So vast a consumption leads naturally to the inquiry, "What, at this rate of annual excavation, will be the probable duration of this coal-field?" This question occupied a great deal of the attention of the committees of both houses of Parliament, already spoken of, and there was a very wide difference in the answers which they received. Mr. Taylor was asked by the lords' committee, if he had formed any calculation of the extent, produce, and duration, of the Durham and Northumberland coal-fields; and he replied that he had endeavored to do so, and gave in the following statement, which he said, however, was only to be considered as an approximation:—

He estimates the Durham coal-field south of the Tyne to embrace an area of

The Northumberland coal-field

594 square
243

66

Amounting to

And he considers that of this there had been excavated

miles.

Then estimating the workable coal strata at an average thickness of 12 feet, the contents of one square mile will be 12,390,000 tons, and of 732 square miles

And deducting one third part for loss in working, and from disturbances in the strata

There remain

- 9,069,480,000 tons.

3,073,160,000 66

- 6,046,320,000 66

This very comfortable and consolatory view of the present race, and of that of a far distant posterity, as regards this valuable commodity, is, however, a good deal disturbed by the opinions of Dr. Buckland and Mr. Sedgwick, the professors of geology at Oxford and Cambridge. Dr. Buckland being asked whether he considered the estimate of Mr. Taylor correct, answered that he thought it much exaggerated. Mr. Sedgwick is also of opinion that Mr. Taylor's estimate is too great; and both professors state the same reasons for differing so widely from the views of Mr. Taylor. He has assumed that there is a continuous thickness of twelve feet of workable coal over the whole area of seven hundred and thirty-two square miles; but all experience, both of this coal-field and of every other, is unfavorable to this assumption, for not only are the coal seams extremely variable in thickness, but they are equally so in quality, as we have already shown. The opinions of the learned professors are confirmed by another scientific observer, Mr. Bakewell, who, in his "Introduction to Geology," discusses this question, and calculates that the coal-fields now under consideration will not last above three hundred and sixty years. All these calculations, however, have reference only to the best qualities of coal-to those which can be raised at an expense sufficiently low to enable them to be sold at a remunerating price, in competition with other coals.

It appears to be very clearly made out, that all those parts of the country which are now supplied with fuel from the Northumberland and Durham mines will continue to enjoy that advantage for the next four hundred years; and those who are not so selfish and unpatriotic as to be indifferent to the fate of their posterity after the year 2,233, will learn with satisfaction that, as far as England's prosperity is connected with an abundant supply of coal, there is no danger of its sustaining any check for a much more extended period, as there is a store in reserve far greater than there was in the whole of the north-of-England field before a single fire was lighted by its produce. This extensive repository is in the coal-field of South Wales.

The geographical position of this vast deposite of the coal measures will be seen by the map on page 28. It lies in a great basin of the carboniferous limestone, which rises from under the coal strata nearly all around the limit of the coal-field. In a part of Pembrokeshire the limestone is wanting, and the coal strata rest upon slate, which is inferior to the limestone, and near Narbeth they are in contact with the old red sandstone, which lies between the slate and the limestone. In a part of the southern boundary, in Glamorganshire, the coal measures are separated from the limestone by a detached deposite of strata of posterior formation to them, and therefore lying upon them, viz., new red sandstone and lias limestone.

The coal measures do not lie horizontally within this limestone basin, but in a trough shape, being deepest toward the middle, and rising up toward the outer limits, the ends of the several strata cropping out, as the miners term it, that is, appearing successively at the surface. They do not, however, form of one uniform sweep or inverted arch; for there has been a partial up-heaving of the strata, so that a section across the field from Bridgend, due north, would present the following appearance:—

N

S

There are thus two basins, the one lying to the north, the other to the south of a high ridge, a, which runs from Aberavon, half a mile north of the Avon, by Cefn Eglwysillan, two or three miles north of Caerphilly, a little beyond which it disappears. In the northern basin, which is by far the most extensive, the strata are much less inclined than in the southern basin; for in the former the dip of the strata is generally under ten degrees, while in the latter it is often forty-five degrees, and upward. The whole coal-field is traversed by dikes or faults, generally in a north and south direction, which throw all the strata from three hundred to six hundred feet up or down. The nature of these faults we have heretofore explained. On the western termination of the basin, in St. Bride's bay, the strata exhibit the most extraordinary marks of confusion and derangement, being vertical and twisted in every possible di

rection.

The extent of this coal-field, and the thickness of the seams, have been variously stated by different authors; but the estimate which is perhaps the most to be relied upon, is that of the Rev. William Conybeare, the eminent geologist, who has long resided in the country, and is perfectly familiar with its geology. It is contained in a letter addressed by him to Henry Warburton, Esq., M. P., published in the report of the committee of the house of commons, already referred to. Mr. Conybeare makes three great divisions of the coal seams-the lower, middle, and upper series; and he assigns to them, respectively, the average thickness of thirty-five, fifteen, and ten feet, making altogether sixty feet of workable coal. Martin, who described this coal-field, makes them amount to ninety-five feet; and Mr. Conybeare thinks that Martin does not overstate the amount, provided all the seams be taken into the account. But Mr. Conybeare's calculation only includes the workable coals, and he considers that those seams can not be worked with profit where it is necessary to go lower than two hundred fathoms, or twelve hundred feet, for beyond this the expense of drainage, &c., becomes enormous. Keeping the same considerations in view, Mr. Conybeare makes the following estimate of the area occupied by the coal-seams:

This, it is calculated, after deducting one half for loss and for what has been already worked, will amount to about eleven billions four hundred and twenty-three millions seven hundred and fifty thousand tons; and taking the annual consumption of all England at fifteen millions of tons, the provision of good coal in the South Wales basin is sufficient for seven hundred and sixty years. Taking all that remains in the Northumberland and Durham coal-fields, and all the other coal-fields of England together at three times that amount, and which we are inclined to think would not be an over-estimate, we have a supply of good coal, which, at the present rate of consumption, would last above three thousand years. How long beyond that time the inferior seams will yield a supply of fuel, we shall leave posterity to calculate.

To the east of the line drawn from Exmouth to Bath, and thence by Gloucester, Leicester, and Tadcaster, to Stockton-upon-Tees, we find the upper rocks of the secondary formation, presenting in succession red sandstone and red marl, lias limestone and clay, oolitic limestone, green sand with clay, and finally chalk. Connected with the red marl, great strata of rock-salt are found; these are extensively dug in Cheshire and Worcestershire for domestic use.

The limestone, like the granite, frequently assumes very singular forms and appearances, and has sometimes been named from its similarity to works of art. This is the case with the Matlock high tor of Derbyshire, an engraving of which is presented in the next page.

The word tor is a Saxon one, from whence, according to the etymologists, comes our word tower. The Latin turris, the Saxon tor, and the English tower, appear to be related in their signification; meaning, in their original sense, something erected on an eminence. We find preserved the syllable tor, as we find many other words which are of what are termed Cimbro-Celtic and Teutonic or Gothic origin, in the names of many places of Britain.

Matlock is well known as a summer resort of invalids and idlers, as well as of those who go, for recreation or information, to see the wonders of the peak of Derbyshire-the rocks, mines, and caverns, and other mountainous scenery of that truly singular and interesting region. "Matlock dale,," says Mr. Jewitt, in a little work called the "Matlock companion," "is naturally a deep narrow ravine, how produced, or by what convulsion, must be left to geologists to determine. One side is formed by lofty perpendicular limestone rocks, the other by the sloping sides of giant mountains; along the bottom runs the Derwent, sometimes pent up in a narrow channel, and obstructed by the fragments which have, from time to time, fallen from the beetling tor, and sometimes spreading like a lucid lake, and reflecting as a mirror the beautiful but softened tints of the overhanging foliage."

Matlock dale, which in the time of De Foe was almost inaccessible from the want of a road, and which, still more recently, was praised as being a retired, secluded spot, now lies on the direct road from London to Manchester. This, as is well remarked by Mr. Jewitt, though destroying the previous character of the place, has brought it more into notice, and a much larger accession of visiters than it could have otherwise received.

The high tor is a huge rock, which rises almost perpendicularly from the Derwent to a height of upward of 400 feet. The lower part is covered with foliage, but the upper part presents a broad bold front of gray limestone. It forms a part of the chain of rocks which bound the river on the east, but from its superior height and boldness is one of the most remarkable of the objects of Matlock dale, and is distinguished for its effect, even in the midst of scenery all of which is celebrated for