XI. ness, and disappearing in the twinkling of an eye. Thus BOOK the bolides, or atmospheric stones, should be concretions formed by the elementary gases, and perhaps by an effect of electricity; but they may also be regarded as so many satellites, or diminutive moons, which, revolving round our planet, terminate their course by uniting themselves to it, when causes that are unknown, but easy to be conceived, have deprived them of a part of their centrifugal force. Has Dr. Franklin been wrong in thinking, “that there may have been a time when it rained stones as it now does water ?” It now remains for us only to take a rapid survey of the substances which are foreign to the mineral kingdom, and which are found inserted amongst those that form the solid crust of the globe. These substances deserve a particular section to be appropriated to them. General view. Fossil re mains. Petrifactions. BOOK XII. Continuation of the Theory of Geography. Of the Fossil remains of Organic Bodies, Vegetable and Animal. THE remains of organic beings buried in the earth may be viewed as so many geological medals, but medals without a date. The difference of age and of origin between the secondary and the ternary rocks would be easily ascertained, if we could precisely and completely class the remains of organic bodies, each according to the earth or rock in which it is found; but this arduous undertaking, scarcely ever conceived by systematic geologists, has only of late become the object of researches that deserve to be called scientific.* Organic fossil bodies may be distributed into three classes; remains which have preserved their natural state, at least in part; petrified substances, and impressions. The first class consists principally of bones, and even whole skeletons, which, after having been deprived of the skin and flesh that covered them, remain buried in the earth, or concealed in deep caverns. Sometimes they are calcined totally or in part, without having lost their configuration; sometimes they retain not only their texture, but even a certain portion of skin and flesh; we occasionally find them incrusted with a calcareous covering. Petrifactions, taking this term in the ordinary sense, *G. Cuvier, Extrait d'un ouvrage sur les espèces des quadrupèdes dont on a trouvé les ossemens dans l'intérieur de la terre. Paris, an ix. Et ses Mémoires dans les Annales du Muséum d'Histoire Naturelle. Lamarck, Mémoires sur les coquillages fossiles des environs de Paris. Annal. du Muséum. Blumenbach, Specimen Archæologiæ Telluris; See Gazette des Sciences de Gottingue, No. 199. XII. comprehend all the stony substances which have the figure BOOK of an organic body. There have been instances where a liquid impregnated with stony particles has flowed into a cavity formed by an organic body which had disappeared. In that case, the stony mass has flowed into the empty cavity, and assumed the exterior form of the organic body which was there before. If this body was, for example, a branch or trunk of a tree, the stone will have knots and wrinkles on its exterior; but in the interior it will exhibit all the characters of real stone. It will only be, according to Haüy, "the statue of the substance which it has replaced." wood. While the process of decomposition is going on gradually and obviously in a vegetable or animal substance, it is sometimes likewise surrounded and pressed on by a stony juice. As each organic particle dissolves and disappears, a stony particle replaces it. Thus, particle after particle, the stony substance gradually occupies the spaces left vacant by the progressive decay of the vegetable or animal parts; and, by being moulded in these cavities, it copies, feature for feature, the contexture of the organic body. This is the way in which it is usual to explain the formation of petrified Petrified wood, an imitation of the real wood so complete, that upon cutting it transversely, we distinguish the appearance of concentric rings, which in the living tree arise from its annual growth. Sometimes it is even in a state from which we can ascertain by the lineaments of the texture the species to which the tree belonged.* Mineralized bodies, and those which have been changed Mineraliz into bitumen or into coal, may be referred to the same system of formation. Thus, the turquoises for example, are the jaw teeth of some large sea animal; a metallic substance which has penetrated them, has been gradually substituted for the softer parts of the bone. Delamétherie justly observes, that the siliceous matter * Mongez le Jeune, Journal de Physique, 1731, p. 255, et suiv. (Comp. Daubenton, dans les Leçons de l'Ecole Normale, tome iii. p. 393, et suiv.) ed bodies. BOOK Impressions. Petrified so abundant in many organic bodies, lies crystallized in the bosom of the earth, and produced a great part of the stony substance which constitutes petrifactions-for these being often of a siliceous nature, although found in the midst of clay, whence then could have come this siliceous liquid, if not from the petrified body itself? Impressions are found between the lamina of certain argillaceous schists; they are the relievos or moulds representing skeletons of animals, particularly fishes, leaves, reeds, entire plants, principally of the fern kind. These last impressions have this peculiarity, that if one of the leaves presents a concave print of the face of the leaf opposite to that which bears the fructifications, (as generally happens,) the other lamina will present, not the hollow impression of the face of fructification, but the relievo of the same face, which is concave upon the other leaf. To all appearance, as Brugnieres explains it,* the fern placed upon soft clay has been covered over again with a new deposit. Afterwards, this plant reduced into a carbonaceous substance, or penetrated by the minute particles of the schistous deposit, becomes incorporated and identified with it; and, as the surface of the fructifications is unequal, that opposite being more smooth, it is natural to imagine that there has been less cohesion between the clay and this smoother face. Hence the reason why this latter face generally presents itself, when the leaves of the clayey schists are separated. We shall now consider successively the different classes of fossil remains. The petrifactions of vegetables seem to belong to the quartzeous, aluminous, and magnesian schists, rather than to the calcareous rocks. The petrifying substance is most frequently of quartzvegetables. agate, onyx, or jasper, it is not uncommon to meet with petrifications which have been formed by pyrites.‡ We * Journal d'Histoire Naturelle, No. 4. p. 125. et suiv. † D'Argenville, Oryctologie, p. 355, tab. xx. Stoppen, Récréations Physiques, i. 702. Schulzen, sur les Bois pétrifiés. Dresde, 1754. Henckel, Pyritol. 224, 227, (en Latin.) Denso, Biblioth. Physique, i. 159. XII. have seen a piece petrified by pyrites on the one side, and BOOK by agates on the other.* Petrified vegetables in lime, in gypsum, and even in clay, appear to be less frequent. Fossil ears of corn, impregnated with silver, with copper, and with other metallic substances, have been found in Switzerland, and near Frankenberg, in Hesse. Sometimes only the exterior forms of the vegetables are perceptible; at other times, the different rings of the wood and tissue of the bark are to be distinguished. The "osteocolles," or calcareous tubes, appear to be incrustations formed around a vegetable root, which, deprived of its nourishing juices, has at last completely disappeared. Petrified fruits are sometimes spoken of, but they are very rare. They have been found on heights, where now they do not grow. A trunk of a petrified tree has been met with upon Mount Stella, in the country of the Grisons, at 4000 feet above the level where the last shrubs grow. Entire beds of petrified wood exist at the elevation of 1500 feet above the sea, near the town of Munda, in Spain.§ getables. The impressions of vegetables are almost exclusively Impresfound in the marly and argillaceous schists. Those of sins of veleaves and branches are common. Some have been met with, which present to us the most delicate traces of the structure of flowers, amongst others, the aster alpinus, near Ihlefeld, in the county of Hohenstein. Like petrifactions they sometimes represent indigenous plants, or such as are natives of neighbouring countries; but those that are found in Europe oftener belong to the tropical climates of India and America. -Bernard de Jussieu had remarked, about a century ago, These vethat the greater part of the fossil plants which are found getables in the bituminous schists of Saint Chaumond, near Lyons, Bergmann, Géographie Physique, i. 307. † Scheuchzer, Oryctograph. Helvet. 209. Lehmann, Mémoires Physicochimiques, (en All.) Mémoires de l'Academie des Sciences de Paris, an 1710. Hollmann, Philosoph. Transact. 1760, p. 506, 899. || Bergmann, Géog. Phys. i. 303. are exotics |