Coalbrookdale Coalfield
The works of the company in the Dale, at Lightmoor, Horsehay, the Castle, and other parts of Dawley, are so intimately connected and so entirely dependent upon the mineral resources of the district, that some further notice is needed to complete this stretch. We said at the commencement that neither iron nor coal were found here, but in the quotation from the Philosophical Transactions it is stated that Mr. Ford made iron either hard or soft from ore and coal got in the dale; and it may perhaps without being considered a sketch of language be said that the opening into the Lightmoor valley, where coals were undoubtedly worked at an early period, is a northern lip or extension of the Dale itself. Indeed the whole of the rich mineral tract extending from Broseley to the extreme limits of the Lilleshall Company’s works, some seven miles in length, and terminating in a Symon Fault on the south-east of Madeley parish, about four miles in breadth, is universally known as the Coalbrookdale Coalfield; but the Dale proper is a hollow scooped out of soft Silurian shale, which shews itself at the railway station, by the viaduct, on the road to Lightmoor, and in various other places. Here two great faults or rents in the coalfield meet; one coming down from the Dunge at Broseley, and the other from the direction of Lilleshall, causing a difference of level varying from fifty to seven hundred feet. The coal-measures approach the northern extremity of the Dale on three sides, forming a fringe which rises from a few feet above the Dale to three hundred feet above the Severn at Ironbridge, and to over seven hundred feet at the highest points. It was this outside fringe of lower coals which tempted early miners, who by means of levels in the hill sides got their “Smith’s Coal,” leaving others, which they did not then need for house fuel. Interesting instances of the outcrops of these coals are to be seen at the surface on high grounds overlooking the Dale, also on the side of the railway opposite to Black Rock quarry, where an instructive section of the Best, Middle, and Clod Coals are visible, with a slight fault displacing them. They crop out on the side of the Lincoln Hill walks; and on sinking a trial pit at Castle Green near there, many years ago, it was found that the Middle and Clod coals had been removed, and the space filled up with gob. The upper coals here, and also the pennystone, as at the Lodge Pit, remained; but at the latter the clod coal, the best coal for iron-making purposes, was removed, and the space filled up with refuse.
When quarrying stone at the Black Rock, on the right hand side of the tramroad leading to Lightmoor, for the purpose of constructing the viaduct for the Wellington and Severn Junction Railroad, an interesting discovery was made of a number of fossil trees. Some were still clinging to the soil from which they originally derived their nourishment, as here shewn, somewhat imperfectly, by the accompanying engraving. One was twelve feet in circumference at the point at which the roots, which were eight in number, and two feet ten inches in their thickest part, diverged and spread, at a distance of eighteen inches from the trunk, and divided into two, and at a distance of four feet dipped into ground. The tree appeared to have been buried in mud before decay commenced, and to that circumstance was due probably its preservation from further decay, portions of trunks and branches were strewed around. We obtained a photograph and forwarded it to the Illustrated London News, in which paper an engraving appeared at the time. It was, we believe, a sigillaria, but was smooth, and shewed few of the marks common to the genus, such as appear on the accompanying enlarged section of the upper part of trees of a like kind. The roots also were smooth as far as exposed. The rock in which the roots were embedded was the Crawstone crust, and the sandrock which surrounded it was highly charged with oil or petroleum, derived from the vegetation which had produced the seam of coal, (the little flint coal) above, or from the decaying trees and branches of trees which now lie prostrate, and are embedded in the rock itself. There is one of considerable size at the time we write, five feet of which is exposed to view, the other part is obscured by the rock; and at the upper end where it enters the rock is a soft brown substance, about an inch thick, with impressions of the woody fibre of the tree itself. It is just that kind of fleshy substance one would suppose to belong to such trees, and one can scarcely resist the impression that it is the bark. Examined by the lens it appears to be thickly studded with small white crystals, strewed about.
Interlacing each other are Calamites, the giant representatives of our mares-tail which still flourishes near in damp places on the surface. The following representation will afford an idea of the gigantic proportions they then attained. They are to be found at all stages of growth; sometimes with their central pith, surrounded by a ligneous cylinder, divided by medullary rays, and having a thick bark. These reed-like plants were of course suited to the moist condition then prevailing, and assumed magnificent proportions.
The following is the section as it now appears, commencing at the surface and taking the measures in a descending order.
Below the turf,—
| ft. | in. | ||
| 1 | Yellow clay | 4 | 0 |
| 2 | Coal Smut; (might represent Sill, coal) | 1 | 0 |
| 3 | Clunch | 1 | 0 |
| 4 | Vigor coal | 0 | 10 |
| 5 | Ganey coal rock (shale) | 1 | 0 |
| 6 | Ganey coal | 1 | 3 |
| 7 | Linseed earth (A brown soapy kind of clay) | 1 | 0 |
| 8 | Best coal and middle coal (These are separated by a parting which diminishes from 10 inches on the west to 2 in. on the east.) | 2 | 0 |
| 9 | Fine clunch | 1 | 0 |
| 10 | Clod coal | 2 | 0 |
| 11 | Clunch with roots and plants, and nodules of ironstone at bottom | 5 | 0 |
| 12 | Little flint coal | 2 | 0 |
| 13 | Little flint rock (with prostratetrees and petroleum) | 27 | 0 |
| 14 | Crawstone crust, with upright trees and roots embedded. | ||
| Total | 49 | 11 |
Beds of underclay so invariably accompany seams of coal that some have come to the conclusion that there was no exception to the rule. Here however is one, in the case of the Little Flint coal, which lies immediately upon a sand rock. Evidently it was not formed like peat from vegetation which grew and accumulated on the spot. There is no underclay to support the roots of ordinary coal-measure plants, but the coal follows closely the contour of the rock on which it lies; as though it had flowed over it and had been laid down upon it like a sheet of bituminous matter. And there is not the least doubt but that this was the case. Sigillarias, Lepidodendrons, Calamites, and tree-ferns flourished on the slime now hardened into shale, and which shows sun-cracks, and worm-burrowings, indicative of the then surface, with tracks of locomotive mullusca, as they dragged their shells along the soft impressionable slime. Heavy tropical rains then falling upon some upraised and exposed Caradoc or perhaps Millstone grit lands, the latter scarcely yet consolidated, brought down and held in suspension a quantity of sand which, as it settled down, formed a bed varying from three to thirty feet in thickness. The body of water which contained so much sand must, of course, have been much greater, and would probably cover the whole of the vegetation. The result was that the lower parts of the largest trees which were buried first were preserved in situ. The upper parts toppled over and lay embedded in the sand, as we find them. In both cases the vegetable matter decayed and was replaced atom by atom with fine sand; but the vegetable tissues, oil, and seeds, being lightest, rose above the sand, forming a pulpy bituminous plastic bed, which first fermented, and then crystalized into coal. Even the little disc-like seeds of the sigillaria, which make up a considerable portion of the coal, and which floated with other matter, lie flat and parallel with the lamina of the coal itself.
Nor is this the only instance of the kind. The Top coal of Halesfield and Kemberton shews signs of liquefaction; portions of fish, such as teeth, bones, and scales being embedded in the coal.
We ought to add in connection with the Black Rock section that the five feet of clunch over the Little Flint Coal is the underclay for the Clod Coal, and is full of roots and rootlets.
The descent from the Crawstone crust to the Silurian shale of the Dale cannot be traced. As passed through at the Limestone pit at Lincoln Hill, it was as follows:—
| Ft. | In. | ||
| 1. | Crawstone Measure Crust | 1 | 8 |
| 2. | Rock | 10 | 6 |
| 3. | Coal Smut | 0 | 9 |
| 4. | Clunch with balls of Sandstone | 12 | 0 |
| 5. | Lancashire Ladies’ Coal | 0 | 6 |
| 6. | Strong Clunch with Sandstone balls | 19 | 0 |
| 7. | Sandstone Rock | 10 | 6 |
| 8. | Chalkstone | 12 | 0 |
| 9. | Limestone (Silurian) | 28 | 6 |
| Total | 95 | 5 | |
This then may be considered a fair representation of the remainder of the measures which occur below those seen on the surface at the Black Rock Quarry; but the passage from the carboniferous to the Silurian formations is no where conformable, and no mention is made of the Millstone grit, a portion of which certainly intervenes, and which is to be seen in small patches near, but which might possibly be represented by the three or four last measures in the section of the Lincoln Hill Limestone Shaft.
Excellent opportunities occur in this immediate neighbourhood of studying the junction of the Silurian and Carboniferous formations, and of the evidences afforded of the denudation of the one prior to the formation of the other. To the general reader these words may convey little meaning, but the scientific student who studies the evidences here made clear cannot fail to comprehend the fact that he has before him not only an old sea-bed, rich in relics of the fauna which inhabited its waters, but a sea-bed which had become a cliff, and had in turn been gradually cut down and wasted during successive ages prior to that at which a carboniferous flora had begun to flourish. Two series of rocks are here in juxtaposition, yet so widely separated by time, as to indicate a gap in the consecutive history of the earth as great as if we were to blot out the intermediate history of this country from the close of the Heptarchy to the reign of George III.; only that the period of time in the latter case would bear no manner of comparison with the former. If we suppose the Wenlock limestone to have been once covered at these points by the Ludlow limestone, and this again by the old red sandstone—as is the case to the south, to say nothing of the carboniferous limestone and millstone grit, we are forced to the conclusion that thousands of vertical feet, and hundreds of cubic miles of solid ground were first piled up and then cut down and carried away by the sea. Creation itself in the interval of their formation passed through many phases, during which new species came slowly into being and disappeared, and were again replaced by others. To fill up the gap that succeeds this great silurian flooring of the coal-measures, to study the intermediate links of the missing strata we must go to the millstone grit in its undenuded or partially denuded state, as it occurs beneath the coal-measures of Little Wenlock, or at the bend of the road, called “The Turn,” in going from Coalbrookdale to Wellington.
The first thing striking the attention is a buff coloured shale, weathered on the surface to clay, at the base of the bold bluff cliff of gritty sandstone so conspicuous on the brow of the hill. Whilst examining this member of the Silurian series a man from a neighbouring cottage remarked, “That is fuller’s earth; persons fetch it when they are galled, and it is good for the eyes; large quantities are fetched away and sent to Manchester.”
The fossils it contains show that it belongs to the lowest member of the Ludlow group, and that the whole of the Aymestry and Upper Ludlow have been stripped off and washed away before either the millstone grit or the coal-measures were formed.
Among the fossils yielded by this shale, in addition to bivalves and corals, are those interesting forms of crustaceans called pen fossils, from their resemblance to a quill pen. The species we found was Graptolithus priodon, described in the early works of Murchison as Graptolithus Ludensis. The trilobites, from the fineness of the material, are so sharply and beautifully preserved that the visual organs of the little creatures are clearly discernible, even to the optical tubes, elongated cones, or crystaline lens such as are to be seen so marvellously distinct on the eyes of the dragon-fly of the present day. The beautiful markings too on the shield of these wondrous little creatures which flourished in these seas, in such numbers that they may be got out in groups—forms which died out and perished before the close of the carboniferous formation represented above it—are so delicate and fine as to equal if not to defy imitation in ordinary materials in use at the Dale Works; and it is we fancy at least worth the experiment whether with this shale reduced to powder it might not be made to produce delicate impressions after the example here set by nature. We also found here some beautiful Lingula, a Patella, an Orbicula, a Leptæna, a Lituites, a Fienestella, and other fossils. To inhabitants of the Dale, here is a field of research open which they may make their own, close to their own doors.
This fine earth is known by various names where it occurs in Shropshire and the adjoining county of Herefordshire. In the latter county it is said to be used by country people for cleansing purposes, in which case it is called “Walker’s earth or soap.”
If the reader will follow this soft soapy shale, as we did, higher up into the coppice, he will find large masses of rock which have been toppled over through the shale giving way. A slip on the side of the narrow path discloses a bed of it, and immediately above it, consequent upon a former slip, we come upon a sandstone rock from twelve to fourteen feet thick, with quartz pebbles, representing the millstone-grit. Then a bed of black shale occurs, about six inches thick, which is chiefly made up of coal-plants, some of which are converted into charcoal. These plants do not appear to have grown on the spot, but to have been drifted into their present position. They were evidently in a soft and yielding state, some of them being pressed quite flat. 318 One good sized slab opened with a cast of a Lepidodendron, and we met with another cast, clearly of the same tree, a short distance west of it. Another, a Sigillaria, was much more distinct, the leaf scars being quite sharp, and the fibres of the inner bark very clear. This interesting band of coal shale is succeeded by another of yellowish clay, of about equal thickness; and these are followed by a second and a third band of black shale, with alternate ones of yellowish clay. Above these are thick sandstone rocks, some white, and some coloured red by iron, which here and there occurs in the form of hematite.
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.
There were inequalities of surface then as now. The country had its uplands and its valleys, its rivers and its lakes, its dry and damp soils, its cool and sunny spots, but with one general genial climate reigning over all.
We have said on page 284 that Mr. Cranege lived in the house Mr. Moses now lives in. It should have been, where Mr. W. Hughes now lives, opposite the Wesleyan chapel.
In mentioning this chapel we might add that the Rev. John Fletcher assisted in its erection, working and carrying stones like another man, with his coat off.
The lease for the ground was obtained by John Share from Mr. Reynolds. Mr. Reynolds told Share he might make out the lease for 99 years. Share made it out for 99 years and added “and one year more.” Mr. Reynolds said “Share thou art deep, but I’ll sign it.” The lease has recently expired and the building has been handed over to the Conference.