rences of the existing epoch. We can judge from its thickness, and the nature of its rocks and fossils, that one system took much longer time to accumulate than another, but we cannot venture, by any known method of computation, to say how long in years. All that we have to do with is relative time; and even in dealing with the current epoch, should we assert that certain events took place more than six thousand or eight thousand years ago, we are simply asserting a provisional opinion, and not maintaining a belief like that founded upon the written record of human history.

The geological record is thus relative and not absolute; and when we arrange it, as in the subjoined tabulation, into Primary, Secondary, Tertiary, and Quaternary, we are merely asserting a certain order of succession, and this succession not always clearly defined over certain areas. Indeed it is often impossible to define the boundaries of the minor stages, portions having been removed by denudation, others overlaid by more recent deposits, and some being partially submerged beneath the waters of the ocean. Again, though the thickness of one formation may seem to have required a longer time for its accumulation than another of smaller dimensions, yet in the one case the rate of deposition may have been much more rapid than in the other, and the thinner may, after all, have required the longer period. Still further, though organic remains are most important aids, yet they are often absent from certain beds, or if there, these beds are not sufficiently exposed to investigation, and our information becomes in this way fragmentary and defective. Neither in sequence of events, nor in expression of time, does Geology lay claim to exactitude. Its cultivators are successfully labouring to complete the one, and they are hopeful of arriving at more definite terms in the other; but this is all in the mean time, and the fol

In this arrangement the terms Eozoic, Palæozoic, Mesozoic, and Cainozoic, indicate the chronological stages having reference to the ascent of life; and Laurentian, Cambrian, Silurian, &c., those having reference to the different formations whose depositions mark the successive physical operations of nature. By this arrangement the geologist simply asserts that the Laurentian preceded the Cambrian, and the Cambrian the Silurian; but no opinion is expressed as to the amount of time required for the deposition of the Laurentian, or whether the Cambrian occupied a longer time in formation than the overlying Silurian. We may feel convinced, from the total thickness of a system, the alternations of its strata, and the succession of its fossils, that it occupied a much longer time in formation than another system; but this is not expressed in the above arrangement, which merely affirms a sequence from older to younger, and from the earliest ascertainable operations to those still taking place around us.

Such is the chronology of Geology-a chronology to which investigators endeavour to conform the rock-formations of the globe; and although the chalk of one country, for example, may not have been exactly contemporaneous with

the Chalk formation of another region, still we know that it stands intermediate between the Oolite and Tertiary, and can therefore assign to it a place relatively to these formations. In some region yet unexplored a whole suite of strata may be discovered older than our Carboniferous, and yet younger than our Old Red, and in such a case geologists would give the new formation a name, and place it as intermediate between these two systems. It would disturb no established order, but merely render more complete the sequence, like the interpolation of a hitherto unknown reign in the dynasties of human history. The geological record is thus a thing of mere sequence—an inconceivable amount of unexpressed time, during which certain events follow each other in definite order. How many ages have elapsed since the first deposition of the Laurentian strata we cannot tell; how many centuries were spent in the formation of the Coal-measures of any locality, we can only, estimating from existing operations, offer the widest conjecture. But we can affirm with certainty, and this is a great point gained, that one rock-system is younger than another; that these rock-systems follow in the order above given; that according to our present knowledge invertebrate life preceded the vertebrate; that fishes preceded reptiles, reptiles birds, and birds mammalia.* We can also affirm, what it is the object of the present Sketch to prove, that as there has been an ascent in time from lower to higher forms of life, so Man, being the highest known creature, comes latest on the geological stage, and that evidences of his existence are to be found only in the most recent and superficial formations.

It will be seen from the preceding statements that the geological record is avowedly indefinite and defective-indefinite, as it deals only with relative time; and defective, as many strata cannot be assigned to their proper positions, * See tabulation of ascending orders, p. xv, 29.

partly from the obscurities of superposition, and partly from the absence of typical fossils to connect them. But, while admitting this defect in details, it must not be imagined there is any uncertainty as to the broader features of the record, or that any new discoveries have ever been at variance with the great order of sequence which modern geology has established. Man, so far as every known fact tends to indicate, belongs exclusively to the Recent or Post-tertiary period. No remains of his kind, no fragment of his works, no traces of his presence, have ever been detected in earlier formations. But though this is admitted on all hands, the question still remains, at what stage of the Post-tertiary are traces of his existence first detected? Till recently the general belief has been that man's first appearance on the globe dates back, at the very most, to little more than six or seven thousand years; and so incorporated had this belief become with others of a more sacred character, that few, even though doubting, had the boldness to express a contrary conviction. Like the age of our planet, which was also at one time restricted to a few thousand years, the antiquity of man has become a question of science and reason; and well-informed minds are now prepared to admit that as the earth has existed for untold ages, so man, its latest creation, may have inhabited its surface for hundreds of centuries. The evidence is purely geological, and as such ought to be treated like any other problem in science, without bar or hindrance from preconceived opinion; or, as it has been well said by Bishop Tait, in his address to the Philosophical Institution of Edinburgh, "The man of science ought to go on honestly, patiently, diffidently, observing and storing up his observations, and carrying his reasonings unflinchingly to their legitimate conclusions, convinced that it would be treason at once to the dignity of science and of religion, if he sought to help either by

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swerving ever so little from the straight rule of truth." In investigating the antiquity of man we are dealing with a question of natural history, and are bound by the same methods of research as if we were treating of the history of the mammoth or mastodon. Our business as geologists is to examine the rock-formations composing the earth's crust, to note their embedded organisms, and to fix their relative antiquities. Wherever the remains of man or of his works occur, there, we presume, has been his presence; and though we cannot assign any definite date to the time of such occurrence, we are at all events entitled, judging from all the correlative circumstances, to say that it took place more than six thousand, ten thousand, or twenty thousand years ago. In other words, we are bound to deal with Man's antiquity as with any other question in geology; and though our dates be merely relative, we can affirm the order of sequence, and arrive at some notion of duration from the rate of existing operations.

Abiding by these methods, we find the remains of man and of his works gradually receding from the historical into the pre-historic ages. In Southern and Western Europethe only regions that have been examined with anything like geological accuracy-these remains occur in peat-mosses, in lake-silts, river-drifts, and cave-earths, and from their associated organisms we judge of their relative antiquities. If they occur along with the remains of the existing horse, ox, sheep, pig, and the like, we know that they are comparatively recent, and in all probability belong to the historic era. If, on the other hand, they are found accompanied by remains of extinct species of horses and oxen, we know they are of greater antiquity; and if such horses and oxen are not spoken of in history, or represented in human monuments, then we are entitled to regard them as pre-historic. Or again, if they are associated with remains of the great