« AnteriorContinuar »
dendra, or extinct Coniferae. (See Lindley and Hutton, Foss. Flora, vol. ii. p. 93.)
The recent discoveries of Lindley and Hutton have thrown much light upon this very extraordinary family of extinct fossil plants. Our figure, PI. 56, Fig. 8, copied from their engraving of Stigmaria ficoides, (Foss. Flora, PI. 31, Fig. 1) represents one of the best known examples of the genus.f
The centre of the plant presents a dome-shaped trunk or stem, three or four feet in diameter, the substance of which was probably yielding and fleshy; both its surfaces were slightly corrugated, and covered with indistinct circular spots. (PI. 56, Figs. 8. 9.)
From the margin of this dome there proceed many horizontal branches, varying in number in different individuals from nine to fifteen; some of these branches become forked at unequal distances from the dome; they are all broken oftehort, the longest yet found attached to the stem, was four feet and a half In ionSth The extent of these branches, when outstreched and perfect, was proWMy from twer>*r to thirty feet.J The surface of each branch is covered with
spirally disposed tubercles, resembling the papillae at the base of the spines of Echini. From each tubercle there proceeded a cylindrical and probably succulent leaf; these extended to the length of several feet from all sides of the branches. (PL 56, Figs. 10. 11.) The leaves, usually, in a compressed state, are found penetrating in all directions into the sand-stone or shale which forms the surrounding matrix; they have been traced to the length of three feet, and have been said to be much longer.*
In many of the strata that accompany the coal, fragments of these plants occur in vast abundance; they have been long noticed in the sand-stone called Gannister and Crowstone, in the Yorkshire and Derbyshire coal fields, and have been incorrectly considered to be fragments of the stems of Cacti.
The discovery of the dome-shaped centres above described, and the length and forms of the leaves and branches render it highly probable that the Stigmatiae were aquatic plants, trailing in swamps, or floating in still and shallow lakes, like the modern Stratiotes and Isoetes. From such situations they may have been drifted by the same inundations, that transported the Ferns and other land vegetables, with which they are associated in the coal formation. The form of the trunk and branches shows that they could not have risen upwards into the air; they must therefore either have trailed on the ground, or have floated in water .J The Stigmaria was probably dicotyledonous, and in its internal structure seems to have borne some analogies to that of the Euphorbiaceae.
sion there is found a loose internal eccentric axis, or woody core (PI. 56. Fig. 10. a.) surrounded with vascular fasciculi that communicated with the external tubercles, and resembled the internal axis within the stems of certain species of Cactus.
* All these are conditions, which a Plant habitually floating with the leaves distended in every direction, would not cease to maintain, when drifted to the bottom of an Estuary, and there gradually surrounded by sediments of mad and silt.
-f The place and form of the leaves, supposing them to have grown on all sides of branches suspended horizontally in water, would have been but little changed by being drifted into, and sinking to the bottom of, an estuary or sea, and there becoming surrounded by sediments of mud or sand. This hypothesis seems supported by the observations made at Jarrow, that the extremities of the branches descend from the dome towards the adjacent bed of coal.
Besides these Genera which have been enumerated, there are many others whose nature is still more obscure, and of which no traces have been found among existing vegetables, nor in any strata more recent than the Carboniferous series.* Many years must elapse before the character of these various remains of the primeval vegetation of the Globe can be fully understood. The plants which have contributed most largely to the highly-interesting and important formation of Coal, are referable principally to the Genera whose history we have attempted briefly to elucidate: viz. Calamites, Ferns, Lycopodiaceae, Sigillaria?, and Stigmariae. These materials have been collected chiefly from the carboniferous strata of Europe. The same kind of fossil plants are found in the coal mines of N. America, and we have reason to believe that similar remains occur in Coal formations of the same Epoch, under very different Latitudes, and in very distant quarters of the Globe, e. g. in India, and New Holland, in Melville Island, and Baffin's Bay.
The most striking conclusions to which the present state of our knowledge has led, respecting the vegetables which gave origin to coal are, 1st, that a large proportion of these plants were vascular Cryptogamiae, and especially Ferns; 2dly, that among these Cryptogamic plants, the Equisetaceae attained a gigantic size; 3dly, that Dicotyledonous plants, which compose nearly two-thirds of living Vegetables, formed but a small proportion of the Flora of these early periods.* 4thly, that although many extinct genera, and certain families have no living representatives, and even ceased to exist after the deposition of the Coal formation, yet are they connected with modern vegetables by common principles of structure, and by details of organization, which show them all to be parts of One grand, and consistent, and harmonious Design.
* Some of the most abundant of these have been classed under the names of Asterophyllites, (see PI. 1, Figs. 4. 5.) from the stellated disposition of the leaves around the branches.
* The value to be attached to numerical proportions of fossil Plants, in estimating the entire condition of the Flora of these early periods, has been diminished by the result of a recent interesting experiment made by Prof. Lindley, on the durability of Plants immersed in water. (See Fossil Flora No. xvii. vol. iii. p. 4.) Having immersed in a tank of fresh-water, during more than two years, 177 species of plants, including representatives of all those which are either constantly present in the coal measures or universally absent, he found:
1. That the leaves and bark of most dicotyledonous Plants are wholly decomposed in two years, and that of those which do resist it, the greater part are Coniferat and Cycadea.
2. That Monocotyledons are more capable of resisting the action of water, particularly Palms and Scitamineous Plants; but that Grasses and Sedges perish.
3. That Fungi, Mosses, and all the lowest forms of Vegetation disappear.
4. That Ferns have a great Power of resisting water if gathered in a green state, not one of those submitted to the experiment having disappeared, but that their fructification perished.
Although the results of this experiment in some degree invalidate the certainty of our knowledge of the entire Flora of each of the consecutive Periods of Geological History, it does not affect our information as to the number of the enduring Plants which have contributed to make up the Coal formation; nor as to the varying proportions, and changes in the species of Ferns and other plants, in the successive systems of vegetation that have clothed our globe.
It may be farther noticed, that as both trunks and leaves of Angiospermous dicotyledonous Plants have been preserved abundantly in the Tertiary formations, there appears to bo no reason why, if Plants of this Tribe had existed during the Secondary and Transition Periods, they should not also occasionally have escaped destruction in the sedimentary deposites of these earlier epochs.
In Loudon's Mag. Nat. Hist. Jan, 1834, p. 34, is an account of some interesting experiments by Mr. Lukis, on successive changes in the form of the cortical and internal parts of the stems of succulent plants, (e. g. Sempervivum arboreum) during various stages of decay, which may illustrate analogous appearances in many fossil plants of the coal formation.
VOL. I. 31
We may end our account of the Plants to which we have traced the origin of Coal, with a summary view of the various Natural changes, and processes in Art and Industry, through which we can follow the progress of this curious and most important vegetable production.
Few persons are aware of the remote and wonderful Events in the economy of our Planet, and of the complicated applications of human Industry'and Science, which are involved in the production of the Coal that supplies with fuel the Metropolis of England. The most early stage to which we can carry back its origin, was among the swamps and forests of the primeval earth, where it flourished in the form of gigantic Calamites, and stately Lepidodendra, and Sigillariae. From their native bed, these plants were torn away, by the storms and inundations of a hot and humid climate, and transported in some adjacent Lake, or Estuary, or Sea. Here they floated on the waters, until they sank saturated to the bottom, and being buried in the detritus of adjacent lands, became transferred to a new estate among the members of the mineral kingdom. A long interment followed, during which a course of Chemical changes, and new combinations of their vegetable elements, have converted them to the mineral condition of Coal. By the elevating force of subterranean Fires, these beds of Coal have been uplifted from beneath the waters, to a new position in the hills and mountains, where they are accessible to'the industry of man. From this fourth stage in its adventures, our Coal has again been moved by the labours of the miner, assisted by the Arts and Sciences, that have co-operated to produce the Steam Engine and the Safety Lamp. Returned once more to the