OLDHAMIA ANTIQUA;—the oldest known Zoophyte.
Wrae Head, Ireland.
PALÆOCHORDA MINOR.
(One half nat. size.)
Beginning with the plants, let us, however, remark, that they do not precede in the order of their appearance the humbler animals. No more ancient organism than the Oldhamia of the Lowest Irish Silurians, a plant-like zoophyte somewhat resembling our modern sertularia, has yet been detected by the geologist; though only a few months ago the researches of Mr. Salter in the ancient rocks of the Longmynd, Shropshire, previously deemed unfossiliferous, have given, to it what seem to be contemporary vegetable organisms, in a few ill-preserved fucoids. So far as is yet known, plants and animals appear together. The long upward march of the animal kingdom takes its departure at its starting point from a thick forest of algæ. In Bohemia, in Norway, in Sweden, in the British Islands, in North America, wherever, in fine, what appears to be the lowest, or at least one of the lowest, zones of life has yet been detected, the rocks are found to be darkened by the remains of algæ, so abundantly developed in some cases, that they compose, as in the ancient Lower Silurians of Dumfriesshire, impure beds of anthracite several feet in thickness. Apparently, from the original looseness of their texture, the individual plants are but indifferently preserved; nor can we expect that organisms so ancient should exhibit any very close resemblance to the plants which darken the half-tide rocks and skerries of our coasts at the present time. We do detect, however, in some of these primordial fossils, at least a noticeable likeness to families familiar to the modern algæologist. The cord-like plant, Chorda filum, known to our children as "dead men's ropes," from its proving fatal at times to the too adventurous swimmer who gets entangled in its thick wreaths, had a Lower Silurian representative, known to the Palæontologist as the Palæochorda, or ancient chorda, which existed apparently in two species,—a larger and smaller. The still better known Chondrus crispus, the Irish moss or carrageen of our cookery-books, has likewise its apparent though more distant representative in Chondritis, a Lower Silurian algæ, of which there seems to exist at least three species. The fucoids, or kelp weeds, appear to have had also their representatives in such plants as Fucoides gracilis of the Lower Silurians of the Malverns; in short, the Thallogens of the first ages of vegetable life seem to have resembled, in the group, and in at least their more prominent features, the algæ of the existing time. And with the first indications of land we pass direct from the Thallogens to the Acrogens,—from the sea weeds to the fern allies. The Lycopodiaceæ;, or club mosses, bear in the axils of their leaves minute circular cases, which form the receptacles of their spore-like seeds. And when, high in the Upper Silurian System, and just when preparing to quit it for the Lower Old Red Sandstone, we detect our earliest terrestrial organisms, we find that they are composed exclusively of those little spore receptacles. The number of land plants gradually increases as we ascend into the overlying system. Still, however, the Flora of even the Old Red is but meagre and poor; and you will perhaps permit me to lighten this part of my subject, which threatens too palpably to partake of the poverty of that with which it deals, by a simple illustration.
| Fig. 7. LYCOPODIUM CLAVATUM. | Fig. 8. EQUISETUM FLUVIATILE. |
We stand, at low ebb, on the outer edge of one of those iron-bound shores of the Western Highlands, rich in forests of algæ, from which, not yet a generation bygone, our Celtic proprietors used to derive a larger portion of their revenues than from their fields and moors. Rock and skerry are brown with sea weed. The long cylindrical lines of Chorda filum, many feet in length, lie aslant in the tideway; long shaggy bunches of Fucus serratus and Fucus nodosus droop heavily from the rock sides; while the flatter ledges, that form the uneven floor upon which we tread, bristle thick with the stiff, cartilaginous, many-cleft fronds of at least two species of chondrus,—the common carrageen, and the smaller species, C. Norvegicus. Now, in the thickly-spread fucoids of this Highland shore we have not a very inadequate representation of the first, or thallogenic vegetation,—that of the great Silurian period, as exhibited in the rocks, from the base to nearly the top of the system. And should we add to the rocky tract, rich in fucoids, a submarine meadow of pale shell sand, covered by a deep green swathe of zostera, with its jointed saccharine roots and slim flowers, unfurnished with petals, we would render it perhaps more adequately representative still.
