The following arrangement is that of Messrs. Conybeare and Phillips, and from its simplicity will serve as a plan for some general remarks on the coal-fields of Great Britain:-1. The great northern district, including all the coal-fields north of the Trent. 2. The central district, including Leicester, Warwick, Stafford, and Shropshire. 3. The western district, which may be subdivided into north-western, including North Wales; and south-western, including South Wales, Gloucester, and Somersetshire.

Coal-District North of the Trent.-This great coal formation encircles the whole Pennine mountain chain on the east, south, and north; not however in one uninterrupted line, but in a series of detached coal-fields. 1. The Coal-Field of Northumberland and Durham. 2. Some small detached Coal-Fields in the North of Yorkshire. 3. The Coal-Field of South Yorkshire, Nottingham, and Derby. 4. The Coal-Field of North Stafford. 5. The South Lancashire Coal-Field. 6. The North Lancashire Coal-Field. 7. The Whitehaven Coal-Field.

1. The Coal-Field of Northumberland and Durham commences near the mouth of the river Coquet on the north, and extends nearly to the Tees on the south. As far as Shields the sea is its boundary on the east; from that point it leaves a margin of a few miles between it and the sea, and extends about 10 miles west from Newcastle. Its greatest length is 58 miles, and its greatest breadth about 24 miles. The coal-measures of this field rest on the series of strata of the millstone grit and shale, and are in part under the magnesian limestone, the northernmost point of which is near the mouth of the Tyne. The beds of which this coal formation is composed dip towards the east and crop out towards the west, so that a section of them gives the idea of a form of a boat. In consequence of this disposition the beds of coal in some places appear at the surface, while in the middle of the basin they are at great depths. At Yarrow, about five miles from the mouth of the Tyne, one of the thickest beds, called the High Main, is 960 feet deep, and rises on all sides; the dip of the strata averages one inch in twenty, but this is not uniform throughout; and therefore that bed does not rise to the surface at equal distances around Yarrow. The beds of the coal-measures are 82 in number, and consist of alternating beds of coal, sandstone, and slate-clay; making an aggregate thickness of 1620 feet, which varies however in different parts. The irregularities of the surface do not affect the dip or inclination of the strata; so that when a valley intervenes they are found in the sides of the opposite hills at the same levels as if the respective strata had once been continuous. It is difficult to determine the exact number of beds of coal, in consequence of the different depths at which the same bed occurs, the numerous faults, and the varying thickness of the beds of coal and other strata. These strata occasionally enlarge and contract so much, that it is only by extensive observation that the identity of the seams can be ascertained. Dr. Thomson supposes the whole number of beds of coal in this field to be twenty-five; Messrs. Conybeare and Phillips state that forty beds of coal have been seen: a considerable number however of these are very thin. The two most important beds are those distinguished by the names of High Main and Low Main. The thickness of the first is 6 feet, and of the second 6 feet 6 inches. The Low Main is about 60 fathoms below the High Main. Eight other beds of coal occur between these: one called Bensham is 4 feet thick, and another called Coal-Yard is 3 feet thick. Seven beds of coal have been observed under the Low Main, some of which are of considerable thickness, but of an inferior quality. The aggregate thickness of the whole number of seams is about 44 feet; but there are eleven beds not workable, the thickness of some of them being only a few inches. Five others amount together to only 6 feet. Making proper deductions for these, it may be considered that the available beds amount to 30 feet in thickness.

The number of dykes or faults which traverse this field is very considerable. They appear to run in all directions. The most remarkable, called the Great Dyke, or 90-fathom dyke, has received the

latter name because the beds on the north side of it have been thrown down 90 fathoms. Its direction is north-north-east and south-southwest. It enters the sea a little to the south of Hartley, or about three miles north of Shields, and running westward crosses the Tyne at Lemington, about four miles west of Newcastle Bridge. In some places it is only a few inches wide, but in Montagu colliery it is 22 yards wide, and is filled with hard and soft sandstone. From the southern side of this dyke two others branch off, one to the south-east and the other to the south-west. The latter, called from its breadth the 70-yard dyke, is also filled with hard and soft sandstone. This dyke intersects the upper or Beaumont seam of coal, but does not alter the level on either side. The thickness of the seam however decreases, beginning at the distance of 15 or 16 yards from the dyke: and the coal first becomes sooty, and at length assumes the appearance of coke. The south-eastern branch is only 20 yards in breadth. Another dyke, which passes through Coaley Hill, about four miles west of Newcastle, is about 24 feet wide. It is filled with basalt'in detached masses, which are coated with yellow ochre; a thin layer of indurated clay is interposed between the sides of the fissure and the basalt. The upper seam of coal is here about 35 feet from the surface, and where it is in contact with the dyke is completely charred. Another dyke, which crosses the Tyne at Walker, and traverses the Walker colliery, does not alter the level of the strata, but on each side of it the coal is converted into coke, which on one side in some places was found to be 18 feet thick, and on the opposite side only about 9 feet. At Walbottle Dean, 5 miles west of Newcastle, a double vein of basalt crosses the ravine in a diagonal direction, passing nearly due east and west; it underlies at an angle of 78 degrees, and cuts the coal strata without altering their dip, but the seam of coal is charred. A dyke, called the Cockfield Dyke, 17 feet wide, throws up the coalmeasures on the south 18 feet. The Low Main coal, contiguous to the basalt, is only 9 inches thick, but enlarges to 6 feet at the distance of 150 feet from it; the coal contiguous to the dyke is reduced to a cinder. The dykes, if not large, are locally called troubles, slips, or hitches. These minor faults are numerous and extensive, and are a perpetual source of difficulty and expense to the coal-owner by disturbing the level of the strata and by the disengagement of carburetted hydrogen gas. They are not however without their use, being often filled with a tenacious water-proof clay, by which numerous springs are dammed up and brought to the surface. The faults which depress the strata have kept valuable seams within the basin, which would otherwise have cropped out and have been lost.

The coal-field of Northumberland and Durham supplies an enormous quantity of coal. Besides being consumed in its own district, London depends nearly altogether on it, as well as all the southern coast counties, with the exception of Cornwall. It is consumed along the eastern coast, including all the eastern counties as far west as Hull, Boston, Peterborough, Bedford, and Windsor. An inquiry as to the probable duration of this supply is one of no small interest. Dr. Thomson calculates that this coal-field may fairly be expected to yield coal for 1000 years, at the annual consumption of two millions of chaldrons; but as we have no data by which to discover how much coal has been already consumed, we cannot tell how much of these 1000 years has already elapsed. Besides this, Dr. Thomson has taken the average annual consumption much too low for the present time. The coals shipped from the Tyne, the Wear, and the Tees, in 1835, amounted to 4,368,144 tons. The quantity of waste coal is estimated at one-third of the whole. Without therefore taking into account the consumption of the immediate district, the annual quantity of coal taken from the mines is more than 6,552,216 tons. On the other hand it appears that in this calculation the area of the coal-field is very much under-estimated, being taken at 180 square miles. Professor Buckland, in his examination before the House of Commons, limits the period of supply at the present rate of consumption to about 400 years. Mr. Baily, in his Survey of Durham,' states the period for the exhaustion of the coal to be about 200 years hence. Some proprietors of the coal-mines, when examined before the House of Commons, in 1830, extended the period of exhaustion to 1727 years. They assumed that there are 837 square miles of coal strata in this field, and that only 105 miles had been worked out. The small coal taken out of the pits is not considered worth shipment; large quantities of it were therefore often piled up near the mouths of the pits. These masses of coal were frequently set on fire, and burned for several years. Dr. Thomson describes two of these immense fires which were burning in 1814. About three miles to the north of Newcastle, and three miles off the road from Berwick, on the left hand, "one has been burning these eight years. The heap of coal is said to cover twelve acres. The other, on the right hand, is nearer the road and therefore appears more bright: it has been burning these three or four years (1814)." Of late years many more manufactories have been established in this district, by which, and by converting it into coke, most of the small coal is consumed.

Besides this coal-field there is another coal formation in the northern counties, which is minutely described by Dr. Thomson in the 'Annals of Philosophy,' November, 1814, under the name of the Independent Coal Formation. This tract terminates westward at Cross Fell, in Cumberland, is supposed to occupy the whole of Durham, and constitutes the whole of that part of Northumberland east of the Cheviots

exclusive of the coal-field already described. The different strata of this coal formation amount to about 147. The coal-measures here differ from those we have just noticed, in having limestone as well as sandstone and slate-clay alternating with the beds of coal; the coal worked in this formation is slate-coal, and is considered inferior in quality to the Newcastle coal. There are several collieries, but the coal is only employed for home consumption. The lowest bed of these measures crops out near Cross Fell. The coal of which it is composed, provincially called crow-coal, falls into powder when exposed to the air, and cannot be burnt by itself. The poorer class make it up into balls with clay, and use it for fuel. This bed is 387 fathoms below the lowest of the Newcastle beds. (Ann. of Phil.,' vol. iv.) There are numerous lead mines in this tract.

2. Detached Coal-Fields in the North of Yorksire.-These are very limited in extent, being small insulated coal basins, lying in hollows in the gritstone. They occur near Middleham, Leyburne, Thorpefell, near Burnsell, and as far west as Kettlewell. The seam is seldom more than 20 inches thick. At Thedswell Moor the lowest seam is one yard, but the stratum diminishes and vanishes at the edges. Messrs. Conybeare and Phillips doubt whether these beds should not be referred to the thin coal seams subordinate to the millstone grit series, rather than to the principal coal-measures.

Coal is wrought in some parts of the great carboniferous chain extending from Penigent to Kirkby Stephen. Here the great 'Craven fault' occurs, described by Professor Sedgwick ('On the Carboniferous Chain from Penigent to Kirkby Stephen,' in Geol. Trans.,' vol. iv. series 2) as ranging along the line of junction of the central chain with the skirts of the Cumbrian system, passing along the south flank of Casterton Low Fell, up Barbondale, thence across the valley of Dent through the upper part of the valley of Sedbergh, and along the flanks of Bowe Fell, and Wildboar Fell, to the ridge which flanks Ravenstone Dale. Throughout the whole of this line there are enormous and most complex dislocations, which affect the strata of the coal formation and produce other phenomena. Only one of the coal strata in the lowest part of the coal-measures is sufficiently valuable to be worked; it varies from 18 inches to nearly 4 feet in thickness. At Turna Fell, near Hawes, in Yorkshire and at Tan Hill, near the highest part of the road from Brough to Argengarthdale, this coal is extensively worked, and is of good quality. The same seam is found near Kirkby Stephen. Horizontal drifts have been carried into this bed near the top of Penigent, of Whernside, and of Great Colm; but in these parts it is of bad quality and not fit for domestic use, being mixed with ferruginous and pyritous shale. This coal varies in thickness from a mere trace to 2 feet. It was once worked to some extent on the south side of the valley of Dent, by means of horizontal drifts under Great Colm. It was only a few inches in thickness, but said to be of so good a quality as to be in great request. About 70 or 80 years ago it was sent on pack-horses from this place as far as Kendal, for the use of blacksmiths' forges, &c. Kendal has long been supplied with fuel from the Lancashire coal-field; but this fact, of comparatively so recent a date, strongly illustrates the astonishing progress we have made in our modes of internal communication.

At the Barbon coal-pit in Westmoreland, a coal-bed of this series is likewise wrought; the lower part of it is however so impure as to be unfit for ordinary purposes, and is chiefly consumed in lime-works. The following is a section of the strata as occurring in the Barbon colliery :

The strata of the coal are in general much less regularly continuous than the strata of limestone. This however is not always the case. Some of the thin bands of coal here appear to continue with astonishing regularity. The following example is quoted from Professor Sedgwick. "At Cross Pits, in the valley of Dent, the coal seam under the 12-fathom limestone is divided, by a band of clay half an inch thick, into two parts, with distinct mineral characters; and the same coal seam, with exactly the same subdivisions, has been found in the mountain on the opposite side of the valley at the distance of 3 or 4 miles measured in a straight line. This seems to prove that a bed not more than a fraction of an inch thick was originally continuous throughout an area probably several miles in diameter." (Geol. Trans.' vol. iv. sec. 2, p. 101.)

east of Leeds nearly to Derby, a distance of more than 65 miles; its greatest width, 23 miles, is on the north, reaching nearly as far as Halifax to the west. On the south it extends towards the east to Nottingham, and is here about 12 miles wide; but in some parts it is much narrower The strata of these coal-measures range in the same manner as in the Northumberland coal-field, from north to south, dip to the east and rise to the west and north-west, in which directions the lowest measures at length crop out against the rocks of the millstone-grit series, which constitute the higher ridges of the Pennine chain. The strata of this coal formation are very numerous. There are 20 beds of gritstone at the least, some of great thickness. Most of these beds consist of grains of semi-transparent silex united by an argillaceous cement; the lowest of these beds is termed the millstone grit, beneath which no workable coal is found. Besides these gritstone beds there are numerous strata of shale (slate-clay), bind (indurated loam), and clunch (indurated clay), alternating with several beds of coal of different thickness and value. A hard argillaceous rock called crow-stone forms in some places the floor of the coal beds, and is supposed to be a variety of the clunch still more highly indurated. The numerous faults in this coal-field render it extremely difficult to ascertain the exact number and order of the coal beds. Mr. Bakewell (p. 884) states their number at 30, varying from 6 inches to 11 feet, and the total thickness of coal at 26 yards. This however he considers as only an approximation. Three varieties of coal occur in these measures: hard, or stone-coal, which burns to a white ash soft, or bright, which burns to a white ash; caking, or crozling, which usually burns to a red ash. The first is esteemed the best, and is in much greater demand than the others. The thickest bed is worked near Barnsby. In a pit near Middleton three seams are being worked; one at the depth of about 40 to 70 yards from the surface, another 38 yards lower, and the deepest from 28 to 32 yards deeper, making the whole depth from 106 to 140 yards. The upper seam is about 2 feet 8 inches thick, the middle seam from 2 feet 10 inches to 3 feet 4 inches, and the lower one from 4 feet 6 inches to 5 feet. The strata of this field are traversed by an immense fault commencing from Allestry, in the south, and running in a zigzag direction through the south and east part of the field; the rise of the strata is said to be much more rapid on the western than the eastern side of the fault. Besides this great fault there are many others which traverse the field in various directions, and create an inextricable confusion by the rise and fall of the different strata, rendering it almost impossible to trace distinctly the continuation of each bed. This coalfield supplies the coal for the important manufactures which surround it, and also, by means of inland navigation, the midland counties south and east of Derbyshire.

A little to the west of the coal-field already described, coal has been found in two places about half-way between Ashborne and Derby, but it has not been worked.

4. Coal-Field of North Stafford.-There are two detached coalfields: the one situated on the north-cast of Newcastle-under-Lyne, distinguished as the Pottery Coal-Field; the other at Cheadle, to the east of the first. The form of the Pottery Coal-Field is triangular. Its vertex is near Congleton, from which point the sides diverge to the south-south-east and south-south-west, running in each direction about ten miles; the base is estimated at about seven miles: Newcastle is nearly in the centre of the base. The strata dip from the two sides to the centre of the area. On the eastern side the inclination westward is estimated at one foot in four; on the other side it is still more rapid. Between Burslem and its eastern limit, nearly in the centre of the coal-field, it has been ascertained that there are 32 beds of coal of various thickness, generally from about 3 to 10 feet each; but the strata are in general much dislocated in this field. In the principal mines in this district coal is found at various depths, from 50 to 300 yards and more; there has been a mine worked at the depth of more than 400 yards. Some seams only 20 inches thick have occasionally been worked, ' they are seldom worked under 3 or 4 feet thickness.

The Cheadle Coal-Field is an insulated basin surrounded by and reposing upon millstone grit; it is about five miles long and three miles broad, and is of little importance.

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beds of calcareo-magnesian conglomerate. Great disturbances have however interrupted the regularity of this arrangement, and caused divisions of the coal-measures, which render it difficult to trace out the exact dimensions of the field. At Disley, in Cheshire, it bifurcates into two branches, having an intermediate ridge or "saddle of millstone grit, the eastern branch forming a trough, of which the strata crop out on both sides against the millstone grit." This part of the field is a long narrow strip joined to the main field at Disley, and extending thence southward fifteen miles to near Mearbrooke in Staffordshire. The strata of the western branch of this bifurcation, extending from Disley to Macclesfield, dip again to the west, but not at so great an angle as they rose, on the east side of the intermediate ridge. In other parts of the coal-field great faults occur, but it has not been sufficiently investigated by the geologist for them to be distinctly traced. Mr. Bakewell has investigated a small portion, which he distinguishes as the Coal-Field of Bradford: the result of his observations is found in the second volume of the Geological Transactions. This tract is rather more than two miles long, and little more than one mile and a furlong wide. It is situated on the river Medlock, a short distance east-south-east of Manchester. It is surrounded on every side, except the east, by the red-sandstone which prevails in the environs of Manchester. Beds of limestone pass under this and overlay the coal-measures, in which there are several beds of coal rising to the north, under an angle of 30°. One of these, near the centre of the field, is four feet in thickness. To the north of these inclined beds there is a considerable disturbance, and the direction of the beds becomes suddenly vertical. One of the vertical beds, together with its accompanying strata, bears so close a resemblance to the 4-feet coal above mentioned, that there is no doubt of their identity, and that the vertical stratum was, before the dislocation which severed them took place, a continuation of the first. With these vertical beds the coal-measures terminate on the north an interval of the red-sandstone succeeds for about 1400 yards, when coal-beds again appear, rising as before towards the north. All this indicates considerable faults and subsidences, which however cannot be accurately traced at present. The coal from the Lancashire field supplies Manchester, Liverpool, and the surrounding districts.

6. The North Lancashire Coal-Field is one of little importance. It lies midway between Lancaster and Ingleton; it is about eight miles long and six miles wide, but it has never been thoroughly examined, and its strata cannot be distinctly stated.

7. The Whitehaven Coal-Field is situated on the west coast of Cumberland, and extends from near Egremont, south of Whitehaven, to near Allonby on the north.

worked in the Bedworth mines, but there the first and second coalseams of Griff run together and form a 5-yard seam. The intermediate strata of shale which separate them at Griff are found in the eastern shaft to be 33 yards, and in the western 25 yards thick; but they gradually decrease as they proceed westward, till at length they entirely vanish.

3. South Staffordshire or Dudley Coal-Field, the principal in the central district, extends from Beverton, near Badgely, on the northeast, to near Stourbridge on the south-west. The greatest length is about twenty miles, and its greatest breadth, from Walsall to Wolverhampton, is about seven miles, but it is very irregular towards the south, being almost divided into two parts. The area, from actual survey, has been found to be about sixty square miles. The southern portion, extending from Stourbridge to Bilston, about seven or eight miles in length and four in breadth, has been fully investigated by Mr. Keirs, and described by him in Shaw's 'History of Staffordshire.' No satisfactory account of the northern portions of this field has hitherto been published; many coal-seams, of eight, six, and four feet in thickness, are worked in it. The southern portion is of much more importance, as it contains seams from 30 to 45 feet in thickness. This enormous thickness is however not one continuous seam, but a number of seams, divided by layers of what the miners call band, which are very thin beds of clay-slate. The working of these thick seams is not so profitable as might be supposed. The pillars left standing in order to support the high roof are estimated at about onethird of the whole coal in the bed, and the small coal left in the mine is about equal to another third, so that only one-third of the whole is at present taken out of the mine.

In the coal-measures of this district there is an absence of the millstone grit, carboniferous limestone, and old red-sandstone, which usually lie under the coal-measures. The coal-measures rest, in the Dudley Coal-Field, on the transition rock at once, without any intermediate strata: this singularity is likewise observed in the Coalbrook Dale coal formation.

The coal district in South Staffordshire is traversed from northwest to south-east by apparently a line of hills, but they are not absolutely continuous, though they have a uniform general direction. On examination, the hills on the north and those on the south of Dudley are found to differ entirely in their character. The northern chain consists of highly inclined strata of limestone, against the sides of which all the coal-measures crop out at a considerable angle, but come nearer a horizontal position as they recede from these hills. The other chain of hills, on the south of Dudley, is entirely composed of one mass of basalt and amygdaloid, and the coalmeasures preserve their usual level in approaching the hills, not cropping out as they do upon the limestone chain. Two opinions are entertained with regard to these basalt elevations: "they may be either the protruding edge of a vast basaltic dyke traversing the probable. The coal-measures on the south, near Stourbridge, appear to dip beneath the beds of the newer red-sandstone formation: the beds of this and of the Warwickshire coal-field dipping in opposite directions under the super-strata, give reason for supposing that they may extend continuously below this through the intervening space. The eastern side of the field, which extends a little beyond Walsall, is bounded by the same limestone with that of Dudley, and the coalmeasures are observed again to crop out against it, thus lying in a basin between these two towns. That the coal-beds rise towards the north, and the upper ones crop out while others continue under the surface, is very satisfactorily shown by the comparison of the strata in different collieries. At Tividale the main coal is 60 fathoms below the surface; at Bradley it is only 20; and the greater number of beds which cover the main coal at the former place have entirely disappeared before the main seam reaches Bradley; and farther to the north the main seam also crops out and disappears altogether. A very curious phenomenon takes place at Bloomfield colliery, to the south of Bilston, thus described in the 'Geology of England,' p. 412:

The Ashby Wold portion ranges from Swepston, four miles south of Ashby, to Bretby in Derbyshire: the inclination of the strata is towards Ashby; but between the out-crop of the beds and that town another crop has been traced near Brothorpe, dipping in a contrary direction. More than twenty coal-works have been opened on this line. The lowest shaft sunk is to the depth of 246 yards. One of the seams is from 17 to 21 feet thick. This great thickness is caused, it is supposed, by the running together of two or more seams-a circumstance which is known to occur in the coal-fields of South Staffordshire. The eastern portion of this district commences about a mile and a half north-east of Ashby, and extends about six miles in length, running parallel to the larger portion. The strata dip to eastnorth-east. In the pits belonging to Sir George Beaumont two coalbeds, each a yard and a half thick, are worked. On Coleorton Moor several coal-seams, which have been proved to lie above these, have been worked at the depth of 116 feet.

NAT. HIST. DIV. VOL. II.

Many faults or dykes occur in this field; they are usually fissures in the beds, filled up with clay, and very frequently the levels of the There is a great fault near

Bilston, which causes the dip of the strata to be reversed, the beds on the south side dipping south, and those on the north side dipping north this is however an unusual circumstance

Western Coal Districts.-The Coal-Fields of this division are disposed around the transition district of North and South Wales. The north-western district includes the coal-fields of Anglesey and Flint shire, the western those of Shropshire, the south-western those of South Wales, of South Gloucester and Somerset, and of the Forest of Dean.

1. Isle of Anglesey.-At the distance of about six miles from the Menai Straits, and running nearly parallel to them, a remarkable valley stretches across the whole island. This valley opens on the north into Red Wharf Bay, and on the south into the estuary of Maltraeth; it is flanked on both sides by parallel bands of carboniferous limestone, in the depression between which coal has been found, and it is thought probable that the coal-measures may extend through the whole line. Coal has been worked near the Maltraeth æstuary; and a few years since shafts were sunk in the neighbourhood of Trefdaeth. Successful trials have likewise been made at Pentreberen, about five miles north-east of the former pits: the beds are said to be of a tolerable thickness, and the coals of a good quality.

2. Flintshire. The Coal-Field of this county extends north and Bouth from Llanassa, near the western cape of the estuary of the Dee, to near Oswestry, in Shropshire, forming an exterior belt coextensive with the range of the mountain line from the north of the Clwyd. Where the carboniferous limestone is partially interrupted by the mountain of Selattyn the coal shales rest immediately on the transition slate, of which that mountain is composed. (Conybeare and Phillips, p. 419.) The greatest length of the district in which the coal-measures are found is about thirty miles, but it must by no means be understood that coal is worked throughout. At Oswestry there is a very small detached piece, not more than three miles long and half a mile broad; there is then an interval of some miles. Near Chirk another coal tract commences, and runs north for about five miles; then another interval occurs; and a little to the north of Wrexham the principal portion begins, and thence extends to the coast, and forms a narrow belt along it to the termination at the west cape of the Dee. The beds dip from one yard in four to two in three, sink beneath the estuary of the Dee, re-appear on its opposite side, and finally sink beneath the strata of the newer red-sandstone. This position of the coal-measures has led to the conjecture that they are connected with the beds of the Lancashire coal-field. The coal formation here commences with the same strata as those of Derbyshire. The beds of coal vary in thickness from three quarters of a yard to five yards. In the Baggalt mines three seams are worked, varying from 3 to 7 feet. Common, cannel, and peacock coal are found. 3. The Coalbrook Dale Coal-Field rests on transition rock: it extends from Wombridge, in the parallel of Wellington, to Coal Port, on the Severn, a length of about six miles; its greatest breadth is about two miles. The coal-measures are composed of the usual alternating strata, which occur without much regularity, except that cach bed of coal is always immediately covered by indurated or slaty clay, and not by sandstone. The strata are 86 in number. In Madely colliery a shaft is sunk 729 feet through all the beds. The first coal-seam, which occurs at the depth of 102 feet, is very sulphurous, and not more than 4 inches thick; nine other beds of a similar nature, but rather thicker, occur between this and the depth of 396 feet. This coal is called 'stinking coal,' and is only employed in the burning of lime. The first seam of coal that is worked is 496 feet deep and 5 feet thick. Two other beds of coal occur, one 10 inches and the other 3 feet thick, before the bed of 'big flint' sandstone, which is found at the depth of 576 feet: nine beds of coal occur, of the aggregate thickness of 16 feet, between the 'great flint' and the 'little flint' bed (an interval of 100 feet). Beneath the 'little flint' and the lowest bed of the whole formation there is a sulphurous 8-inch coal. This account of the strata refers more particularly to the Madely colliery. The coal of this field is usually a mixture of slate-coal and pitch-coal.

West of the Coalbrook Dale Field there are a few detached, narrow, and broken coal-fields in the plain of Shrewsbury, at the other side of the Wrekin.

Several small Coal-Fields occur in the Brown Clee Hill and the Titterstone Clee Hill, which rise a few miles south of the Coalbrook Dale Field; the latter hill is about four miles south of the former. The coals in the Brown Clee Hill only lie in thin strata, while the principal stratum in the Titterstone Clee Hill is 6 feet thick. The coal-fields on the Titterstone Clee Hill are represented as six detached portions, or separate basins, cut asunder and rendered irregular by a vast basaltic dyke, more than 100 yards wide, which intersects the hill. These coal-measures are more interesting to the geologist than

the miner.

On the east of these hills, and between them and the Severn, a Coal-Field extends from Dense Hill and Billingsley on the north to the borders of Shropshire and Worcestershire on the south, a length of about eight miles, coal being worked in several points along this line. Coal is also worked near Over Arley, on the Severn, adjoining this tract on the west. Only a few miles from the Billingsley coal-field at Pensex, near the foot of the Abberley Hills, is "a small patch (rather than field) of coal-measures," and another similar piece about three miles to the west.

The South-Western Coal District comprehends the several Coal-Fields near the æstuary of the Severn and the Bristol Channel, including parts of the adjacent counties of Gloucester, Somerset, Monmouth, and Glamorgan. The various coal-fields distributed over this district are apparently insulated, yet they have several points of connection. They all rest on one common base of old red-sandstone; they all appear to have been formed by similar agency and at the same era; to have been subject at a later period to the same revolutions; and lastly, to have been covered partially by similar overlying deposits." (Geol. Trans.,' vol. i.) The several basins in the coal formation are divided by lines termed 'anticlinal,' formed by the saddles of the strata or meetings at the surface of their vertical angles, on each side of which the strata dip in opposite directions. The coal-measures are

thus surrounded by exterior bands of mountain limestone and old red-sandstone, in the order of the outcrop of the subjacent beds. This district includes three principal coal basins, together with some smaller ones, adjacent to and closely connected with the two last. First, the South Welsh coal basin; second, that of South Gloucester and Somerset; third, that of the Forest of Dean.

1. The Coal-Field of South Wales is upwards of 100 miles in length, and the average breadth in the counties of Monmouth, Glamorgan, Caermarthen, and part of Brecon, is from 18 to 20 miles; it becomes much narrower in Pembrokeshire, being there only from 3 to 5 miles. This area extends from Pontypool on the east to St. Bride's Bay on the west, and forms a vast basin of limestone in which all the strata of coal and ironstone are deposited. The deepest part of the basin is between Neath and Llanelly: from a line ranging nearly east and west through Neath all the strata rise on the south towards the south, and on the north towards the north, cropping out at the edges. The limestone crops out at the surface all round the coal, except where its continuity is interrupted by Swansea and Caermarthen bays. The depths from the surface to the various strata depend upon local situations. The upper coal-seam does not extend a mile either north or south beyond Neath, and not many miles in an east or west direction, and its utmost depth is not above 50 or 60 fathoms; the next stratum of coal and those likewise beneath, being deeper, crop out at a greater distance from the centre; and so of the rest in proportion to their depth. The lowest bed is 700 fathoms deep at the centre, and all the principal strata lie from 500 fathoms deep to this depth. But this district is intersected by deep valleys which generally run in a north and south direction, intersecting the coal. By driving levels in the hills the beds of coal are found without the labour and expense of sinking shafts; there are also many pits in the low valleys. This basin contains twelve beds of coal from 3 to 9 feet thick, making an aggregate of 70 feet; and there are eleven more from 18 inches to 3 feet, together equal to 24 feet; the whole thickness is therefore 95 feet. A number of smaller seams likewise occur. On the south side of the basin, from Pontypool to Caermarthen Bay, the coal is principally of a bituminous nature; on the north-east it is a caking coal; on the north-west, anthracitic. It is this latter coal which has the greatest heating power. It is found in abundance near Swansea, and is cheap. Great faults occur in this field, which traverse it generally in a north and south direction, and throw the strata out of their level 40, 60, 80, or 100 fathoms. These dislocations are not often shown on the surface. A principal fault occurs at Cribbath, where the strata of limestone stand erect; another of considerable magnitude lies between Ystradvellte and Penderryn. These dykes are usually filled with clay, but one of some magnitude has been observed near Swansea, which is many fathoms wide and filled with fragments of the disrupted strata, the level of which differs by more than 240 feet. The rich ironstone of this basin supplies extensive iron-works in the neighbourhood. The principal beds of ironstone occur in the lower part of the coal-measures; the most valuable bed is found beneath the lowest coal. The strata of this coal formation dip much more rapidly on the south than on the north; on the south they make an angle of 45° with the horizon, and on the north dipping only 10°. The coal from the South Wales basin supplies the whole of Wales with the exception of the more northern counties, the whole of Cornwall, and the western half of Devonshire.

2. South Gloucester and Somerset Basin.-This basin occupies an irregular triangular space, bounded on the south by the Mendip Hills, which are a high range of mountain limestone resting on an arch of old red-sandstone. The vertex of the triangle is on the north, at the village of Tortworth in Gloucestershire: the western side from the Mendips to the vertex is formed by three insulated masses of high land, separated by narrow intervals, the widest of which is less than