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supposed that in strata so eminently marine, we are likely to discover more than the merest indication of a terrestrial vegetation. Still we can only reason from what we know, and shape our inferences by the results of our observation.

When we turn to the Fauna of the system, we find the record much more complete and legible. We are presented with infusorial organisms from its shales; graptolites or sertularian-like zoophytes in inconceivable numbers; corals of

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1. Oldhamia: 2, Protcv.rguiaria; 3, Graptclites: 4, 5, Diplograpsus 6, Didymograpsus: 7, Rastrites.

many genera and species; encrinites of various forms; star-fishes, independent and free-floating; and sea-urchinlike cystidea, attached to the sea-bottom by their jointed foot-stalks. In molluscan life we have representatives of every order brachiopods, acephalans, gasteropods, pteropods, and cephalopods - vegetable-feeders thronging the shores, carnivorous orders in the open sea, and infusorialfeeders in the deeper waters. The great preponderance of brachiopods over acephalans and gasteropods is one of the most noticeable features in the molluscan life of the period -a feature now reversed, seeing that acephalans and gas

teropods are the predominating forms in existing waters.* In the articulate division we have numerous annelid markings-the trails and burrows of sea-worms; the calcareous crusts and shell-like cases of serpula and spirorbes; and a vast and characteristic display of trilobites (three-lobed), a form of crustacean almost restricted to the period; together with the larger and higher forms of eurypterites (broadfins-in allusion to their paddle-like swimming limbs). These

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1. Heliolites; 2, Catenipora; 3, Cyathophyllum; 4, Taxocrinus; 5, Cystidea; 6, Palæaster

trilobites, along with some smaller bivalved forms of crustacea, have been long and familiarly known; but the euryp

* We abstain, in this as in other instances of comparison, from numerical tabulations, as every year of further discovery and nicer discrimination of species disturbs, if not destroys, the value of such statistics. Not many years ago the Brachiopoda were supposed to be on the very verge of extinction, and yet the application of the dredge to deeper waters has revealed the existence of nearly a dozen genera in modern seas. Every year, too, discovery adds some new form to our lists of fossils, while former lists of so-called species-Continental, British, and American-are being examined with more rigorous care, and reduced to their proper value.

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2. Linguia; 2, Rhynconella: 3, Pentarnerus; 4, Strophomeua; 5, Spirifer: 6, Murchisonia; 7, Orthoceras; 8, Lituites; 9, Maclurea.

beds of the system, and two of the most abundant genera

5

SILURIAN CRUSTACEA-TRILOBITES.

1, Phacops; 2, Trinucleus; 3, Ampyx; 4, Ogygia; 5, Ilænus; 6, Calymene;
7, Calymene coiled up.

are here for the first time restored with something like accuracy and life-like proportions. As already hinted, the remains of fishes are but sparingly found in the uppermost beds of the system; and it is still an open question with

2

SILURIAN CRUSTACEA-EURYPTERITES.

1, Pterygotus Acuminatus; 2, P. Bilobus; 3, Ceratiocaris (bivalved Crustacean).
From the Upper Silurian or Passage Beds of Lanarkshire.

geologists, whether these are to be viewed as marking the close of the silurian or the dawn of the devonian epoch. For our own part, we accept them as part and parcel of the silurian fauna; and though negative evidence forbids us in the meanwhile to enter on our lists the remains of insects, reptiles, birds, and mammals, there is nothing that militates against the likelihood of their occurrence. On the contrary, all analogy favours the supposition that the great types of life-radiate, molluscan, articulate, and vertebrate-were from the beginning contemporaneous on our globe, and that it is to the minor modifications of the type, and not to the type itself, we are to look for that gradation and progress

which marks the geological periods. In this opinion we are further fortified by the decidedly expressed conviction of one of the ablest investigators of the present age. "However much naturalists may still differ in their views regarding the origin, the gradation, and the affinities of animals," says Professor Agassiz in his Essay on Classification, "they now all know that neither radiata, nor molluscs, nor articulata have any priority one over the other as to the time of their first appearance upon earth; and that, though some still maintain that vertebrata originated somewhat later, it is universally conceded that they were already in existence towards the end of the first great epoch in the history of our globe. I think it would not be difficult to show, upon physiological grounds, that their presence upon earth dates from as early a period as any of the three other great types of the animal kingdom, since fishes exist wherever radiata, molluscs, and articulata are found together, and the plan of structure of these four great types constitutes a system intimately connected in its very essence. Moreover, for the last twenty years every extensive investigation among the oldest fossiliferous rocks has carried the origin of vertebrata step by step farther back; so that, whatever may be the final solution of this vexed question, so much is already established by innumerable facts, that the idea of a gradual succession of radiata, molluscs, articulata, and vertebrata, is for ever out of the question."

Here, then, in the silurian system we find nothing abnormal or marvellous! Its sediments tell of seas whose shores, in favourable localities, were clad with weeds, and whose waters were thronged with zoophytes, star-fishes, sea-urchins, shell-fish, and crustacea. Plant-feeder and animal-feeder start simultaneously in the race of life; and it requires no great stretch of fancy to repeople silurian waters, busy and joyous on a summer's eve as the tribes

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