« AnteriorContinuar »
and many plants of which there are no existing types, grew, and lived, and died in vast impenetrable forests; while the bulrush and the cane, or the genera nearly allied to them, occupied the swamps and lowlands. This is the period when the great coal beds and strata of ironstone were deposited, which supply us with fuel for our fires, and materials for our machinery. The interminable forests that grew and died in the lapse of centuries, were gradually borne down by the rivers and torrents to the ocean, at whose bottom they ultimately found a resting-place. A considerable portion of the land, also, seems to have been slowly submerged, as in some cases fossil trees and plants are found in an upright position, as they originally grew.
"There is no period in geological history so justly deserving of examination as this. To the coal beds then deposited, Great Britain in a great measure owes national and mercantile greatness. Dr. Buckland, in speaking of this remote age, remarks in his Bridgewater Treatise, that 'the important uses of coal and iron in administering to the supply of our daily wants, give to every individual among us, in almost every moment of our lives, a personal concern, of which but few are conscious, in the geological events of these very distant eras. We are all brought into immediate connection with the vegetation that clothed the ancient earth, before one-half of its actual surface had yet been formed. The trees of the primeval forests have not like modern trees undergone decay, yielding back their elements to the soil and atmosphere by which they have been nourished; but treasured up in subterranean storehouses, have been transformed into enduring beds of coal, which in these latter ages have been to man the sources of heat and light, and wealth. My fire now burns with fuel, and my lamp is shining with the light of gas derived from coal that has been buried for countless ages in the deep and dark recesses of the earth. We prepare our food and maintain our forges and furnaces, and the power of our steam engines, with the remains of plants of ancient forms and extinct species, which were swept from the earth ere the formation of the transition strata was completed. Our instruments of cutlery, the tools of our mechanics, and the countless machines which we construct by the infinitely varied applications of iron, are derived from ore, for the most part coeval with, or more ancient than the fuel, by the aid of which we reduce it to its metallic state, and apply it to innumerable uses in the economy of human life. Thus, from the wreck of forests that waved upon the surface of the primeval lands, and from feruginous mud that was lodged at the bottom of the primeval waters, we derive our chief supplies of coal and iron, those two fundamental elements of art and industry, which contribute more than any other mineral productions of the earth to increase the riches, and multiply the comforts, and ameliorr ate the condition of mankind.'
"This may be justly styled the golden age of the pre-adamite world ; the globe having now cooled to a sufficient temperature to promote the growth of plants without being injurious to them, is for the first time clothed in all the rich verdure of a tropical climate. Doubtless the earth would have presented a lovely aspect, had it been possible to have beheld it—the mighty forests, unawakened by a sound save that of the sighing of the wind; the silent seas, in which the new-born denizens of the deep roamed at will; the vast inland lakes, for ages unruffled'but by the fitful breeze—all present to the mind's eye a picture of surpassing grandeur. The creatures that existed, though differing from those of the previous age, were still confined to the waters; as yet the dry land remained untenanted. The fishes give evidence of a higher organization, and many of them appear to have been of gigantic dimensions. Some teeth which have been found of one kind, the Megalichtys, equal In size those of the largest living crocodiles.
"There is one peculiarity respecting fossil fishes, which is worthy of remark. It is that, in the lapse of time from one era to another, their character does not change insensibly, as in the case of many zoophytes and testacea species, on the contrary, abruptly and at certain definite intervals. A celebrated geologist has observed, that not a single species of fossil fish has yet been found that is common to any two great geological formations, or that is living in our own seas.
"Continuing our investigation, we next find the fruitful coal era passing away; scarcely a trace of vegetation remains ; a few species of zoophytes, shells, and fishes are to be found, and we observe the impression of footsteps, technically called ichnites, from the Greek ichnon, a footmark. These marks present a highly interesting memento of past ages. Persons living near the sea shore must have frequently observed the distinctness with which the track of birds and other animals is imprinted in the sand. If this sand were to be hardened by remaining exposed to the action of the sun and air, it "would form a perfect mold of the foot ; this is exactly what occurred in these early ages, and the hollow becoming subsequently filled by the deposition of new sediment, the lower retained the impression, while the upper one presented a cast in relief. Many fossil footmarks have been found in the. rocks belonging to this period.
"It is evident from the fact of footmarks being found, that creatures capable of existing on dry land were formed about this time, and we accordingly find the remains of a new order —Reptiles. These animals, which now constitute but a small family among existing quadrupeds, then flourished in great sizo and numbers. Crocodiles and lizards of various forms and gigantic stature, roamed through the earth. Some of the most remarkable are those which belong to the genus Ichthyosaurus, or fish lizard, so called from the resemblance of their vertebras to those of fishes. This saurian, Dr. Buckland describes as something similar in form to the modern porpoise: it had foui broad feet, and a long and powerful tail; its jaws were so prodigious that it could probably expand them to the width of five or six feet, and its powers of destruction must have been enormous. The length of some of these reptiles exceeded thirty feet.
"Another animal which lived at this period was the Plesiosaurus. It lived in shallow seas and estuaries, and would seem from its organs of respiration, to have required frequent supplies of fresh air. Mr. Conybeare describes it as 'swimming upon, or near the surface, arching its long neck like the swan, and occasionally darting down at the fish which happened to float within its reach.'
"This reptile, which was smaller than the Ichthyosaurus, has been found as long as from twelve to fifteen feet. Its appearance and habits differed from the latter materially. The Ichthyosaurus, with its short neck, powerful jaws, and lizardlike body, seems admirably suited to range through the deep waters^ unrivaled in size or strength, and monarch of the then existing world; the Plesiosaurus, smaller in size and inferior in strength, shunned its powerful antagonist, and, lurking in shallows and sheltered bays, remained secure from the assaults of its dangerous foe, its long neck and small head being well adapted to enable it to dart on its prey, as it lay concealed amid the tangled sea-weed.
"This has been called by geologists the 'age of reptiles'; their remains are found in great numbers in the lias, oolite, and wealden strata. These creatures seem to form a connecting link between the fishes of the previous era and the mammalia of the Tertiary age; the Ichthyosaurus differed little from a fish in shape, and its paddles, or feet, are not unlike fins; the Plesiosaurus on the contrary, as its name denotes, partook more of the quadruped form. Dr. Buckland, in describing it, says: 'To the head of a lizard it united the teeth of a crocodile; a neck of enormous length, resembling the body of a serpent; a trunk and tail having the proportions of an ordinary quadruped; the ribs of a camelon, and the paddle of a whale.' Besides these animals we find the Pterodactyle, half bird and half reptile; the Megalosaurus, or gigantic lizard, the Hyheosaurus, or forest lizard; the Geosaurus, or land lizard, and many others, all partaking more or less of affinity to both the piscatory and saurian tribes.
"Passing now to the period when the great chalk rocks which prevail so much in the south-eastern counties of Great Britain were deposited, we find the land in a great many places submerged; the fossil remains are eminently marine in character, and the earth must literally have presented a '. world of waters' to the view. Sponges, corals, star-fish, and marine reptiles inhabited the globe, and plants, chiefly of marine types grew on its surface. Although, however, a great portion of