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

Fig. 5.
The under surface of Fig. 3, showing the conical tap-roots of the tree, ¹/₁₂ natural size.

Mr. Brown remarks, that these short thick tap-roots were evidently adapted only to a soft wet soil, such as we may conceive was the nature of the first layer of mud deposited upon a bed of peat which had settled down slightly below the level of the water. He supposes, from the presence of a layer of shale without fossil plants immediately over the coal, that the prostrate stems and leaves which occur in such large quantities in the next superincumbent bed, fell from trees growing on the spot, and were entombed in layers of mud held in suspension in the water, which at short intervals inundated the low marshy ground on which they grew; for had the plants been drifted from a distance, he conceives they would also occur in the first layer of shale, as well as in those higher up.

Fig. 6.
STEM OF A SIGILLARIA BROKEN OFF CLOSE TO THE ROOTS, ¹/₁₂ natural size.

Having thus shown that the Sigillaria alternans was provided with roots adapted for a soft muddy soil, Mr. Brown next describes the specimen represented in Fig. 6, which is the stem of the same species of tree broken off near the roots; the hollow cylinder of bark (a) having been bent down and doubled over by the pressure of the surrounding mud, so as effectually to close up the aperture, leaving only a few irregular cicatrices, of three or four inches in length, converging at the apex; the structure, arrangement, and number of the tap-roots, as well as the horizontal ramifications, are similar to those in Fig. 5. This fossil clearly explains the nature of the "dome-shaped" plant figured in the "Fossil Flora of Great Britain."[148]

[148] The figures 3, 4, 5, 6, and the descriptions, are from the paper of Richard Brown, Esq., published in the Journal of the Geological Society of London, for March, 1849, entitled, "Description of erect Sigillariæ, with conical tap-roots, found in the roof of the Sydney Main Coal, in the Island of Cape Breton."

"The roots of the preceding fossils repeatedly ramify as their distance from the stem increases, and ultimately terminate in broad flattened points. The whole of the spreading roots of these trees (the Sigillariæ) cover only an area of thirty square feet each; whilst those of the Lepidodendron (Fig. 1), whose stem is only two or three inches larger in diameter, covered a space of two hundred square feet. Since it is well known, from numerous examples, that the Lepidodendra were lofty trees, with spreading branches, which therefore required wide bases for support, may we not conclude that Sigillariæ of the species described were, on the contrary, trees of low stature, without heavy branches?"

I cannot quit this subject without again adverting to the remarkable phenomenon mentioned In a previous note, namely, that in the bed of pulverulent earth—the under-clay—on which the coal invariably reposes, the roots (or Stigmariæ) of large trees are generally the only organic remains met with. The constant occurrence of these fossils in the under-clay, and their rarity in the coal and shale, was long ago pointed out by Mr. Martin, Dr. Macculloch, and other geologists; but the importance of the fact was not appreciated till Mr. Logan drew attention to it. In the Welsh coal-field, through a depth of 1,200 feet, there are sixty beds of coal, each of which lies on a stratum of clay abounding in Stigmariæ. In the Appalachian coal formation of the United States, the same phenomena occur.