tems," and "groups," and "series" each system being but the sediments of the lakes and seas of a certain period,. and characterised, of course, by its own peculiar fossils, as evidence of the life that prevailed during the time of its formation. And the reason is obvious: as land and sea have often changed places-the former at one time more insular, at another more continental; now sitting low and moist in the water, now elevated into lofty and arid regions; subjected at each change to diversity of colder or warmer ocean-currents, to new sets of winds, rains, and other climatal conditions-each period must necessarily have stamped its own impress on vegetable and animal life; and so it happens that the great rock-formations (the only records of the world's history) are each characterised by its own peculiar fossils, or facies of animated existence. Thus, when tabulated, these systems and groups present the following chronological arrangement :—

Such are the main stages into which geologists have ar

ranged the stratified crust of the globe-the great chapters, as it were, of world-history, whose strata, like the leaves of a mighty volume, are indelibly stamped with the forms and characters of extinct vitality. As in human history we speak of the times of Ninevites, Egyptians, Greeks, and Romans, so in geology we refer to Silurian, Devonian, Carboniferous, and other systems; and as Ninevites and Egyptians present a certain similarity or facies of civilisation, and Greeks and Romans another, so we unite certain systems, having features in common, into Palæozoic, Mesozoic, and Cainozoic epochs. As to the Time represented by these groups and systems, we have at present no means of determining; but, gauging the past by the present rate of geological change, the amount must be immense, and we could no more form an idea of its aggregate-even could we express it in years and centuries-than we can form a conception of the distances that separate our globe from the remoter stars of the universe. Enough for us, in the mean time, to be convinced of the vastness of its relative portions, and to fix with certainty the order of their occurrence. As in human history it is ever more important to determine the true sequence and connection of events than to be curious about the minutiae of dates, so in geology it is far more satisfactory to discover the order in time than to indulge in surmises about the expression of its duration in years and centuries. It is surely of higher value to be able to determine the relative ages of two contiguous deposits, the contemporaneity of others widely apart, and the kind and character of life they respectively imbed, than to perplex ourselves with vague hypotheses as to the number of years that have passed since the date of their deposit. And yet even for this, too, the time will undoubtedly arrive! Geological events are the orderly results of natural laws; laws are as fixed in their times as in their modes of

action; and while the Creator has permitted the human intellect to investigate and determine the one, we may rest assured that the same intellect is yet destined to discover the amount and duration of the other. In the mean time, all that geology attempts is to arrange the formation of the earth's crust into so many provisional stages—each stage representing an indefinite amount of time, but embracing such stratified deposits as indicate a contemporaneity of origin, and are characterised by a general similarity of organic remains. In this case, each stage represents the sediments of a certain period, and is necessarily characterised by its own peculiar fossils-every change of sea and land not only giving rise to new sediments, but to altered conditions of vital existence, that are inevitably followed by a modification of the flora and fauna. And summing up the whole, we are presented with the outline, at least, of a grand and continuous evolution of vitality. Here there may be local imperfections in the record there the characters may be fragmentary and obscure; but in the main the broad features of world-history are sufficiently obvious, and these systems and formations (provisional as they may be) enable the geologist to give intelligible expression to the line and order of occurrence.

Proceeding upon the basis of this arrangement, let us now inquire into the nature of the Plants and Animals preserved in these successive formations. Were they constructed on the same plan, and destined to perform analogous functions in the economy of nature, with those that now live and flourish around us? Or if differing in type, what the amount of that difference, and the presumable function which that difference implies? If race after race has come and departed, what the conditions that accompanied their advent, and what the causes which apparently

lead to their extinction? Do the simpler and lowlier forms always precede the higher and more complex; and does the introduction of any family in point of time harmonise with its place in the scale of organisation? Does the extinction of species appear to be, in every case, the result of a change in external conditions; or may not species, like individuals, have a term assigned to their existence from the beginning? If race after race follow each other in order of organisation, what countenance does this give to the theory of self-development? Is there, as far as palæontology can discover, any foundation whatever for the belief in a progressive transmutation of species, by which the lower gives birth to the higher; or does geology not rather establish the conviction of independent creations as time rolled on and new conditions were prepared for their reception? Seeing that physical phenomena invariably take place under the orderly operations of natural laws, are we, in the spirit of sound philosophy, entitled to assume for vital phenomena any other mode of occurrence? In all other reasonings are we to adopt the inductive method, and in the solitary instance of LIFE-its incomings and outgoings-are we to forsake this course as impotent and unavailing, and appeal to the direct and miraculous interference of Creative Power? These, and numerous analogous questions, present themselves to the palæontologist; and if in human history chronologers are often disagreed as to times and incidents so recent as those that come within the range of a few thousand years, if ethnologists have failed to trace with certainty the relationship of the few varieties of our own race, and antiquarians be only beginning to decipher the phases of certain extinct civilisations, what marvel need it be that geologists are not yet as one as to events for which time has no dates, save "cycles" and "systems," or that they should be occasionally unable to discover the

nature and functions of creatures whose remains are so fragmentary, and to whom existing nature offers not a single specific identity? And yet, as we shall afterwards see, geological belief is much more uniform than is generally supposed; and, founding on this belief, palæontology has been enabled, within the brief space of half a century, to establish a history of the world's Past Life, more marvellous by far than the fabled creatures of romance, and yet so true that he who remains in ignorance of its facts can never hope to attain to a satisfactory knowledge of the scheme of life that at present surrounds us.