory upon; but certainly this is the only course open to the inductive inquirer.

The question respecting the immutability of species, and the possibility of a transition from one into another; of such modifications as we observe in intermediate races being perpetuated; of new species being thus eventually introduced; with the

various collateral topics which are involved in these inquiries, have all formed the subjects of anxious debate, and even of animated controversy, among physiologists. There has undoubtedly been a preponderance of evidence against the notion; and the high authority of Cuvier has been claimed as heading the phalanx of the opponents. Whilst on the other hand, Geoffroy St. Hilaire has spoken of the "age of Cuvier" as approaching its termination, and the immutability of species as a conviction fast fading away from men's minds. All that I presume to observe on such a subject is this: that it is a question fairly open to philosophical discussion; and one which is at any rate the only avenue to a scientific solution of the problem. If natural science be ever able to conduct us to the knowledge of such a point, it must be by some such route as this. And we have no more reason to despair of its doing so in this case than in any of the other instances of philosophical discovery, which in a past age might have been pronounced as hopeless and visionary as some are now disposed to consider this. While we must also recollect that all the conclusions which have been deduced from the observed facts relating to the modifications of species are restricted by the condition of the short period of time during which their operation has been contemplated; and that we must admit as essentially influential the very different circumstances which might affect similar operations continued through unlimited periods of past duration.

The appeal to another kind of evidence, to knowledge derived from another source than that of physical inquiry conducted on the principles of established natural analogies, would merely transfer our inquiry out of the pale of physical science into that of moral authority, and would consequently divest it of all force in respect to the purpose of substantiating the great truths of natural theology. The proper conclusions of physical inquiry are to be directed only to the two simple points, the actual occurrence of successive originations of species, and the elucidation, as far as possible, of the secondary means by which those originations may have been brought about.

Geology, then, affords abundant proof of the fact that there was a time when the present races of organized beings did not exist, and consequently bears direct testimony to the occurrence of what we term creation; that is, the introduction of new species; as it does also of the previous introduction of a vast series of other species, of which it also shows the successive extinction. But the evidence is perfectly clear as to the gradual character of this introduction of species. Those now existing are found to have co-existed with others now extinct, as these did in their turn with those of older date, until we arrive at periods when whole genera and classes were entirely different. But at no period do we find an absence of organized life followed by a simultaneous universal production of it.

When, therefore, on geological grounds, we speak of the evidence of creation, we must carefully bear in mind what is meant, and must restrict our meaning to the gradual appearance of one increasing family, while another was as gradually wasting away and disappearing. Geology, in a word, bears witness to a continued, perhaps perpetual successions of creations. It consequently tends infinitely to exalt our ideas of that eternal and overruling Omnipotence by whose agency they were brought about.

But no researches have disclosed the mode in which this has taken place, nor the process by which such a result of creative Omnipotence has been accomplished. It only assures us that it was not applied to all existing species at any one time. While, therefore, geology has been unable to trace the mode of the Divine operations, it has, beyond all question, substantiated the fact of such creative processes. And the leading truth of this gradual progress of the development of the varieties of organized life corresponding with changes in the disposition of the solid materials of the earth's surface, and of the temperature and climate, is perhaps among the most striking and beautiful points of evidence which geology affords to the conclusions of natural theology*.

Few truths are more impressive and sublime than

* For a full illustration of this point it is almost superfluous to refer the reader to Dr. Buckland's Bridgewater Treatise.

this unbroken continuance of uniform laws and harmonious adaptation to which geology bears testimony, existing throughout all the vast series of the successive orders of organized beings which have tenanted the globe, which, while it exhibits the greatest diversity in the forms of life and structure which have prevailed at different remote epochs, yet shows every where the preservation of the same most perfect harmony and analogy through periods of incalculable duration. And it is to be particularly observed how essential to this argument is the fact (before dwelt upon,) that all this was absolutely uninterrupted by any period of anarchy, by the occurrence of any general ruin or disorganization, by the intervention of any epoch at which the traces of organization were obliterated, or defaced, or disturbed, or at which, at least, a large part of the earth's surface was not teeming with animation, and richly furnished with all the accessories of life and enjoyment.

Remarks similar to those just made on the idea of creation, will in fact apply with considerable force to the entire argument of natural theology. Natural science can exhibit to us nothing but a series of physical causation; from this we infer design, that is, moral causation. But no such deduction can ever guide us to the discovery of the mode of operation, or enable us to trace the method by which the supreme volition executed its designs, or to supply the connecting link between physical and moral

causation.