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Updated: May 24, 2025
The vertebrates first make their appearance, in the shape of fishes, towards the close of the Silurian period, the second of the great geological epochs.
Who is it? well may be asked. What name is it that blanches with terror the cheeks of the Patagonian navy? Who but the Pirate Prodigy the relentless Boy Scourer of Patagonian seas? Voyagers slowly drifting by the Silurian beach, coasters along the Devonian shore, still shudder at the name of Bromley Chitterlings the Boy Avenger, late of Hartford, Connecticut.
Thus the views previously entertained regarding the invertebrate character of the fauna of the Silurian epoch, have ultimately remained unaffected, so far as these Potsdam slabs are concerned. Slabs of sandstone and shale often retain what is called the ripple-mark that is, the corrugation of surface produced by the gentle agitation of shallow water over sand or mud.
Between the Carboniferous and Silurian strata there intervenes, in the United States and Canada, a great series of formations referable to the Devonian group, comprising some strata of marine origin abounding in shells and corals, and others of shallow-water and littoral origin in which terrestrial plants abound.
For all the species of the same group, however long it may have lasted, are the modified descendants one from the other, and all from a common progenitor. In the genus Lingula, for instance, the species which have successively appeared at all ages must have been connected by an unbroken series of generations, from the lowest Silurian stratum to the present day.
For instance, it cannot be doubted that all the Cambrian and Silurian trilobites are descended from some one crustacean, which must have lived long before the Cambrian age, and which probably differed greatly from any known animal.
If there were any harmony between the Miltonic account and the circumstantial evidence, we ought to have abundant evidence of the existence of birds in the Carboniferous, the Devonian, and the Silurian rocks. I need hardly say that this is not the case, and that not a trace of birds makes its appearance until the Tar later period which I have mentioned.
The decomposition of the spores has made the shales highly bituminous, and the oil and gas have accumulated in the reservoirs of overlying porous sandstones. INVERTEBRATES. We must pass over the ever-changing groups of the invertebrates with the briefest notice. Chain corals became extinct at the close of the Silurian, but other corals were extremely common in the Devonian seas.
The several difficulties here discussed, namely our not finding in the successive formations infinitely numerous transitional links between the many species which now exist or have existed; the sudden manner in which whole groups of species appear in our European formations; the almost entire absence, as at present known, of fossiliferous formations beneath the Silurian strata, are all undoubtedly of the gravest nature.
Murchison and De Verneuil discovered this species dispersed in myriads through a white limestone of Upper Silurian age, on the banks of the Is, on the eastern flank of the Urals in Russia, and a similar species is frequent in Sweden. Lingula Lewisii, J. Sowb. Atrypa reticularis, Linn. Upper valve. b. Lower valve. c.
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