450 CHAPTER XVIII. Proofs of Design in the Structure of Fossil SECTION I. GENERAL HISTORY OF FOSSIL VEGETABLES. THE history of Fossil Vegetables has a twofold claim upon our consideration, in relation to the object of our present enquiry. The first regards the influence exerted on the actual condition of Mankind, by the fossil carbonaceous remains of Plants, which clothed the former surface of the Earth, and has been briefly considered in a former chapter; (Chap. VII. P. 63.) the second directs our attention to the history and structure of the ancient members of the vegetable kingdom. It appears that nearly at the same points in the progress of stratification, where the most striking changes take place in the remains of Animal life, there are found also concurrent changes in the character of fossil Vegetables. A large and new field of investigation is thus laid open to our enquiry, wherein we may compare the laws which regulated the varying sys tems of vegetation, on the earlier surfaces of our earth, with those which actually prevail. Should it result from this enquiry, that the families which make up our fossil Flora were formed on principles, either identical with those that regulate the development of existing plants, or so closely allied to them, as to form connected parts of one and the same great system of laws, for the universal regulation of organic life, we shall add another link to the chain of arguments which we extract from the interior of the Earth, in proof of the Unity of the Intelligence and of the Power, which have presided over the entire construction of the material world. We have seen that the first remains of Animal life yet noticed are marine, and as the existence of any kind of animals implies the prior, or at least the contemporaneous existence of Vegetables, to afford them sustenance, the presence of sea weeds in strata coeval with these most ancient animals, and their continuance onwards throughout all formations of marine origin, is a matter of a priori probability, which has been confirmed by the results of actual observation. M. Adolphe Brongniart, in his admirable History of Fossil Vegetables,* has shewn, that the existing submarine vegetation seems to admit of three great divisions which characterize, to a certain degree, the Plants of the frigid, temperate, and torrid zones; and * Histoire des Végétaux Fossiles, 4to. Paris, 1828. that an analogous distribution of the fossil submerged Algæ appears to have placed in the lowest and most ancient formations, genera allied to those which now grow in regions of the greatest heat, whilst the forms of marine vegetation that succeed each other in the Secondary and Tertiary periods, seem to approximate nearer to those of our present climate, as they are respectively enclosed in strata of more recent formation.* If we take a general review of the remains of terrestrial Vegetables, that are distributed through the three great periods of geological history, we find a similar division of them into groups, each respectively indicating the same successive dimi * See Ad. Brongniart's Hist. de Vég. Foss. 1 Liv. p. 47.Dr. Harlan in the Journal of the Academy of Nat. Sc. of Philadelphia, 1831, and Mr. R. C. Taylor in Loudon's Mag. Nat. Hist. Jan. 1834, have published accounts of numerous deposits of fucoids, as occurring in repeated thin layers among the Transition strata of N. America, and extending over a long tract on the E. flank of the Alleghany chain. The most abundant of these is the Fucoides Alleghaniensis of Dr. Harlan. Mr. R. C. Taylor has found extensive deposits of fossil Fuci in the Grauwacke of central Pennsylvania; in one place seven courses of Plants are laid bare in the thickness of four feet, in another, one hundred courses within a thickness of twenty feet. (Jameson's Journal, July, 1835, p. 185.) I have also seen Fucoids in great abundance in the Grauwacke-slate of the Maritime Alps, in many parts of the new road between Nice and Genoa. I once found small Fucoids dispersed abundantly through shale of the Lias formation, from a well at Cheltenham. The Fucoides granulatus occurs in Lias at Lyme Regis, and at Boll in Wurtemberg; and F. Targionii in the Upper Green-sand near Bignor in Sussex. nutions of Temperature upon the Land, which have been inferred from the remains of the vegetation of the Sea. Thus, in strata of the Transition series, we have an association of a few existing families of Endogenous Plants,* chiefly Ferns and Equisetacea, with extinct families both Endogenous and Exogenous, which some modern botanists have considered to indicate a Climate hotter than that of the Tropics of the present day. In the Secondary formations, the species of these most early families become much less numerous, and many of their genera, and even of the families themselves entirely cease; and a large increase takes place in two families, that comprehend many existing forms of vegetables, and are rare in the Coal formation, viz. Cycadeæ and Coniferæ. The united characters of the groups associated in this series, indicate a Climate, whose temperature was nearly similar to that which prevails within the present Tropics. In the Tertiary deposits, the greater number of the families of the first series, and many of those of the second, disappear; and a more complicated dicotyledonous ↑ Vegetation takes place of * • Endogenous Plants are those, the growth of whose stems takes place by addition from within. Exogenous are those in which the growth takes place by addition from without. + Monocotyledonous Plants are those, the embryo of whose seed is made up of one cotyledon or lobe, like the seed of a Lily or an Onion. Dicotyledonous Plants are those, the embryo of the simpler forms which predominated through the two preceding periods. Smaller Equisetaceæ also succeed to the gigantic Calamites; Ferns are reduced in size and number to the scanty proportions they bear on the southern verge of our temperate climates; the presence of Palms attests the absence of any severe degree of cold, and the general character marks a Climate nearly approaching to that of the Mediterranean. We owe to the labours of Schlotheim, Sternberg and Ad. Brongniart the foundation of such a systematic arrangement of fossil plants, as enables us to enter, by means of the analogies of recent plants, into the difficult question of the Ancient Vegetation of the Earth, during those periods when the strata were under the process of formation. Few persons are aware of the nature of the evidence, upon which we have at length arrived at a certain and satisfactory conclusion, respecting the long disputed question as to the vegetable origin of Coal. It is not unfrequent to find among whose seed is made up of two lobes, as in the Bean and Coffee seed. The stems of Monocotyledonous Plants are all Endogenous, i. e. increase from within by the addition of bundles of vessels set in cellular substance, and enlarge their bulk by addition from the centre outwards, e. g. Palms, Canes, and Liliaceous plants. The steins of Dicotyledonous Plants are all Exogenous, i. e. increase externally by the addition of concentric layers from without; these form the rings, which mark the amount of annual growth in the Oak and other forest trees in our climate. |