CHAP. 2. Geology. Principal to Geology, and displays the arrangement of the strata from Sheffield in This extension of strata, which may generally be traced throughout all their disruptions, is further exemplified in compartment (F) which is a very diminished representation of Mr. White Watson's delineation of the strata of Derbyshire, from Bolsover in the east to Buxton in the west. The similar numbers on each side the great disruption at Brampton and Combs moss, show the extension of similar strata that seem to have been certainly once united. The following are the names of the strata represented, of which the very limited scale of the plate will only permit us to mark the most important; and these we hope will suffice to give the reader a general view of this line of stratification, which is indeed all that we can attempt in a work of this nature. With these previous observations and references, it will not be difficult to understand the positions of the principal strata of Derbyshire. First, the gravel or alluvia of this county claims attention, as occupying In our list of the hills (page 8.) this eminence will be found to be one of the hummocks on the north ridge of the Noe. indiscriminately the surface of every other stratum. On the borders of Nottinghamshire, the gravel consists of alluvial sand and rounded quartz pebbles to the depth of above two hundred yards; and, in many parts, it is concreted into a soft gravel rock, or pudding-stone as some call it, and is irregularly stratified. Mr. Farey states, that in all his examination of this immense mass of gravel, he could not perceive, except upon the surface, a single pebble which belonged to the neighbouring strata, or to any stratum he had ever seen in England.* This vast mass of quartz gravel extends across Derbyshire into Staffordshire, leaving isolated patches of the red marl occasionally uncovered. It is sometimes mixed, in the middle district of the county, with sand and flints from the south-east, and with a few thin and partially rounded fragments of the Derbyshire mountain limestones, brought down by the Dove and Derwent rivers. The narrow valleys near Foremark and Bretby, and the sides of rivers and brooks, have generally an alluvial flat of loam upon the gravel, which produces excellent meadows. This foreign quartz gravel has lodged itself against dislocations of the strata and completed the regular form of the surface, as may be seen in the neighbourhood of Allestree, Mugginton and Ashbourn particularly. When mixed with clay and marl, the gravel frequently needs draining, and produces cold and rather poor lands. The surface of the county covered with this species of soil amounts to very nearly 77,000 acres. Rounded stones are essential to gravel, but in some instances the stones in alluvial mixtures are angular, and often resemble the larger chippings of a stone mason's yard. Large stones, rounded by attrition, are called bolders; but if they retain the original shape and angles of the block, they are called self-stones. Another class of alluvial substances is the slither or indestructible rubble of limestone: and patches of slither are the most barren spots that can be imagined, not a blade of grass, a weed, or even a lichen being found upon them. CHAP. 2. Principal Strata. 2. Red marl. The regular stratum, which, except where it is interrupt- Red Marl. ed by tracks or patches of gravel, covers the southern districts of Derbyshire, is called red marl. At a short distance north of Stapleford and Sandiacre, it crosses the Erewash, and extends from the eastern to the western boundaries of the county, passing near Stanton by Dale, Bredsall, Quarndon, Bradley, and Ashbourn. Its position is, in almost every place, very nearly horizontal; except that on the borders of Staffordshire near Stapenhill it dips to the north, and again at Stretton it inclines still more decidedly to the south-west. Experienced land-surveyors have remarked that the best tracts of land are upon this stratum; but the Derbyshire red marl is frequently found to be tenacious and cold, and to require draining, which, however, it amply repays. Bricks and tiles are made in great quantities from the more tenacious parts of this stratum. The surface of the red marl is much furrowed into valleys, disclosing the bassets of fine-grained micaceous gritstone, which become freestone quarries; and in some instances these beds are not concreted, but appear as sand, as at Normanton near Derby, Stepping lane, Radbourn common, &c. The red marl is also intersected with marl stones, in layers of a light grey or dingy green colour, • Farey Vol. I. p. 132. E CHAP. 2. particularly at Allestree, Breadsall, Littleover, &c. In Derbyshire, the red marl, according to the calculation of Mr. Farey, occupies about 81,000 acres of the surface. Red Marl. Magnesian Coal. 3. Yellow or magnesian limestone. These strata emerge first from under the mass of alluvial gravel in Nottinghamshire, and appear upon the borders of this county at Hardwick Hall and Hucknall, whence they stretch themselves across the north-eastern angle of the county by Bolsover* and Barlborough into Yorkshire. These important strata cover an immense series of coal measures, which basset from beneath them: they preserve a remarkably regular plane, having an easy dip to the eastward, and are of considerable thickness: their general tint is yellow, from a pale straw-colour to deep orange. They effervesce with acids only in those parts where they abound with magnesia, and are not generally found capable of calcination. In some places they are called clunch and mudstone, and perish gradually on exposure to the atmosphere. At Wild park, near Brailsford, and at Birchwood park near Norbury, patches of the yellow limestone strata are found, which appeared to Mr. Farey to be "very probable indications of a coal field. Beneath the regular strata of yellow limestone, there are found compact beds of blue limestone, imbedded in clay, and abounding with ammonia and other shells, and these differ in their properties from the yellow strata, and are found to be much more proper for agricultural purposes. The soil made by the yellow limestone strata is generally of a medium quality and degree of tenacity. It is much improved by applications of the Peak limestone, or of the lime from the blue beds beneath it. Mr. Farey considered it adapted for arable rather than pasture land, on account of its proneness to produce a sour grass called spiked fescue (festuca pinnata) which scarcely any animal will eat. In Derbyshire, the yellow limestone occupies nearly 21,000 acres. 4. Coal. The portion of the great Yorkshire and Derbyshire coal field or coal raket which belongs to this county, occupies a district of about twelve miles in width on its eastern side, and seems to be terminated on the south by that immense disruption of the strata, which Mr. Farey and other writers after him, have termed the great Derbyshire fault, already mentioned. By this disruption the coal measures are brought, in various places, from below the red marl and yellow lime, to a level with the red marl on the surface. This denudation of the coal is principally observable in the neighbourhood of Stanton by Dale, Stanley, Morley and Little Eaton. There is also another more irregular disruption of the strata which extends from Little Eaton to Kirk Hallam and West Hallam, and in this the ancient basset-pits or shallow workings appear. From the Hallams, this disruption spreads across the Erewash into Nottinghamshire, where the Bilborough and Nuthall coals, which are in some places worked below the magnesian * See Explanation of White Watson's Section, p. 48. "The Yorkshire and Derbyshire coal-field, commences a little north of Leeds, and extends in breadth east and west about twenty-five miles, from Halifax to Abberford, and in length about seventy miles, from Leeds to near Nottingham and Derby. The breadth decreases southward, being little more than twelve miles in Derbyshire. South-west of Derbyshire there are a few small coal-fields near Ashby-de-la-Zouch, and near Tamworth, Atherstone, and Coventry. The latter coal-field is the most southern situation in which mineral coal has been discovered in the midland counties." Bakewell's Introduction, p. 496. lime, rise almost to the surface. This disruption may be considered as the CHAP. 2. eastern boundary of the coal field: from Nuthall it takes a turn towards Coal. the north, it again enters Derbyshire near Pleasley; and at Palterton and its neighbourhood, coals have been worked under the yellow lime, and are so worked at Clown. At the western end of Barlborough, this irregular disruption touches the edge of the yellow lime and leaves no space for the basset of the upper part of the coal measures, but a little further to the north-east, there are the Knitaker or Knittacar collieries, which are worked both in the bassets and through the yellow lime. At the Pebbley and the Killamarsh mines, the eastern boundary of the great coal field enters Yorkshire. From the line of irregular disruption thus pointed out, the coal measures to the westward take a more rapid rise towards the districts of the High Peak. These continue to rise, with some local varieties and exceptions, until all the vast series of coal measures have basseted, and the first or millstone grit appears from under them along a line which may be traced from Little Eaton through or near Belper, Crich, Tansley, Darley, Beeley, Chatsworth, Curbar, Fox-house, and so on to Hallam in Yorkshire. Within this coal-field, and sometimes beyond its boundaries, there are denudations displaying detached portions or hummocks of coal measures, which often appear to have been torn from other places. Thus, at Ashover, the coal-shale with other strata have been stripped off from the grit and limestone shale; while the coal around Alderwasley seems to have been torn from the grit which lies naked near Crich, where the channel of the Derwent divides these coal measures from those at Lea. This denudation is still more remarkable at Belper, where detached coal measures are to be found in the deeply excavated vale of the Derwent. Isolated patches of coal are found at Combes Moss, a mountain of shale and grit, nearly north of Buxton, and there is evidence that similar and more extensive patches might be found on the Kinderscout range, north of Edale Chapel, concealed under the impassable peat bogs, which abound in that district. The branch of the coal-field which extends into Leicestershire, may be regarded as a series of disruptions which has lifted up the yellow limestone and the coal strata through the red marl; the two former having rapid dips, while the marl preserves its usual horizontal position. It is in this branch that the collieries are formed at Gresley, Hartshorn, Measham, Donisthorpe, Newhall, Swadlingcote, &c. Before we give a list of the collieries in this county, or describe the different manner of working them, it will be serviceable to extract the following passage from the work of Mr. Bakewell." Coal-fields are of limited extent, and the strata frequently dip to a common centre, being often arranged in basin-shaped concavities, which appear to have been originally "The mountains of transition limestone which extend through the Peak of Derbyshire, and through Craven in Yorkshire, abound exclusively with the organic remains of marine animals. They are covered on the eastern side by two thick beds, which contain carbonaceous and bituminous matter and vegetable impressions. The lowest is from 150 to 170 yards in thickness. It is called by Mr. Farey limestone shale, because it occurs over limestone. It is composed principally of thin strata of shale and sandstone. Where it is exposed to the air, it is of a dark reddish brown colour; over this lies a bed of coarse-grained siliceous sandstone, not less than 130 yards in thickness. It has been called millstone grit by Mr. Whitehurst, and the miners in the north of England, from being used for the purposes of millstones. These two beds separate the metalliferous limestone from the coal strata in that part of England; for though thin seams of coal sometimes are met with in them, they do not contain any of sufficient thickness to be worked." Bakewell. Coal. CHAP. 2. detached lakes, that were gradually filled by repeated depositions of carbonaceous and mineral matter. In some of the larger coal-fields the original form of the lake cannot be traced, but in the smaller ones it is distinctly observed. The different strata under a bed of coal are frequently similar to the strata over it; and the same series is again repeated under the lower beds of coal, and sometimes with a perfect similarity both in the succession and thickness of each.* In some instances, a single bed of stone of vast thickness, separates two beds of coal. In other instances, only a very thin stratum of shale or clay lies between coal beds.-Though numerous beds or seams of coal occur in one coal-field, very rarely more than three of these are worked. The thickness of the coal strata in the same coal-field often varies from a few inches to several yards; but each stratum generally pre Frequently are readers disappointed in perusing topographical works, for the want of a few words of scientific explanation; and no county in England requires such explanation more amply than that which we are now describing. We shall, therefore, offer no apology, for extracting the following elucidations from the work of Mr. Bakewell, respecting coal-fields or basins, which by reference to the Geological plate, will enable strangers to visit our coal districts with much more gratification to themselves.—Coal strata are frequently bent in concavities, resembling a trough or basin, dipping down on one side of the field and rising on the other. In the Geological plate, (compartment D) the section of a coal-field is represented in which the coal strata c, c, d, d, are inclined in this manner, but partially dislocated by a fracture or fault at f. The extremities of the farther strata c, e, are several miles distant in some coal-fields, in others not more than one mile. **** The depth of the coal strata is very different in different situations, and from the inclination or bending of the strata, differs much in the same district, as will be evident from what has been stated, and from the inspection of the plate. On the eastern side of England, the strata generally decline, or, in the miner's language, dip to the south-east point: on the western side, the strata are more frequently thrown into different and opposite directions, by what are called faults and dykes. ✶✶✶✶ A dyke is a wall of mineral matter, cutting through the strata in a position nearly vertical. ...... The thickness of dykes varies from a few inches to twenty or thirty feet, and even yards. The dykes which intersect coal strata are composed of indurated clay or more frequently of basalt....... In some coal-fields the strata are raised or thrown down on one side of a dyke one hundred and fifty yards or more; and the miner, after penetrating through it (see Geol. plate, compartm. E) instead of finding the same coal again, meets with beds of stone or clay on the other side at e: hence he is frequently at a loss how to proceed in searching for the coal which is thus cut off. If the stratum of stone e be the same as any of the strata which are sunk through in making the pit or shaft g, g, it proves that the bed of coal is thrown down on the side of the fault at e, and he can determine the exact distance between that stratum and the coal he is in search of. But if the stone is of a different kind to any which was above the coal c, c, he may be certain that the strata are raised on that side; but to what distance can only be ascertained by trial, if the under strata of the coal bed c, c, have not been previously perforated. It frequently happens, however, that two or more strata of stone or shale at different depths, are so similar in their quality and appearance, that it is impossible to distinguish them: in such cases it is necessary to perforate the stratum, to ascertain its thickness, and examine the quality of the strata above or below it, by which its identity with any known stratum may generally be ascertained. The manner in which the strata are inclined towards the fault, will also determine whether they are thrown up or down, provided they are not shattered where they come in contact with it, which is frequently the case. Each bed of coal in a coal-field has certain characters by which it may generally be known to be the same. Its thickness and the quality of the roof and floor, with that of the upper and under strata, generally serve to identify it, though it may sink deeper in one place than another, and vary in distance from the surface 500 feet. .... The dykes which intersect coal strata are generally impervious to water; and it not unfrequently happens, that where the strata decline to them, they hold up the water and occasion springs at the surface, or keep the coal-works on that side of the fault under water, when the coal-works on the other side are dry. This will be better understood by consulting the Geol. plate, (comp. D and E) where the coal strata on the right hand of the faults decline or dip to them; and the water which passes through or between the strata will be stopped at the faults and held up, should any of the lower strata be also impervious, in which case the coal beds to the right of the fault will be under water, and those on the other side dry. Now should a perforation be incautiously made through the dyke, all the water will be thrown upon the works on the left, that were before dry. Where the wall on each side of a fault belongs to different proprietors, a few strokes with a pickaxe may thus do incalculable mischief to those on the one side, and render great service to the other, by laying their pits dry." |