Derbyshire into the south-western portion of Lancashire, by Manchester, to Prescot, near Liverpool; having Macclesfield on the eastern or opposite horn of the crescent, and Colne near its northern extremity; and the towns of Rochdale, Oldham, Bury, Bolton, Leigh, and Wigan within its area. The strata dip from the exterior, along with the millstone grit on which they rest, towards the inner edge of the crescent, beneath the Permian sandstones.* This general arrangement is, however, disturbed by many local dislocations. The coal field may be divided into three parts; the lower, the middle, and the higher. The lower portion contains three seams of coal, averaging about four feet in thickness, and has a superficial extent of 480 square miles. The middle portion contains two seams, averaging a thickness of three feet, with a superficial area of 480 square miles. The higher portion has an area of at least 100 square miles, containing about 70 seams of coal, with an aggregate thickness of upwards of 100 feet. Several seams of coal, in this field, contain aviculo-pectens, goniatites, and other marine shells in their upper shales: fish remains are also common in this coal field. The following are a few of the coal seams which have been most worked :

There are also several seams of cannel; and one seam of coal is ten feet in thickness, the aggregate thickness of coal being nearly 150 feet. This coal field runs under the new red sandstone, to join that of North Wales. The total thickness of the measures is about 5,000 feet. The Ardwick limestones are the highest series of the coal measures in Great Britain.

* Trimmer's Geology.

† Hall's "Introduction to Geological Map of Lancashire and Cheshire."

On cutting the railway from Manchester to Bolton, six fossil trees were discovered in the sandstones, the whole of the stems -standing at right angles to the plane of stratification; and had their roots extending into the rock around. The largest of these trees is about fifteen feet in circumference at the base, seven and a half at the top, and is eleven feet high. The others are of different circumferences, of from seven to three feet. They were Sigillariæ, and must have grown upon the spot where they were found fossilised; having been entombed by the sediments which had been drifted by the waves from the neighbouring shores.

5.-The Whitehaven Coal field.

This tract extends from Egremont on the south to Allonby on the north. It forms a narrow band skirting the north-western flanks of the Cumbrian mountains. On the banks of the Calder it is covered by the permian sandstones of the plain of Carlisle. A good section is displayed in the cliff of St. Bees, where, the dip being to the south, the coal measures are seen covered by the magnesian limestones, and that again by red marl. The largest seam of coal, in this coal field, is nine feet thick. These works,

which are very deep, some of them exceeding a hundred fathoms, extend under the sea. The Workington mines were carried on in a similar manner, until an irruption of the sea, in the year 1837, destroyed this valuable colliery, with much loss of life. This coal field likewise possesses six other valuable seams. From this district much coal is exported to Dublin, the Isle of Man, and a large portion of the eastern coast of Ireland.

On the northern side of the great Tyndale fault, near Hartleyburn, and on the south-western side of the Craven fault, at the base of Ingleborough, are two small coal fields, belonging to the series above the millstone grit, which have been thrown down by faults to a considerable depth below that portion of the same formation which caps the summit of the neighbouring hills. At Ingleborough the difference of level, caused by one of these faults, amounts to 3,000 feet.

II. CENTRAL COAL DISTRICT.

1.-Coal field of Ashby-de-la-Zouch.

This field is of an trregular figure, its greatest length from northwest to south-east being about ten miles, and its greatest breadth about eight. It is so much dislocated that it may be regarded as two detached basins, rather than a continuous whole. The strata have

rapid dips in various directions, and are surrounded by horizontal beds of the permian formation. They approach on the east, almost close to the slate rocks of Charnwood Forest; one of the coal seams has a thickness of from seventeen to twenty one feet, arising, very probably, from the union of several smaller seams. The estimated workable area of coal is 40,000 acres, having nine seams, with an aggregate thickness of thirty-three feet; the thickness of the coa measures being about 1,000 feet.

2.-Warwickshire Coal field.

This coal field is about sixteen miles long, extending from the village of Wyken and Sow, three miles east of Coventry, to Polesworth and Warestone, five miles east of Tamworth. Its average breadth is about three miles. The strata dip to the west-southwest; the inclination on the eastern edge of the coal field being as much as forty-five degrees, but decreasing on the western edge. The principal collieries are at Griff and Bedworth. In the former place four beds of coal are worked, the largest of which is nine feet in thickness. At Bedworth the two upper seams of the Griff colliery, which were there separated by shales, thirty-three yards thick, run together, and form one seam of the thickness of fifteen feet.

3.-South Staffordshire, or Dudley Coal field.

This field is very important, from the extensive iron works it maintains. Its entire length, from north to south, is about twenty miles; extending from Stourbridge over Cannock Chase, to Beverton, near Badgeley. The greatest breadth, between Walsall and Wolverhampton is about seven miles. Its superficies, from actual survey, is about sixty square miles. That portion of it south of Cannock Chase, eight miles long and four broad, is distinguished by the presence of a continuous bed of coal, thirty feet thick, called the "main," or "ten yard coal." It is made up of thirteen different beds, some of them lying together, others separated by thin bands, or partitions of shale. In Blomfield colliery a phenomenon takes place, analogous to the splitting of the "high main" of the Newcastle coal field by the "haworth band;" the two upper beds of the ten yard coal separate from the rest, and are distinguished by the name of the "flying reed," and the interval between them increases until it amounts to twelve fathoms; four beds of shale and ironstone being interposed. The "ten yard" coal crops out

near Bilston, and from thence extends across the southern half of the coal field.

The number of coal seams in this field are eleven, with sixtyfour beds of sandstone, clay, and shale; the total thickness of the coal seams is sixty-seven feet. At Dudley the "ten yard" coal is about sixty fathoms below the surface. None of the seams above it are there considered worth the working. The strata north of Bilston, and in Cannock Chase, are below the "ten yard" coal, and are distinguished by the presence of valuable beds of ironstone. Several of the lower seams are of considerable thickness. The ironstone measures, emerging from beneath the main coal at the southern end of the district, occupy the tract between Halesowen and Stourbridge, containing the celebrated fire-clay.

Of the great mass of coal contained in the ten yard bed, it is calculated that one-third is left in the works as refuse; the pillars, that support the roof, occupy one-third, so that not much more than one-third is actually brought to the surface.

The carboniferous limestone, and the old red sandstone formations, are entirely wanting beneath this coal field, though traces of the former may be observed in the neighbouring districts of Colebrookdale, and the Clee Hills. This circumstance is considered, by Sir Roderick Murchison, as indicating the accumulation of the coal strata at Dudley, in a fresh water lake. These coal strata rest unconformably along the base of the Silurian limestones.

Many dykes and faults, chiefly filled with sand and clay, traverse this district, and thus cause great variations in the same beds, in the different parts of their course.

The extension of the coal measures beneath the new red sandstone, has been proved by the Earl of Dartmouth, who, after sinking one hundred and fifty yards through that rock, reached the coal seams which overlie the ten-yard coal. This experiment was made at Christ Church, about a mile beyond the superficial boundary of the coal field.

"In a colliery, near Wolverhampton," says the late Hugh Miller, "the bottom coal rises to view, and when the surface has been cleared of its alluvial covering, it presents the appearance of a moor on which a full-grown fir wood had been cut down a few months before, and only left the stumps behind; stump rises behind stump, to the number of seventy-three in all, the thickly clinging roots strike out on every side into what seems to have been a vegetable

mould, but now exists as an indurated shale. Many trunks, sorely flattened, lie recumbent on the coal; several are full thirty feet in length, while some of the larger stumps measure rather more than two feet in diameter. There lie, thick around, Stigmariæ, Lepidodendra, Calamites, and fragments of Ulodendra, and yet, with all the assistance which these lent, the seam of coal, formed by this ancient forest, does not exceed five inches in thickness. Not a few of the stumps in this area are evidently water-worn. The prostrate forest has been submerged, and molluscs lived, and fishes swam over it. This upper forest is underlaid by a second, and even a third; we find three full grown forests, closely packed up in a depth of not more than twelve feet.”**

III.-WESTERN COAL DISTRICT.

1.-Coal field of North Wales.

This coal field forms a narrow belt between the slate mountains of the Cambrian chain and the sea, commencing at the western cape of the estuary of the Dee, and extending to a point a little north of Wrexham; south of which two detached tracts appear at Chirk and Oswestry; the first three, and the second about five miles long, with a breath of about half a mile. The beds of the Flintshire coal field dip beneath the Dee, at angles varying from 12° to 35°, and rise on the opposite side of the estuary; they then run under a covering of new red sandstone to join the Lancashire coal field. The mountain limestone forms the base of these measures, succeeded by beds of shales, gritstones, and chert, above which are the coal measures proper. The main seam of coal is about eight or nine feet in thickness, and the other seams vary from two to four, and six feet; some of those near the surface have been much worked. At Bagillt three seams are worked, the thickest of which is seven feet, and the thinnest, three feet. Coal is also worked at two places in the Isle of Anglesey, in the depression parallel to the Menai Straits, which extends from Red Wharf bay to the Malltraeth estuary; but it is doubtful whether this coal field belongs to the series above the millstone grit, or is subordinate to the carboniferous limestone.

2.-Coal field of Colebrookdale.

This coal field is bounded on the east by an undulated line, ranging by Lilleshall to Bridgenorth, on the north-west, by a line

* Hugh Miller's "First Impressions," &c., page 223.