HKB
of the river abated, marine shells of the genera Trigonia, Turritella, Pecten, etc., established themselves in the same area, and plants allied to Zostera and Fucus grew on the bottom.
The fossil plants of this member of the upper chalk at Aix have been diligently collected and studied by Dr. Debey, and as they afford the only example yet known of a terrestrial flora older than the Eocene, in which the great divisions of the vegetable kingdom are represented in nearly the same proportions as in our own times, they deserve particular attention. Dr. Debey estimates the number of species as amounting to more than two hundred, of which sixty-seven are cryptogamous, chiefly ferns, twenty species of which can be well determined, most of them being in fructification. The scars on the bark of one or two are supposed to indicate tree-ferns. Of thirteen genera three are still existing, namely, Gleichenia, now inhabiting the Cape of Good Hope, and New Holland; Lygodium, now spread extensively through tropical regions, but having some species which live in Japan and North America; and * Asplenium,* a cosmopolite form. Among the phænogamous plants, the Conifers are abundant, the most common belonging to a genus called Cycadopteris by Debey, and hardly separable from Sequoia (or Wellingtonia), of which both the cones and branches are preserved. When I visited Aix, I found the silicified wood of this plant very plentifully dispersed through the white sands in the pits near that city. In one silicified trunk 200 rings of annual growth could be counted. Species of Araucaria like those of Australia are also found. Cycads are extremely rare, and of Monocotyledons there are but few. No palms have been recognised with certainty, but the genus Pandanus, or screw pine, has been distinctly made out. The number of the Dicotyledonous Angiosperms is the most striking feature in so ancient a flora.[3]
Among them we find the familiar forms of the Oak, Fig, and Walnut (Quercus, Ficus, and Juglans), of the last both the nuts and leaves; also several genera of the Myrtaceæ. But the predominant order is the Proteaceæ, of which there are between sixty and seventy supposed species, many of extinct genera, but some referred to the following living forms—Dryandra, Grevillea, Hakea, Banksia, Persoonia—all now belonging to Australia, and Leucospermum, species of which form small bushes at the Cape.
Brongniart. Lindley. Cryptogamic. 1. Cryptogamous amphigens, or cellular cryptogamic. Thallogens. Lichens, sea-weeds, fungi. 2. Cryptogamous acrogens. Acrogens. Mosses, equisetums, ferns, lycopodiums,—Lepidodendra. Phænerogamic. 3. Dicotyledonous gymnosperms. Gymnogens. Conifers and Cycads. 4. Dicot. angiosperms. Exogens. Compositæ, leguminosæ, cruciferæ, healths, etc. All native European trees except conifers. 5. Monocotyledons. Endogens. Palms, lilies, aloes, rushes, grasses, etc.
The epidermis of the leaves of many of these Aix plants, especially of the Proteaceæ, is so perfectly preserved in an envelope of fine clay, that under the microscope the stomata, or polygonal cellules, can be detected, and their peculiar arrangement is identical with that known to characterise some living Proteaceæ (Grevillea, for example). Although this peculiarity of the structure of stomata is also found in plants of widely distant orders, it is, on the whole, but rarely met with, and being thus observed to characterise a foliage previously suspected to be proteaceous, it adds to the probability that the botanical evidence had been correctly interpreted.
An occasional admixture at Aix-la-Chapelle of Fucoids and Zosterites attests, like the shells, the presence of salt-water. Of insects, Dr. Debey has obtained about ten species of the families Curculionidæ and Carabidæ.