of fire appears to have declined in force, and aqueous agencies are exerting themselves. The earlier portion of this formation is rendered peculiarly interesting by the fact, that during it the most ancient forms of life sprang into existence. It is true that merely a few species of shell-fish, with some corals, inhabited the depths of the ocean, while the dry land still remained untenanted; nevertheless, humble and scanty as they were, we can not fail to look with interest on the earliest types of that existence, which has subsequently reached such perfection in ourselves.
The presence of corals shows, that although the transition seas had lost their high temperature, yet they retained a sufficient degree of heat to encourage the development of animals requiring warmth. These minute animals possess the remarkable property of extracting from the elementary bodies held in solution in the waters, the materials for forming new rocks. To the coral animalcule or polype we owe much of the vast limestone beds which are found in every part of the world, and many a vessel laden with the riches and productions of the earth finds a grave on the sunken reefs that are the fruit of its labors.
As ages elapsed, and the universe became better adapted for the reception of life, the waters swarmed with zoophytes and corals, and in the silurian strata we find organic remains abundant; shell-fish are numerous and distinct in form, and in some instances display a very interesting anatomical construction. As an instance we may mention the Trilobite, an animal of the crustacean order; the front part of its body formed a large crescent-shaped shield, while the hinder portion consisted of a broad triangular tail, composed of segments folding over each other like the tail of a lobster; its most peculiar organ, however, was the eye, which was composed of four hundred minute spherical lenses placed in separate compartments, and so situated, that in the animal's usual place at the bottom of the ocean it could see every thing around. This kind of eye is also common to the existing butterfly and dragon-fly, the former of which has 35,000, and the latter 14,000 lenses.
Continuing to trace the history of this ancient period, we reach what is called among geologists the Old Red Sandstone age. The corals, and the shell-fish, and the crustacea of the former period have passed away, and in their place we find fishes; thus presenting to us the earliest trace of the highest order of the animal kingdom – vertebrata. The plants in this system are few, and it would seem as if the condition of the world was ill-adapted for their growth. Another peculiar characteristic of this era is the state of calm repose in which the ocean appears to have remained; in many rocks the ripple mark left by the tide on the shores of the ancient seas is clearly visible; nevertheless considerable volcanic action must have taken place, if we are to believe geologists, who find themselves unable to account otherwise for the preponderance of mineral matter which seems to have been held in solution by the waters.
We now pass on to the Carboniferous period, and a marked change at once strikes us as having taken place. In the previous era few plants appear to have existed; now they flourished with unrivaled luxuriance. Ferns, cacti, gigantic equisetums, 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 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 store-houses, 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 ferruginous 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 production of the earth to increase the riches, and multiply the comforts, and ameliorate the condition of mankind."
This may justly be 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, solitary 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 Megalichthys, 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; on the contrary, species seem to succeed species abruptly, and at certain definite intervals. A celebrated geologist18 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 mould 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 stone 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 size 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 vertebræ to those of fishes. This saurian Dr. Buckland describes as something similar