-fickle and uncertain as these may seem-but is the result, immediate and remote, of Law, could we only grasp the multifarious conditions that are connected with its production. In tracing, then, the Flora and Fauna of successive epochs, as far as the limits of a popular sketch will permit, we can only indicate a few of their more prominent features and the laws that seem to bear on their development; and yet, restricted as these limits are, enough, we trust, will be indicated to arrest the attention and to arouse the interest in the further prosecution of a subject that stands second to none on the roll of human acquirements. And, after all, it is better to be imbued with the right spirit of research, and to be impressed with the conviction. of the universality and uniformity of natural law, than to have the mind bewildered with details which it cannot connect, and for whose occurrence in nature it is altogether unable to render a reason.

And, first, we enter on what has been termed the PALEOZOIC or "Ancient-Life" period of the world—a period embracing the Silurian, Devonian, Carboniferous, and Permian formations, and characterised, as far as geological evidence goes, by the almost total absence of a dicotyledonous flora, by a preponderance of invertebrate life, and by the general absence of the higher vertebrata, as reptiles, birds, and mammals. The lowest in rank seem the earliest in time; and so in this primeval epoch, cryptogams and cold-blooded water-breathers become the leading manifestations of vitality. The strata lying beneath the Paleozoic (as will be seen by a reference to the Geological Record) have been termed the Azoic or "void of life;" but, more correctly and philosophically, the HYPOZOIC, which merely indicates their position "beneath" the fossiliferous strata, and that without asserting them to be wholly desti

tute of organic remains. So far as our present purpose is concerned, it matters little which term is adopted, so long as we bear in mind that up to the present day they have yielded no traces of life, and are to all intents and purposes truly Azoic. That the Crystalline or Metamorphic strata, termed clay-slate, mica-schist, and gneiss, were at one time the clayey, sandy, and limy deposits of seas and estuaries, is at once admitted by every competent geologist; and that if these seas contained life, those strata must have imbedded its remains. But then, these deposits have, since their solidification into rock, been subjected to thermal, chemical, electrical, and other agencies, to such a degree that they have been converted, or metamorphosed, into crystalline masses, and every trace of life has been obliterated from their structure. No doubt it has been ingeniously suggested that the occurrence in metamorphic rocks of sulphuret of iron, of phosphate of lime, bituminous springs, and other similar products, gives evidence of the presence of organic bodies, through the medium of whose decay such compounds were eliminated. On the other hand, experimentalists equally ingenious have assigned to these products a purely chemical origin; and, even if they could not, the geologist would be little aided by a contrary hypothesis, so long as he had no trace of organic form or texture to guide him in his deductions.

To the paleontologist, therefore, the CAMBRIAN period, with its obscure and scattered zoophytes, trilobites, and shells, becomes the so-called "Dawn of Life." He knows of nothing beyond this primordial zone, and the spirit of true philosophy forbids him to substitute conjecture for fact, or hypothesis for reality. It may gratify the cosmogonist to fashion a glowing globe by the condensation of nebular masses, to cool by radiation a solid crust on the glowing orb, and, after ages of chaotic confusion, to plant

the germ of life on some sunny and serene spot ;-it may charm the materialist to claim for Life the eternity he does for Matter, by referring to a metamorphism which is continuously obliterating the fossils in the deepest seated rocks; but the paleontologist is debarred from such reveries, and is bound down by a rigid chain of facts as they occur in nature. He has traced life so early as the Cambrian slates; should it be detected still lower, he is ready to accept it. To him, in the mean time, the Metamorphic schists are a tabula rasa; the Cambrian slates form his furthest verge and boundary; and the spirit of induction restrains him within its limits. And, after all, fossil evidence itself is greatly in favour of the view, that we have here attained, or all but attained, the furthest limit of life. We see it increasing and spreading into higher and higher forms as we ascend in the geological scale, and decreasing and narrowing into lowlier forms as we descend: numerically the forms are fewer, physiologically they become less important; and it is but fair induction to believe that in the few scattered forms of Cambria we have all but reached the zero of organic existence."

From the Cambrian the palaeontologist passes into the Silurian age-a period characterised by its lowly sea-weeds and doubtful traces of land plants-by genera and species of protozoan, radiate, molluscoid, molluscan, and articulate types, but by few, if any, even of the lowest vertebrate order. Its strata consist of shales, sandstones, conglomerates, and limestones-the solidified muds, sands,

* It is right to mention, however, that the tendency of recent discovery is to carry the traces of life further and further back among these slaty and semi-crystalline strata. The detection of new graptolites and trilobites in the schists of Bray Head, Skiddaw, Bohemia, and North America, is a fact too significant to be overlooked in geological speculation.

F

pebbles, and coral-growths of seas and estuaries. It is customary for a certain class of geologists to talk of "the deep, turbid, and shoreless seas of the Silurian epoch, as if the globe was then enveloped by one dreary monotony of ocean. Do such generalisers ever for a noment think that such a vast thickness of sediments could never have been produced without the existence of broad lands from which they were transported by rivers, or of sea-shores from which they were abraded by waves and tidal currents? Could conglomerates be formed without wave-exposed beaches, sands without open sea-shores, or could shells that are truly littoral, and corals that flourish only from twenty to sixty fathoms, have existed without water of limited depth for their development? The eye of the trilobite would have been useless in a turbid ocean; a turbid ocean would have been death to the growth of corals; worm-burrowed, ripple-marked, and rain-pitted sandstones could have been formed only on shores exposed to the alternate ebb and flow of the tide; and conglomerates are merely the broken-down and water-worn fragments of an older rocky shore. In fine, there is not a single feature in the rocks of the Silurian period which might not take place in the ocean of our own day. The existence of deeper and shallower seas— —of waves, currents, tides-of lands, shores, and rivers of sunlight, and rains, and winds-are as clearly impressed on its strata as they are upon those of every other geological epoch. It differs alone in the geographical distribution of its sea and land-the greater insularity, perhaps, of the land-masses—their consequent climatology— and the specific characters of its plants and animals; though, knowing the wide extent of its deposits (and they occur alike in the continents of the Old and New World, in the northern and in the southern hemisphere), geology is not yet in a position to map with accuracy the geography of the

period, nor to define with certainty the external conditions to which its flora and fauna would be necessarily subjected.

When we turn to its biological aspects, the outline, though far from complete, is at least, as far as it goes, homogeneous and intelligible. Fucoids or fucus-like seaweeds, some carbonaceous fragments of unknown stems, spore-like organisms, apparently from land plants, and a few lepidodendroid twigs that may have belonged to some ancient form of club-moss, are nearly all we know of the silurian Flora; though, judging from the extent of anthracite deposits in various regions, vegetation (aquatic and terrestrial) must in certain centres have existed in some

1

FRAGMENTS OF SILURIAN FLORA.

1. 2, Fucoids-Cruziana and Chondrites ?); 3, 4, Lycopodites-Lepisodendroid twigs from the Upper Silurians of Lanarkshire.

exuberance. On the whole, the silurian Flora is of a very lowly character, and its scanty fragments find their nearest affinities in the sea-weeds, liver-worts, and club-mosses of existing nature. Of course, the imperfection of the geological record is fully and frankly admitted, for it cannot be