nearly coinciding with the main road from Lilleshall to Watlingstreet, near Wellington, and thence by the Wrekin; on the west the boundary is formed by the elevated ridges of Benthall and Wenlock, broken by the gorges of the Severn, and on the southeast by the road from Much Wenlock to Bridgenorth.

The coal measures consist of the usual alternations of shale and sandstones with coal, having an aggregate thickness of 250 yards in 135 beds. The average thickness of the coal seams is about three feet, varying in number at different pits, from one to fifteen. The upper seams are thin, generally sulphurous, widely separated, and extremely irregular. The lower seams are nearer together and more persistent. The shales contain layers of ironstone: some of the limestones of this coal field are of fresh water origin, and contain the Unio in great quantities. These alternate with other bands containing marine shells, Nautili, Spirifera, and others: a many very remarkable fossils also occur in the nodules of ironstone, which are very common here.

This coal field is much shattered by numerous and complicated faults; the largest of which tilt the strata in various directions. Those faults, on the east and west, bring the coal strata on a level with those of the permian formation, through which the whole coal field has been upheaved; only the lower members of the permian system have been found in the neighbourhood. They pass comformably into the coal measures below, and some of the upper strata are unconformable to them.

3-Plain of Shrewsbury.

West of Colebrookdale there are some detached and much broken coal fields, the most important of which is a curvilinear zone, extending from the north-eastern flank of the Brythen hills to Wellbatch, near Shrewsbury. The carboniferous strata rest on the inclined edges of the Silurian rocks, and dip towards a common centre, beneath the new red sandstone. Detached portions of the same zone occur at Sutton and Uppington, and these follow the sinuous outline of the northern flanks of the Longmynd and Caer Caradoc; three thin beds of coal are for the most part observable. At Pitchford the whole carboniferous series is described by Mr. Murchison as represented by a bituminous shale of only a few feet in thickness. The coal measures of this district contain a band of fresh water limestone, like that of Colebrookdale, containing the same fossil shells; the strata here pass up conformably into the base of the permian sandstones.

4.-Clee Hills.

The Brown Clee, and the Titterstone Clee Hills, which rise a few miles south of Colebrookdale, afford several small coal fields, which are thrown up to a considerable height above the adjoining country of old red sandstone; these are more interesting from their geological relation to igneous rocks, than from their economical importance.

In the Brown Clee Hills the coal seams are thin, and, in the Titterstone Clee Hills, the principal bed has a thickness of six feet. The base of the coal-bearing strata is hard sandstone, sometimes passing into a conglomerate; the equivalent of the millstone grit rock, between which and the old red sandstone is a thin band of carboniferous limestone. The coal measures are for the most part covered with basalt. In the Titterstone Clee Hills, the dyke through which the basalt flowed may be clearly traced, and the coal strata are broken by a series of faults, upcast towards the point where the basalt found vent.

On the east of these hills, and between them and the Severn, is another small coal field, about eight miles long, extending southwards from Billingsley to the borders of Shropshire and Worcestershire. Coal also occurs at Over Arley on the Severn, and likewise in two small patches at Pensex, near the foot of the Abberley hills.

IV. SOUTH-WESTERN

COAL DISTRICT.

1.-Coal field of South Wales.

This great and important coal field extends from Pontypool to St. Bride's Bay, a length of a hundred miles; its greatest breadth in the counties of Monmouth, Glamorgan, Caermarthen, and point of Brecon, being nearly twenty miles, while in Pembrokeshire it is not more than five. This field is a vast double trough, having an included anti-clinal axis, ranging nearly east and west. The strata crop out on the north and south, and are skirted all round by a zone of carboniferous limestone, which emerges from beneath them. On the south the strata dip at an angle of forty-five degrees; but on the north the inclination does not exceed twelve degrees.

This district is also intersected by deep valleys, running north and south. It has also been subjected to great denudations. The Plutonic agencies, which have so contorted and dislocated the strata, have been shown, by Professor Ramsay, to have taken place at the close of the carboniferous period. The main trough contains by

far the greater portion of the coal measures, which basset north and south. The centre of the big trough runs under Newbridge (Monmouthshire), through the high ground into the Sixhoury valley, below Blackwood, thence into the Rhymney Valley, which it crosses at Craig Penalltane, and under the Gellygaer Hill, into the Taff Vale. The smaller trough is direct south of the larger one, and occupies all the distance between the great anti-clinal axis, and the southern crop of the basin. The beds of the south crop are more highly inclined than those on the north; they are also of much greater thickness, showing a tendency to thin out as they approach their northern limit.

The faults of the South Wales coal field are numerous, and often locally extensive. The largest faults are to be found in the northeastern part of Glamorganshire; running south-west from Merthyr, across the Gellygaer Hill to Llancaiach, where it is one hundred yards; so that the Mynyddswyln vein of coal, which is worked by level at Tophill, is obliged to be worked by deep pit, at the Llancaiach colliery, which is only a few hundred yards to the south. Another great fault runs westward from Trevethin, near Pontypool, to Blackwood, where there is a perfect chaos of faults, The whole of the south crop is much intersected by faults, particularly in the neighbourhood of Glamorganshire and Caermarthenshire, but their small size prevents their having any general interest. The principal seams of coal at Pontypool are the following:

The Troed-y-rhin coal is the highest in the lower measures, and occurs also at the base of the pennant rock; its general thickness is about two and a half feet, but in all the valleys it is much worked under different names, owing to its accessibility and constancy of position.

Above this coal lie the middle measures, or pennant rock; at Pontypool it is about eight hundred feet thick, and immediately above it lies the only upper measure seam east of the Taff. The Mynyddswyln vein is the seam from which the red ash, or home burning coal, is sent to Newport and Cardiff. At Vasteg, the coal thickens out to an aggregate of fifty-one feet; the rock vein, which is here called the Droydeg vein, thinning to six feet five inches; and the meadow vein increasing to seven feet. One small seam of coal, seldom above two feet in thickness, which lies immediately above the "Farewell Rock," is the most constant seam in the whole basin. It is known by ten or eleven different names, at different places where it is worked; its upper shales are characterised by fish remains, and the other veins by fossil shells of the genus "Unio," or "Anthracosia." There are also strata, containing Goniatites, Producta, Spirifera, &c.; these often occur in nodules of ironstone. The beds of coal are twenty-three in number, having an aggregate thickness of ninety-five feet. The southern side of the basin, from Pontypool to Caermarthen, yields bituminous coal. The north-eastern side, coking coal, and the north-western, stone coal and culm. There are also sixteen bands of iron stone; the most valuable of which is below the lower coal. The lowest bed of coal is seven hundred fathoms deep at the centre, and all the principal strata are from this to five hundred fathoms. The occurrence of iron ore, so near the coal, has led to the establishment of the great iron-works which have sprung up in this neighbourhood. When the iron trade was commenced here in 1560, by Richard Hanbury, a London goldsmith, the whole of the mineral property was let for nine shillings and fourpence! The rental now shows a value more like that of house-room in London.*

2.-Forest of Dean.

This is an irregular basin, having Coleford as a centre; the length from north-north-east to south-south-east being about ten miles. It is of a triangular form, bounded by the Wye, the Severn, and the road from Gloucester to Ross. The coal beds are about twenty in number, having a total thickness of about forty feet, and a workable area of 36,000 square acres. The dip of the strata is

towards the centre of the basin, The exterior ridges of limestone

and old red sandstone, prolonged across the Wye, form the mountainous tract between that river and the Usk.

3.-Coal fields of Somersetshire and South Gloucestershire. These fields occupy an irregular triangular area, extending from near Iron Acton on the north, to Coleford, at the base of the Mendip Hills, on the south, nearly twenty-five miles long; and from the Newton collieries, near Bath, on the east, to those of Bedminster, near Bristol, on the west; the course of the Avon nearly coincides with the shorter line, and divides the coal-field into two almost equal portions. The stratification has undergone much derangement, and is subject to great local irregularities, the beds being sometimes vertical, and even bent backwards into sharp and short flexures, so as to form within this area several smaller basins. This coal series is only denuded in a few places, as about Iron Acton, Brislington, Newton, the Vale of Pensford, near Clatton, and at Coleford. In other parts the coal is worked by means of shafts sunk through the overlying strata of new red sandstone, lias, and inferior oolite. This cover of newer rocks, combined with the irregularities in the dip of the beds, renders it very difficult to trace the series of deposits in these coal fields; but it is probable that there are between fifty and sixty seams of coal, some of them being very thin, and none of them more than a yard in thickness.

The millstone grit, in the neighbourhood of Bristol, is of a reddish colour, from the amount of iron it contains, and the mountain limestone is there generally of a greyish cast. Within a few miles of that city there are displayed, rocks of the lias, the oolite, the carboniferous limestone, and the upper coal measures.

V.-COAL FIELDS OF IRELAND.

These deposits are not so well developed as in England. The carboniferous limestone is tolerably prevalent in the interior, and is partially covered by carbonaceous deposits. These deposits extend one hundred and fifty miles in length, and one hundred and twenty in breadth. Coal has been found in seventeen counties, but not in any considerable quantity, nor, in general, of the best quality. These deposits are divided into four coal districts, named after the four provinces of Ireland. Connaught and Ulster produce the same sort of coal as is generally found in the Lancashire coal field; and Leinster and Munster produce anthracite, similar to that met with in the South Wales coal field. The South Munster coal