OCR Text |
Show 100 FOSSIL COAL PLANts. whether of mammalia, reptiles, or ~esta:ea, :re scarcely in any instance identifiable with any now m bemg . In these stra.ta, whether they were formed in seas or lakes, w.e find the remams of many animals, analogous to those of hot chmates, such as the cr.o co d!'le , turtle , and tortoise ' and many large she.l ls of the. genus autilus and plants indicating such a temperature as 1s now nfo und alo' nO' the borders of the Medi. terranean. A great . mter~ val of tim: appears to have elapsed between the deposition of the last mentioned (tertiary) strata, and the seconda·ry forma~ tions which constitute the principal portion of the more ele~ vated land in Europe. In these secondary rocks a very dis~ tinct ·assemblage of organized fossils are. entombed, all of unknown species, and many of them refernbl.e to genera, and families now most abundant between the tropics. Among the most remarkable, are many gigantic reptiles, some of them herbivorous, others carnivorous, and far exceeding in size any now known even in the torrid zone. The genera are for the most part extinct, but some of them, as the crocodile and monitor, have still representatives in the warmest parts of the earth. Coral reefs also were evidently numerous in the seas of the same period, and composed of species belonging to genera now characteristic of a tropical climate. The number of immense chambered shells also leads us to infer au elevated temperature ; and the associated fossil plants, although imperfectly known, tend to the same conclusion, the Cycadere con· stituting the most numerous family. But the study of the fossil flora of the coal deposits of still higher antiquity, has yielded the most extraordinary evidence of an extremely hot climate, for it consisted almost exclusively of large vascular cryptogamic plants. We learn, from the labours of M. Ad. Brongniart, that there existed, at that epoch, Equiseta upwards of ten feet high, and from five to six inches in diameter; tree * In the London clay, I believe, no recent species are yet discovered. But of twelve hundred species of shells, collected from the different fresh-water and marine formations of the Paris basin, M. Deshayes isforms me, that there are .som~, but not perhaps exceeding one in a hundrell, which he regards as perfectly 1den~l· cal with living species. Among these are Melanopsis buccinoides, from Epemals, now living in the Grecian archipelago, and Melania inquinata, now found between the tropics in the Phillippine islands. Venus divaricata is not uncommon in the calcaire grossier at Grignon. FOSSIL COAL PLANTS. IOl ferns of from forty to fifty feet in height, and arborescent Lycopodiacere, of from sixty to seventy feet high*. Of the above classes of vegetables, the species are all small at present in cold climates; while in tropical regions, there occur, together with small species, many of a much greater size, but their development at present, even in the hottest parts of the globe, is inferior to that indicated by the petrified forms of the coal formation. An elevated and uniform temperature, and great humidity in the air, are the causes most favourable for the numerical predominance, and the great size of these plants within the torrid zone at present. t If the gigantic size and form of these fossil plants are remarkable, still more so is the extent of their geographical distribution; for impressions of arbore?cent ferns, such as characterize our English carboniferous strata, have been brought from Melville island, in latitude 75° +· The corals and chambered shells, which occur in beds interstratified with the coal (as in mountain limestone), afford also indications of a warm climate,-the gigantic orthocerata of this era being, to recent multilocular she1ls, what the fossil ferns, equiseta, and other plants of the coal strata, are in comparison with plants now growing within the tropics. These shells also, like the vegetable impressions, have been brought from rocks in very high latitudes in North America. * Consid. Generales sur la Nature de la Vegetation, &c. Ann. des Sci. Nat. Nov. 1828. t Humboldt, in speaking of the vegetation of the present era, consillers the laws which govern the distribution of vegetable forms to be sufficiently constant to enable a botanist, who is informed of the number of one class of plants, to conjecture, with tolerable accuracy, the relative number of all others. It is premature, }lerhaps, to apply this law of proportion to t4e fossil botany of strata, between the coal formation and the chalk, as M. Adolphe Brongniart has attempted, as the number of species hitherto procured is so inconsiderable, that the quotient would be materially altered by the addition of one or two species. It may also be objected, that the fossil flora consists of such plants as may accidentally have been floated into seas, lakes, or estuaries, and may often, perhaps always, give a false representation of the numerical relations of families, then living on the land. Yet, after allowing for all liability to error on these grounds, the argument founded on the comparative numbers of the fossil plants of the carboniferous strata is very strong. Martius informs us, that on seeing the tesselated surface of the st~,Jms of arborescent ferns in Brazil, he was reminded of their prototy}Jes, in the impressions which he had seen in the coal-mines of Germany. t Mr. Konig's description of the rocks brought home by Captain Parry, J ourn of Science, vol. xv. p. 20, |