tled sandstone formations, we find iron everywhere; but the concentrations even amounting to ten per cent. are but rare exceptions. The presence of the iron would then be scarcely remarked, if the glaring colour of these red and variegated formations did not contrast with the gray and dark rocks of the coal deposits which they cover, and with the white and greenish colours of the thick limestones and clays which are about them.* SECTION III. FOSSIL BOTANY AND GEOLOGICAL DISTRIBUTION OF VEGETABLE REMAINS. IN intimate connection with the matter of the present volume, a knowledge of the forms, the botanical classification, the geological arrangement of the vegetable remains of an ancient world, seems to be almost indispensable. It embraces facts, at least, sufficiently valuable, to ensure for it, as a collateral branch of natural science, a conspicuous section of this book. Independently of its usefulness, there is a never failing interest attached to such an investigation, which enables us to trace the history, as it were, the past condition, the present adaptation of the primeval flora;-that magnificent vegetation which, amidst the mutations of our planet, yet survives for our use; its characters changed, it is true, but only to become more serviceable to man. A happy provision was it that secured for the ultimate advantage of the human race, ages before its appearance upon the globe, the trees of gigantic size, the densely growing shrubs, the most delicate even of the lesser plants-that flora which covered in such profusion the islands and plateaux, and filled the humid valleys of the early world. A happy provision was it, that amidst the early catastrophes of the earth, those convulsions which modified its entire surface, overwhelmed its primeval forests, and buried them beneath enormous accumulations of earthy debris, of sediment and of rocky debaclestill perpetuated and matured during the lapse of countless ages, that primitive vegetation, which, finally, in the form of mineral combustibles, we are now busy in exploring and mining, and appropriating in a thousand ways, and for a thousand purposes. A happy provision was that a beneficent one, surely-which at the moment when man is compelled to level the existing forests, to make room for the progress of agriculture, and the cultivation of the present surface, he finds nigh at hand, yet buried beneath that surface, within the shallow basins and woody islands of the antediluvian world, those inex * Burat.-Géologie appliquée, p. 108. haustible stores of a combustible now rendered infinitely more precious and effective than that existing vegetable fuel, whose destruction is the inevitable consequence of advancing civilization. Respecting the wondrous influence which the employment of mineral combustibles has had, even in our own days, upon the whole world, by the acquisition of new forces; by the extension of mechanical powers, of manufacturing capabilities; by the impulse given to the industrial arts, and the creation of new sources of wealth; by rapid and cheap modes of transportation, and enlarged commercial facilities; above all, by the improved condition of the people, we will not here dilate. Abundant evidence of all these will be found in this volume. FOSSIL BOTANY. Classification of Plants; their families, classes, and orders.-We shall occasionally have to make mention of the varieties of plants which occur in a fossil state, and which, in common with all other organic remains, are characteristic of, or distinguish with remarkable precision, every geological epoch. It may save the reader some trouble in referring to elementary books, if we briefly explain here the mode observed in the classification of this fossil vegetation; of which the true coal formation alone contains about four hundred known species. The system generally adopted by botanists is, that of Jussieu, which is termed the "natural system," in contradistinction to that of Linnæus, which is denominated the "artificial system." Mr. Loudon states that the former method has for its object the arrangement of plants according to their greater or lesser degree of resemblance, both externally and internally. The seed is considered the most important part of the plant; as being destined for its re-production and continuance in the world. The fundamental divisions of this arrangement are, therefore, founded on the characters of seeds. The first grand division is derived from the presence or absence of seed-lobes; the next on the union or division of the seed-lobes in such as have them. Thus we have the three primitive divisions of Cotyledoneæ, Monocotyledoneæ, and Acotyledoneæ.* Every one allows, M. Decandolle observes, that plants which resemble each other by their exterior forms, resemble each other also in their internal structure; their mode of vegetation and their properties. The three primitive divisions are divided by this botanist into eleven classes; and, according to the Jussieuan method, all vegetables are furnished with seeds which arrange themselves under one or other of the following heads. COTYLEDONE.E. Exogenous stems.-Furnished with two or more cotyledons, or • Loudon's Encyclopedia of Gardening, p. 113. seed-lobes; as the bean or the acorn; having a central column or pith, and an external band called the bark, the two being connected by medullary rays; this division being thus subdivided into I. Dicotyledons; II. Monocotyledons; III. Acotyledons. embracing 1255 genera, and 8612 spécies. Plumbaginem, Plantagineæ, Euphorbiacæ, Amentaceæ, &c. Laurinæ, Santalaceæ, Urticeæ, Coniferæ, comprising 172 genera, and 1249 species. Besides 53 genera and 71 species whose orders are not fully determined. Fossil dicotyledonous plants of the coal formation-Until recently the fossilized dicotyledones were supposed to occur not lower than the Tilgate or Upper Oolite beds. The conifere also were considered as not older than the oolite series. But recent investigations, by distinguished naturalists, have shown that these groups formed the greater portion of the coal vegetation. Thus, for instance, some fossil trees, which were discovered rooted in a coal bed in the Lancashire coal-field, were identified by Mr. Bowman as sigillaria,* while at the same time he showed that medullary rays and coniferous structure existed; a fact which M. A. Brongniart, Lindley and Hutton, Humboldt and others have fully corroborated. Hence, it seems that botanists are inclined to withdraw the Sigillaria altogether from the family of tree ferns, with which they have been heretofore classed, and even from the Endogenous class, or Monocotyledones. We are therefore to understand that the Sigillaria is a dicotyledonous and coniferous plant, and that the arborescent ferns, Caulopteræ, belong to the monocotyledonous group. Among the dicotyledonous plants of the coal formation are now arranged 66 66 Sigillaria, 59 species, Asterophillites, II. MONOCOTYLEDONEÆ. Endogenous Stems-furnished with only one cotyledon or seedlobe, [as the lily,] and having neither pith, concentric circles of Proceedings Geological Society, London, vol. iii. p. 270; also Mantell's Medals of Creation, p. 132. woody fibre, nor true bark: distinguishable as follows, in the existing Distribution of Fossil Vegetation.—In a memoir "on the Ancient Flora of the Earth," written some years ago by a contributor to the Edinburgh Philosophical Journal, the author concludes with the following summary: 1st. That among the universally distributed rock formations, [groups] since the first appearance of organic beings, there is not one of them in which the remains of a contemporary land vegetation are not to be observed. 2d. That the different periods of the vegetation of a former age are gradually characterized by the continual entrance of new and always more perfectly organized [?] families of plants; but there is not a complete disappearance of all the species of the preceding periods. 3d. That species of the most perfectly developed class, the dicotyledonous, are first traced in the oldest strata of the secondary formations, while they uninterruptedly increase in the successive formations. To similar views Humboldt opposes some objections, particularly in relation to the theory of the supposed* simplicity of the first forms of organic life, and especially the assumption that vegetable life was awakened sooner than animal life upon the face of the old earth.† With respect to the vegetation of the true coal formation, Sir Alexander Crichton observed, that every coal country in every part of the world, which has been hitherto examined, abounds in the fossil remains of similar or corresponding vegetables. There is no material variety, let the latitude or longitude or elevation be what they may. Recent examinations of the fossil flora of remote coal beds, such as those of Australia, Van Dieman's Land, and Northern India, would seem to point out some exceptions to the rule heretofore adopted, but the evidence is by no means complete that these fields were really of the true coal period. "Every plant in the present Edinburgh Philosophical Journal, January, 1830. † Cosmos, A. Von Humboldt. ་ condition of the globe, independently of its natural dwelling-place, has, as it were, a central spot in which it flourishes best; and considering this spot as the centre of a circle, or rather as a zone, the plant degenerates in proportion as it approaches the limits of this district." The writer goes on to point out a very important circumstance, namely, that there is a difference of mean temperature, at present, of forty-one degrees of heat between the parallels in which coal has been discovered.* Between these, as regards the existing vegetation, the diversity in the genera and species of plants, at present, is very great; so much so, indeed, that there is no resemblance between the floras of the two extreme points. At the time, however, of the true coal formation, it is now admitted that the flora of these two remote parallels was nearly the same, both as to genera and species, and in this respect strongly contrasted with the present condition of things. Fossil Plants of the class Phanerogameæ.-The monocotyledonous family of this class, in the fossil state, commence in the London clay tertiary formation, and, until lately, were thought not to descend lower in the geological series than the oolites, or the Waelden beds, the Portland oolite and the Lias. The cycades [Cycas Zamia] form the connecting link between the ferns and the palms, while, according to the authorities last cited, the sigillaires differ not more from the aborescent ferns [Caulopteris,] yet existing, than the stems of the calamites, the bactris, and other arundinaceous palms,† which order contains, in the recent state, eighteen genera and twenty-nine species. Zamia were very abundant in the oolite period. Eleven species occur in the coal of the Yorkshire oolite alone. Distribution of the Vestiges of Palms in the Geological Formations.-Prof. Unger states, first, That no vestiges of palms have been detected in the earliest rocks which contain the organic remains of maritime and terrestrial plants. Second, That palms bore some small part in the vegetation at the period of the coal formation. He names four species or forms, two of which occur in the coal schist of Swina, Bohemia, one in sandstone of the Ural Mountains, and one from Rajemahl, North India; also two undescribed species from the coal formation of Silesia. Third, The flora of the red sandstone, above the coal series, although it has been very imperfectly preserved, and its scanty remains but little studied, Unger thinks was not materially different from that of the coal formation. But the fossils of this era, which have been referred to palms, he thinks are very doubtful. In the Quadersandstein, Goeppert found some vestiges in Silesia. From the next series, the oolites, the four species of Carpolythes, described by Lindley and Hutton, may be mentioned. Fourth, and finally. In the tertiary, palms reappear, and the This approaches closely to the range we have assigned to the coal formations. American Journal of Science, July, 1846. |