kingdom. And it is curious to learn that, unknown in the earlier eras, and just beginning to make their appearance in the secondary epochs, they come into full force and vigour in the tertiary and post-tertiary—the periods at which the higher animals and man are present to reap the advantages of their more varied utilities.

Such are the leading features of the great groups of the vegetable kingdom-groups to which we shall have frequent occasion to allude when we come to treat the successive stages of the fossil flora, and which are here displayed in pictorial outline with a view to facilitate the comprehension of these allusions. Though thus arranged in physiological groups, the whole, from the simple cell that floats on the putrid pool to the noblest tree of the forest, forms but one orderly and co-adjusted system; and could we combine the extinct with the living, the same order and co-adjustments would be found to run as unswervingly through the wider combination. The conception is one, though its expression through time and space must necessarily assume the character of infinite diversity.

Subdividing still further, according to their most marked characteristics, whether external or internal, the botanist arranges all the forms of vegetable life into some 60 or 70 orders, about 300 genera, and upwards of 100,000 species. As most of these distinctions, however, are founded on the form and connection of the flower, fruit, and leaf— organs which rarely or never occur in intelligible union and preservation in a fossil state-the palæontologist is guided in the main by the great structural distinctions already adverted to, and not unfrequently by the simple but unsatisfactory test of "general resemblance." On the whole, Fossil Botany, or Palæophytology, as it is sometimes termed, is by no means in a satisfactory state, and the science languishes for the advent of some master minds to do for

it what Cuvier and Agassiz and Owen have done for the sister science of Fossil Zoology.

Notwithstanding the fragmentary state of the plants that turn up to the geologist, the greatly altered conditions of the parts that are found, and the hopelessness of ever discovering the legible dispositions of such evanescent portions as the floral organs, on which so much of existing botany is founded: notwithstanding all these obstructions, there is still so much remaining-the structure of the roots, stems, barks, leaves, fronds, and fruits-the characteristic markings of their different surfaces—and the scars which their parts leave on separation—that the competent botanist, armed with his microscope and ample means of comparison, should have little difficulty in arriving at many definite and important conclusions. The anastomosing disposition of a sea-weed. is surely sufficiently distinct from the branching aspect of a terrestrial plant-the reticulate venation of a dicotyledonous leaf from the parallel arrangement of a monocotyledon -the scalariform tissue of a fern from the punctated tissue of a conifer-and the bundled mass of an endogenous stem from the concentric layers of an exogen. These and many other characteristics are sufficiently preserved in the strata of every formation; and though we may not be enabled to say, on the principles of existing botany, that this fragment is that of a cruciferous plant, and that of a leguminous one, we have, at all events, enough to fix in the mean time the great progressional order of plant-life from the predominance of Acrogenous orders in primary formations to the higher Gymnosperms of the secondary, and from these again to the still higher Angiosperms of the tertiary and current epochs. And Geology, strong in the faith of Nature's unity and persistency of plan, rests assured, that under right. methods of research the key to that Plan will yet be dis

covered, enabling the palæontologist to unfold the relations of fossil plant-life, its distribution in space, and its progress in time, even as the botanist now determines its existing relationships, and maps out its centres and areas of geographical arrangement.

2.-ITS FAUNA OR ANIMAL LIFE.

As with plants, so with animals. While we find them everywhere on the earth, in the air, and in the waterson the substances of plants, and even in the living tissues of other animals-they are as imperatively governed by the influences of climate, food, and other external conditions as the Vegetable world, though possessed for the most part of a locomotion which at first sight might seem to confer on them an ubiquity of habitat. Thus, the FAUNA of the tropics is essentially different from that of the temperate zone, and the animals which people the temperate zone have but little in common with those of the arctic regions. It is true that some, like Man and his companions, the dog, horse, and other domesticated animals, have a range all but universal; but generally speaking, the zones of Animal Life-horizontally and vertically-are about as sharply defined as those of vegetation. The elephant and rhinoceros that luxuriate in the low tropical jungle would fare but indifferently on the lofty slopes of the Himalayas; while the buffalo and bison which herd at these heights would cease to exist were they raised but a few thousand feet higher. As with altitude on land, so with depth in the ocean; and thus the sea-weeds and shells that grow and live within the influence of the tides constitute a Littoral zone very different from the Laminarian or broad sea-tangle zone which extends, in British seas, from 40 to 90 feet in depth; this again is

essentially distinct from the Coralline zone, which ranges from 90 to 300 feet, and is the great theatre of marine life; while beyond this lies the Coral zone, the region of the strong calcareous corals extending from 300 to 600 feet in depth from the shore line. But it is not alone to climate and external conditions that we must look for the variety and distribution of animal life. There is an aboriginal diffusion of different tribes and families from certain centres and over certain areas, for which science can as yet offer no satisfactory reason. Thus, why should the giraffe, or ostrich, or hippopotamus, be restricted to the continent of Africa, while the forests, and plains, and river-swamps of South America enjoy the same tropical sun, and seem every way equally adapted to identity of vitality? The pampas of America, as has been proved by experience, are as well fitted for the increase of the horse as the plains of Europe or the steppes of Tartary; and yet, till man carried him. thither a few hundred years ago, no horse of the current epoch existed there. The ornithorhynchus burrows only in the river banks of Australia; the apteryx is unknown beyond the limits of New Zealand; the sloth is confined to the tropical forests of America; the armadillo to the same region; and not one of the Old World monkeys is identical with any of those of the New. Nor is it alone the terrestrial tribes that are thus limited and restricted; the aërial and aquatic, though possessing superior facilities for dispersion, are equally circumscribed, each within its own geographical habitat. The humming-birds flutter only over the flowers of the New World; the pheasants are unknown beyond the coverts of the Old; the shark-like cestraciont frequents alone the waters of the Southern Pacific; and the trigonia never carries its shell beyond the shores of Australasia. Such restrictions we cannot explain unless by ascribing them to independent centres of creation,

or to means of distribution that prevailed during former geological epochs, but which ceased to exist when sea and land received their present relations. And this brings us to remark on what are termed by zoologists the law of identity and the law of representation; that is, that different regions, though not peopled by identical species, may be peopled by animals which perform analogous functions, and represent them, as it were, in the great plan of vital economy. Thus, the ostrich of Africa is represented in South America by its congener the rhea; the jaguar and puma of the New World represent the tiger and lion of the Old; the camel of Arabia finds its analogue in the llama of Peru; and similar functions are at once discharged by the gavial of the Ganges, the crocodile of the Nile, and the alligator of the Amazon. Over and above these physical relationships there is also that which has reference to the size of the animal, and the element in which it is destined to live. As a general rule, and each within its own order or family, the aquatic members are larger than the terrestrial; the amphibious bulkier than those that are strictly terrestrial; the marine superior in size to those of fresh-water habitat ; and the terrestrial more massive than the arboreal. Admitting these relations, and reasoning from the present to the past, the comparative bulk of organic remains may often become an index to external conditions of life, and throw light over the investigations of the paleontologist, when other indications are uncertain and obscure.

Besides these distinctions and restrictions imposed on vitality by external conditions, there are those connected with the functions they have to perform in the economy of nature. Some, for instance, are fitted to live on a purely vegetable diet, others to prey on the flesh of other creatures; some are constructed so as to feed only on seeds and grains, others to prey solely on insects; many earn their subsist