A Pictorial Atlas of Fossil Remains, consisting of coloured illustrations selected from Parkinson's "Organic remains of a former world," and Artis's "Antediluvian phytology."

by Gideon Algernon Mantell

[104] See Medals of Creation, vol. ii. chap. i.; and Thoughts on a Pebble, pp. 20, 69.

[VII.] Coal.—The numerous fossil plants from the carboniferous strata that are figured in this work, render it necessary to put the general reader in possession of a concise view of the nature and mode of formation of those ancient accumulations of vegetable matter, which now constitute the beds of mineral fuel termed coal.

Although at the present time no one at all conversant with geology doubts the vegetable origin of Coal, the period is not distant when many eminent philosophers were sceptical on this point; and the truth in this, as in most other questions In natural philosophy, was established with difficulty. The experiments and observations of the late Dr. Macculloch mainly contributed to solve the problem as to the vegetable origin of this substance; and that eminent geologist successfully traced the transition of vegetable matter from peat-wood, brown coal, lignite, and jet, to coal, anthracite, graphite, and plumbago. Nor must the important labours of Mr. Parkinson in this field of research be forgotten. The first volume of the "Organic Remains of a former World," which treats of vegetable fossils, contains much original and valuable information on the transmutation of vegetable matter, by bituminous fermentation, into the various mineral substances in which its original nature and structure are altogether changed and obliterated; and that work may still be consulted with advantage by the student.

But though the vegetable origin of all coal will not admit of question, yet evidence of the original structure of the plants or trees whence it was derived is not always attainable. The most perfect coal seems to have undergone a complete liquefaction, and if any portions of the vegetable tissue remain, they appear as if imbedded in a pure bituminous mass. The slaty coal generally preserves traces of cellular or vascular tissue, and the spiral vessels and dotted cells of coniferous trees may often be detected by the microscope. In many instances the cells are filled with an amber-coloured resinous substance; in others the organization is so well preserved, that on the surface of a block of coal cracked by heat, the vascular tissue, and the dotted glands, may be observed. Some beds of coal appear to be wholly composed of minute leaves or disintegrated foliage; for if a mass recently extracted from the mine be split asunder, the exposed surfaces are found covered with delicate laminæ of carbonized leaves and fibres matted together; and flake after flake may be peeled off through a thickness of many inches, and the same structure be apparent. Rarely are any large trunks or branches observable in the beds of coal; but the general appearance of the carboniferous mass is that of an immense deposit of delicate foliage shed and accumulated in a forest, and consolidated by great pressure while undergoing that peculiar process by which vegetable matter is converted into carbon.

The essential conditions for the transmutation of vegetable substances into coal, appear to be the imbedding of large quantities of recent vegetables beneath deposits which shall exclude the air, and prevent the escape of the gaseous elements when released by decomposition from their organic combination; hence, according as these conditions have been more or less perfectly fulfilled, coal, jet, lignite, brown-coal, peat-wood, &c. will be the result.

[VIII.] Fossil Corals.—The real nature even of recent Corals is in general so imperfectly understood by the intelligent reader who has not paid especial attention to the department of natural history which treats of the class of animated nature termed Zoophytes, that in describing the Fossil Corals In my Wonders of Geology, I felt it necessary to devote one Lecture to the consideration of Corals and Crinoidea, in order to afford a popular exposition of the structure and economy of these highly Interesting tribes of animal existence.[105]

[105] See Wonders of Geology, vol. ii. Lect. vi. p. 588.

A very prevalent error regarding their nature Is, that the beautiful stony substances generally called corals, are fabricated by the animalcules which inhabit the cells when living, in the same manner as is the honeycomb of the bee and wasp. This opinion is utterly erroneous: the coral is secreted by the integuments or membranes with which when recent it was invested and permeated; in like manner as are the bones of the skeleton in the higher orders of animals by the tissues designed for that especial purpose, and wholly without the cognisance or control of the creature of which they constitute the internal support.

A general idea of the nature of the compound coral-zoophytes may be obtained by the examination of the common Flustra or Sea-mat. This form of polyparia, when taken out of the water, appears to the naked eye like a patch of fine varnished net-work, adhering to a piece of sea-weed or stone; when viewed with a magnifying lens of moderate power, the surface is found beset with pores regularly disposed: and if the Flustra be examined while immersed in sea-water, its surface is seen to be invested by a gelatinous substance, and every pore is the aperture of a cell, whence issues a tube fringed at the extremity with long tentacula or feelers. These expand, then suddenly contract, withdraw into the cell, and again issue forth: the whole surface of the Flustra being studded with the hydra-like animalcules; each enjoying a distinct existence, the entire group being united by one common integument or calcareous frame-work. When the Flustra is exposed to the air, the polypes soon perish, the animal matter rapidly decomposes, and the calcareous lace-like skeleton alone remains. In the larger and more compact corals the phenomena are similar, differing only in degree. In a fossil state, the durable remains of the corals consist for the most part of the calcareous frame-work (or polyparium, as it is termed), which often possesses a crystalline structure; and in some instances is completely transmuted into silex, as in specimens from Antigua, the Falls of the Ohio, and from Tisbury in Wiltshire. (See [Plate XXXVIII.] figs. 12, 13.)