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seen, rising or leaning over on their short and slender stems, the simple forms of the crinoids or stoneflowers, more beautiful, perhaps, and more picturesque than the sea-anemones of our own coast, even when these latter are seen in all their beauty, and with their tendrils and fibres widely expanded and brilliantly coloured. The crinoids, wanting indeed the colour, but of far more elegant form, would some of them be seen spreading out their arms and fingers in search of prey, while others closed entirely their cuplike envelope,-giving a variety and life to the sea bottom, in spite of the cold, hard, stony frame-work of the animal, scarcely concealed by a living coat of leathery integument.
Besides these, and sometimes attached to them, every hard fragment of rock, and every hard surface at the bottom of the sea, at all moderate depths, would doubtless be overgrown with some one or other of the numerous family of Brachiopoda (Trilobites, &c.), which we know to have been abundant. A few of the Conchifera (Pectens, &c.), with their bivalve shells, might also be seen flitting about in the water, moving by jerks produced by the sudden shutting of their valves, but an infinite number and variety of other animals, swimming with much greater freedom and elegance, and of far greater size, then crowded the ocean, rising and sinking at pleasure, and with great facility. Some of these were of formidable dimensions, exhibiting a strange spear-like tail projecting downwards, and terminating above in a more or less powerful and sack-like body, moving with infinite rapidity in every direction; while others, short and almost globular, were perhaps less
active, and sought their food in the little bays and inlets.
But there were then no fishes: these Cephalopoda were the lords and tyrants of that creation; they were the most numerous, the most highly organized, the least defended by stony or scaly armour, and the most powerful. Their long shell was probably not meant to shelter them from danger, and their whole appearance and character indicates that they were the attackers-not the attacked, and, like other powerful animals, were unprovided with defensive weapons, their vigour, strength, and activity answering this purpose sufficiently.
It is not for us to calculate how often our globe performed its annual course in the heavens between the commencement and the close of the long period which we have been considering in this chapter. We may conjecture, indeed, from the evidence before us in the fossil remains, and the order and condition in which they occur, that these revolutions must be counted rather by tens of thousands than by units; for during this lapse of time, whatever it may have been, many thousand feet of deposits were formed in various parts of the bottom of the sea, and each succeeding deposit, though only of a few inches, is provided with its own written story, its sacred memoranda, assuring us of the regularity and order that obtained, and of the perfect uniformity of plan. The changes that took place during this time were gradual and successive; the world of water was then being prepared, slowly but surely, for the reception of more highly organized beings, and, at length, although there is little appearance of physical alteration, the
increasing abundance of these animals marks the commencement of a new period.
It is interesting to contemplate the probable conditions of the earth's surface and its physical features, as made known to us by these fossil remains; but in doing so, we ought to bear in mind constantly the true nature and value of the evidence. So far as it is positive—so far as we have only to make out the meaning of what we see-this is not difficult or doubtful; but when we begin to draw general conclusions, and speak of the absence of whole groups, because we do not discover any indications of their existence, we are reasoning from our own view of what, in all probability, and according to analogy, occurred, and not from positive data. Still, as the circle of our knowledge expands, and these conclusions, being tried by the test of experience, are found still correct, they do assume more and more the character of true generalisations, and become at length admitted as truths. I have here, and elsewhere in these pages, endeavoured to give fairly the result of all the evidence at present obtained on the subject, and have usually intimated the existence of a doubt where the amount of evidence seemed to me insufficient.
INTRODUCTION OF FISHES, THE CHARACTERISTIC ANIMALS OF
Ir would seem that, during the whole period of the deposit of those many thousand feet of strata which make up the silurian series in Wales, Cumberland, and other parts of the world, there was no contemporaneous formation going on in the district now occupied by Scotland, or in that which at present forms the south-western counties of Cornwall and Devonshire in England. Further south, however, the silurian rocks are met with again, as in Brittany; and, as I have already mentioned, they exist in great abundance in various parts of Scandinavia, but owing to some cause, probably because those portions of the earth were then elevated above the level of the sea, and so were not capable of receiving any extensive additions, there does not appear to be in the British islands any regular and complete passage from the slates and sandy beds of the older and non-fossiliferous period, to similar deposits immediately resting upon them. In Belgium, Russia, and Germany, such a continuity may be traced.
The existence of a break in the continuity of strata occurring thus early, and extending over an important geological period, but evidently local and confined to a small district, is a phenomenon well worthy of remark,
and one which, when understood, will perhaps clear up many difficulties which have sometimes puzzled Geologists; but, before offering this explanation, it should be understood distinctly what is meant by calling an event of this kind a break in the continuity of strata or groups of strata.
If the animated beings who inhabit the different parts of the earth and sea had been at all times the same; if it were an indifferent thing to the marine animals whether they dwelt in shallow water, near shore,—in the deeper water of bays and other sheltered places,―in the open sea, near the surface, and where exposed to the constant action of the tides and currents, or in the great depths of the ocean, far removed from land; and if species, thus cosmopolitan in their habits, had been introduced at the first creation of animals on the earth, and had succeeded one another in the regular order of nature, generation after generation repeating the same species; then, indeed, it would have been difficult, and often impossible, to determine whether the various strata lying over one another in any given spot were formed by continuous deposits, or with intervals between them of sufficient magnitude to allow of the interpolation of other beds in other places. But these conditions do not obtain in nature. It is well known to the naturalist, that, although some animals are much more capable of adapting themselves to changing circumstances than others, all species are more or less limited in their range, and that, in a vast proportion of cases, they are very strictly limited; a change of a few yards in the depth of the water, an alteration in the nature of the sea bottom or in the degree of exposure to tidal action,