The whole of these rocks, from the surface to the soft Lower Ludlow shale here described would better represent the series of connecting links conducting us down from the Crawstone Crust at the Black Rock Quarry than any shaft section we could find described, and the whole may properly be classified as Millstone grit, which is known to attain a thickness of 80 feet in this locality, and to increase to 120 and 150 at a short distance from here, whilst in Derbyshire it thickens to 350 feet, and elsewhere to a maximum of 1,000 feet, and includes, as here, shales and thin coals. Colliers recognise the ironstone which crops out here as the Poor Robin of the Dawley Deep field pit, which occurs 60 feet below the Little Flint Coal; which affords another key to the series of measures which underlie the same coal at the Black Rock Quarry. The Poor Robin however here described must not be confounded with the one of the same name in south Staffordshire, which occurs higher up in the series.
We have given a few, and those the lower coals only, such as are found in the vicinity of Coalbrookdale; it would require more space than we can devote to it to enter upon a description of the measures occurring higher up in the series, in what is called the Coalbrookdale Coalfield. The ideal representation given of coal producing plants at the head of this article and in subsequent pages, and the one given p. 213, will convey a tolerable idea of the surface as it occurs to the minds of geologists during successive periods of the coal formation, and upon which we purpose offering some remarks, condensed and as brief as is consistent with a due explanation of the circumstances. We have already spoken of the oil which exudes from the rock described. It is the same which oozed from a similar rock at the “Tar Tunnel” at Coalport, at the rate, it is said, of 1,000 barrels per week. We extract from it naptha, rectified naptha, gas to illumine our houses, and those magnificent colours derived from the sun’s rays when the earth was young and green, mauve, magenta and a hundred medium tints.
Coal itself rarely contains well preserved specimens of plants, but Sporangia (Flemingites gracilis) may be found in the Lancashire Ladies’, the Flint coal, and most if not all others, the tough little seed cases having resisted the effects of fermentation and crystallization, which destroyed the cellular tissues of plants, but which may sometimes be seen in a carbonised state. If the reader will be at the trouble to split open a piece of coal where he finds brown streaks at the edge, he may detect with the naked eye thousands of little discs clustered and heaped together so thick as to constitute one third at least of the coal; and if he applies a lens he will find some open, with bright amber coloured matter inside; and others closed and imbricated. We have found them in all the coals we have yet examined. Let any one doubtful of the vegetable origin of coal take a bass burnt white from the grate, tap it on the edge, and he will find between the laminated plates numerous impressions of plants. Lindley and Hutton, from experiments instituted by them, state that plants such as are represented on pages 305 and 313, were peculiarly adapted for preservation under water.
Many hundreds of species of plants have been made out, two thirds being ferns. Very beautiful and clear impressions of the accompanying one, Alethopteris lonchitica, or true fern, are obtained, the finest impressions being generally in the Ballstone. It was in fact the great age of ferns: as many as 250 having been described, according to form, structure, &c. Thus, we get:—Asterophyllites (star leaf fern), Cyclopteris (round fern) chiefly in the Ballstone, Caulopteris (star fern); Sphenopteris (wedge shape fern); also Newropteris, or nerved winged fern, which are given on the two following pages:—
Many bear strong resemblances at a first glance to others cultivated in our greenhouses, or growing wild in their favourite habitats, and some approximate so closely to living forms as to make it a question whether they should be classified with different genera or not. The number is remarkable, considering that not more than sixty distinct species are at present indigenous to Europe. The tree ferns of modern horticultural gardens, with their scar-marked trunks and branching fronds, like those from the Mauritius, Brazil, and the Isle of Bourbon, convey tolerable ideas of those of the coal-measure period. We have already spoken of the mare’s-tail of antediluvian times; it is seen in the full page representation, with its glorious head towering high, and the young shoots peering above the slime. Deep in the forest is a species sending forth silky streamers; and prostrate is a species of Lepidodendron, or scaly tree, with branches feathered to the end and bearing cones as scaly as the tree. Others also shoot out their leaves; the Ulodendron staggers beneath its large arm-bearing cones, whilst the seal-impressioned Sigillaria towers high and overtops the whole with its noble crown of foliage. The roots of the latter lie by thousands on our coal-banks, showing distinctly whence the smaller fibres started; some are still connected, being protected by a matrix that formed the sandy soil in which they grew. Water-reeds and forest trees, green parasitic plants, ribbed and jointed, sending forth long-entangling feelers, must have woven a mantle of vegetation rank, matted, and dense in shadow, over the marshy platform where reptiles lurked at intervals. Of the inhabitants of those newly-formed forest lands, scorpions, beetles, flies, and a few reptiles, are all that have yet been found among the relics of the Shropshire coalfields. Saving the buzzing of a beetle and the whirring flight of a scorpion, the shaking of great fronds and fruits, and the sighings of the forest as hot breezes shook the giant pines and rung the pendant catkins, or the sudden splash of some strange fish seizing upon its prey, no sounds were heard. Unlike our woods and copses, all was silence: no songs of birds, no carolling of larks, no warbling of thrushes, no lowing of cattle, no bleating of sheep, and no human voice to break the stillness.
