The formation and structure of existing Coral Reefs being once fairly established, Geologists have little difficulty in ascribing a similar origin to many of the limestone strata that are found in the Crust of the Earth. For though the internal texture has been considerably modified in the long course of ages, by chemical and other influences, nevertheless the stony skeletons of the reef-building Zoophytes can be distinctly recognized in great abundance. Indeed it is not an uncommon thing to meet with limestone rock exhibiting plainly to the eye all the appearance of Coral Reefs lifted up from the bed of the ocean. “The Oolite,” says Doctor Mantell, “abounds in corals, and contains beds of limestone which are merely coral reefs that have undergone no change but that of elevation from the bottom of the deep, and the consolidation of their materials. The Coral-rag of Wilts presents in fact all the characters of modern reefs: the polypifera belong chiefly to the Astræidæ, the genera of which family principally contribute to the formations now going on in the Pacific. Shells, echinoderms, teeth, and bones of fishes, and other marine exuviæ, occupy the interstices between the corals, and the whole is consolidated by sand and gravel, held together in some instances by calcareous, in others by siliceous infiltrations. Those who have visited districts where the Coral-rag forms the immediate subsoil, and is exposed to view in the quarries or in natural sections, must have been struck with the resemblance of these rocks to modern coral banks.”[56]
Even in many of our finest marbles the coral skeletons may be traced distinctly enough, and contribute not a little to that variegated color which is so much admired. Nay, it is recorded by Mr. Parkinson that he discovered in a piece of solid marble, the animal membrane itself by which the lime was originally abstracted from the sea. He immersed the marble in dilute muriatic acid; and he relates with delight how, as the calcareous earth dissolved, and the carbonic acid gas escaped, he observed the animal tissue begin distinctly to appear in the form of light, elastic membranes.[57]
CHAPTER IX.
STRATIFIED ROCKS OF ORGANIC ORIGIN—ILLUSTRATIONS FROM VEGETABLE LIFE.
Origin of coal—Evident traces of plants and trees in coal-mines—Coal made up of the same elements as wood—Beds of coal found resting upon clay in which are preserved the roots of trees—Insensible transition from wood to coal—Forest-covered swamps—Accumulations of drift-wood in lakes and estuaries—Peat bogs—Beds of Lignite—Seams of pure coal with half-carbonized trees, some lying prostrate, some standing erect—Summary of the argument hitherto pursued—Objection to this argument from the Omnipotence of God—Answer to the objection.
As animals, by organic action, extract lime from the waters of the ocean they inhabit, which, being converted in the first instance into minute shells, or stony skeletons, afterward passes into a compact and solid rock, so in like manner do plants and trees extract carbon from the atmosphere in which they vegetate, and convert it into coal. No reasonable doubt can now be entertained that coal derives its existence, almost entirely, from the woody tissue of sunken swamps and forests. Though the nature of the process by which this transformation takes place, is yet but imperfectly understood, and is, indeed, at the present moment a subject of much discussion and controversy, nevertheless the fact that the change has taken place is fully accepted by all as an established truth, and is supported by an accumulation of evidence which it is not easy to resist.
The first circumstance to which we shall call attention, is the wonderful profusion of vegetable life that is always associated with coal. Every one who has descended at any time into a coal mine, or who has examined the specimens usually exhibited in a well-furnished museum, must have been struck by the countless forms of trees and plants, which still remain vividly impressed on this black and unsightly mineral. Dr. Buckland has described this phenomenon with much vigor and beauty in his celebrated Bridgewater Treatise: “The finest example I have ever witnessed is that of the coal mines of Bohemia just mentioned. The most elaborate imitations of living foliage upon the painted ceilings of Italian palaces, bear no comparison with the beauteous profusion of extinct vegetable forms with which the galleries of these instructive coal mines are overhung. The roof is covered as with a canopy of gorgeous tapestry, enriched with festoons of most graceful foliage, flung in wild irregular profusion over every portion of its surface. The effect is heightened by the contrast of the coal-black color of these vegetables with the light ground-work of the rock to which they are attached. The spectator feels himself transported, as if by enchantment, into the forests of another world; he beholds trees of forms and characters now unknown upon the surface of the earth, presented to his senses almost in the beauty and vigor of their primeval life; their scaly stems and bending branches, with their delicate apparatus of foliage, are all spread forth before him, little impaired by the lapse of countless ages, and bearing faithful records of extinct systems of vegetation, which began and terminated in times of which these relics are the infallible historians.”
