of the globe is still unknown; but it appears from those parts with which we are acquainted, that coal is found principally in temperate regions, between thirty five and sixty five degrees of latitude. In Europe, Great Britain, France, Flanders, and Germany, (particularly Silesia, Saxony, Bohemia, and Thuringia,) contain large coal formations; but in the southern and more northern parts of Europe, coal is of rare occurrence. In North America, coal is found in great abundance on the western side of the Alleghany mountains; it has also been discovered in Pennsylvania, extending westward towards Pittsburgh, over a space of three hundred miles. Coal occurs also near Richmond, in Virginia, and in Missouri. American coal* is said to be found in quartz rock, which I apprehend to be merely siliceous grit, composed of nearly pure granular silex, such as abounds in the lower part of the Yorkshire coal-fields. The coal, in a great part of the United States, contains little bitumen, and hence is called anthracite : it is not, however, the true anthracite of mineralogists, but far more valuable for fuel. The discovery of this immense repository of coal, accompanied with ironstone, must prove of the highest importance to a nation so industrious, intelligent, and enterprising, as the inhabitants of the United States. In the vicinity of Pittsburgh, I am informed, that the strata of coal are nearly horizontal, and that in one situation, the same stratum of coal forms the bed of a river for several miles. Coal has been discovered in New Holland. The only great coal formations in Asia that we know of, are in China, where coal is described as existing in large quantities, and as being extensively used for fuel in that vast empire.

As France will probably continue to be, for many centuries, our great manufacturing rival, it is interesting to know what are her resources, for the supply of an article found so essential to almost all the principal manufactures of Great Britain. Before the late peace, forty seven of the departments contained coal districts, and the annual consumption was stated to be about five millions of tons; but a great part of the rich and extensive coal-field extending from Valenciennes to Aix-la-Chapelle, is comprised in that part of Flanders, which was separated from France at the peace. There are, however, extensive coal districts in the north-eastern, the western, the middle, and the southern parts of France. Two miles from Lyons there are coal mines; the coal of St. Etienne and the ironstone beds accompanying it, about twenty miles north-west of Lyons, are of the very best quality. In the year 1822, when I passed through that country, many English workmen were employed in the iron-works, which were rapidly increasing. It cannot be doubted, that, from its soil, its climate, and its mineral resources, France possesses every advantage which a great manufacturing nation can require.

For an account of American coal, the reader is referred to the conclusion of this volume, where will be found more full and precise statements.

OBSERVATIONS ON THE PERIOD WHEN THE COAL MINES IN

ENGLAND WILL BE EXHAUSTED.

Coal was known, and partially used, at a very early period of our history. I was informed by the late Marquis of Hastings, that stone hammers and stone tools were found in some of the old workings in his mines at Ashby Wolds; and his lordship informed me also, that similar stone tools had been discovered in the old workings in the coal mines in the north of Ireland. Hence we may infer, that these coal mines were worked at a very remote period, when the use of metallic tools was not general. The burning of coal was prohibited in London in the year 1308, by the royal proclamation of Edward the First. In the reign of Queen Elizabeth, the burning of coal was again prohibited in London during the sitting of parliament, lest the health of the knights of the shire should suffer injury during their abode in the metropolis. In the year 1643, the use of coal had become so general, and the price being then very high, many of the poor are said to have perished for want of fuel. At the present day, when the consumption of coal, in our iron furnaces and manufactories, and for domestic use, is immense, we cannot but regard the exhaustion of our coal beds as involving the destruction of a great portion of our private comfort and national prosperity. Nor is the period very remote when the coal districts, which at present supply the metropolis with fuel, will cease to yield any more. The annual quantity of coal shipped in the rivers Tyne and Wear, according to Mr. Bailey, exceeds three millions of tons. A cubic yard of coal weighs nearly one ton; and the number of tons contained in a bed of coal one square mile in extent, and one yard in thickness, is about four millions. The number and extent of all the principal coal-beds in Northumberland and Durham are known; and from these data it has been calculated, that the coal in these counties will last 360 years. Mr. Bailey, in his Survey of Durham, states, that one third of the coal being already got, the coal districts will be exhausted in 200 years. It is probable that many beds of inferior coal, which are now neglected, may in future be worked; but the consumption of coal being greatly increased since Mr. Bailey published his Survey of Durham, we may admit his calculation to be an approximation to the truth, and that the coal of Northumberland and Durham will be exhausted in a period not greatly exceeding 200 years. Dr. Thomson, in the Annals of Philosophy, has calculated that the coal of these districts, at the present rate of consumption, will last 1000 years; but his calculations are founded on data manifestly erroneous, and at a variance with his own statements; for he assumes the annual consumption of coal to be only two million eight hundred thousand tons, and the waste to be one third more,-making three million seven hundred thousand tons, equal to as many square yards; whereas, he has just before informed us, that two million chaldrons of coal, of two tons and a quarter each chaldron, are exported, making four million five hundred thousand tons, beside inland consumption, and waste in

the working.* According to Mr. Winch, three million five hundred thousand tons of coal are consumed annually from these districts; to which if we add the waste of small coal at the pit's mouth, and the waste in the mines, it will make the total yearly destruction of coal, nearly double the quantity assigned by Dr. Thomson. Dr. Thomson has also greatly overrated the quantity of the coal in these districts, as he has calculated the extent of the principal beds from that of the lowest, which is erroneous; for many of the principal beds crop out, before they reach the western termination of the coal-fields. With due allowance for these errors, and for the quantity of coal already worked out, (which, according to Mr. Bailey, is about one third,) the 1000 years of Dr. Thomson will not greatly exceed the period assigned by Mr. Bailey for the complete exhaustion of coal in these counties, and may be stated at 350 years.

It cannot be deemed uninteresting to enquire, what are the repositories of coal that can supply the metropolis and the southern counties, when no more can be obtained from the Tyne and the Wear. The only coal-fields of any extent on the eastern side of England, between London and Durham, are those of Derbyshire, and those in the West Riding of Yorkshire. The Derbyshire coal-field is not of sufficient magnitude to supply, for any long period, more than is required for home consumption, and that of the adjacent counties. There are many valuable beds of coal in the western part of the West Riding of Yorkshire which are yet unwrought; but the time is not very distant when they must be put in requisition, to supply the vast demand of that populous manufacturing county, which at present consumes nearly all the produce of its own coal mines. In the midland counties, Staffordshire possesses the nearest coal district to the metropolis, of any great extent; but such is the immense daily consumption of coal in the iron furnaces and founderies, that it is generally believed, this will be the first of our own coal-fields that will be exhausted. The thirty-feet bed of coal in Dudley coal-field is of limited extent; and in the present mode of working it, more than two thirds of the coal is wasted and left in the mine.

If we look to Whitehaven or Lancashire, or to any of the minor coal-fields in the west of England, we can derive little hope of their being able to supply London and the southern counties with coal, after the import of coal fails from Northumberland and Durham. We may thus anticipate a period not very remote, when all the English mines of coal and ironstone will be exhausted: and were we disposed to indulge in gloomy forebodings, like the ingenious authoress of the "Last Man," we might draw a melancholy picture of our starving and declining population, and describe some manufacturing patriarch,

* The waste of coal at the pit's mouth may be stated at one sixth of the quantity sold, and that in the mines at one third. Mr. Holmes, in his Treatise on Coal Mines, states the waste of small coal at the pit's mouth to be one fourth of the whole.

like the late venrable Richard Reynolds, travelling to see the last expiring English furnace, before he emigrated to distant regions.

Fortunately, however, we have in South Wales, adjoining the Bristol Channel, an almost exhaustless supply of coal and ironstone, which are yet nearly unwrought. It has been stated in the present chapter, that this coal-field extends over about twelve hundred square miles, and that there are twenty three beds of workable coal, the total average thickness of which is 95 feet, and the quantity contained in each acre is 100,000 tons, or 65,000,000 tons per square mile. If from this we deduct one half for waste, and for the minor extent of the upper beds, we shall have a clear supply of coal, equal to 32,000,000 tons per square mile. Now, if we admit that the five millions of tons of coal from the Northumberland and Durham mines is equal to nearly one third of the total consumption of coal in England, each square mile of the Welsh coal-field would yield coal for two years' consumption; and as there are from one thousand to twelve hundred square miles in this coal-field, it would supply England with fuel for two thousand years, after all our English coal mines are worked out.

It is true, that a considerable part of the coal in South Wales is of an inferior quality, and is not at present burned for domestic use; but in proportion as coal becomes scarce, improved methods of burning it will assuredly be discovered, to prevent any sulphurous fumes from entering apartments, and also to economize the consumption of fuel in all our manufacturing processes.

N. B. These observations are taken from one of the author's geological lectures, which he has occasionally delivered in some of the principal mining districts in England: considering the great national importance of our coal mines, he trusts he shall be excused for inserting them in the present volume.

* The late Richard Reynolds, Esq. of Bristol, so distinguished for his unbounded benevolence, was the original proprietor of the great iron-works in Colebrook Dale, Shropshire. Owing, I believe, partly to the exhaustion of the best workable beds of coal and ironstone, and partly to the superior advantages possessed by the iron-founders in South Wales, the works at Colebrook Dale were finally relinquished, a short time before the death of Mr. Reynolds. With a natural attachment to the scenes where he had passed his early years, and to the pursuits by which he had honorably acquired his great wealth, he travelled from Bristol into Shropshire, to be present when the last of his furnaces was extinguished, in a valley where they had been continually burning, for more than half a century.

CHAPTER IX.

ON UNCONFORMABLE TRAP ROCKS AND BASALTIC DYKES.

Different Positions of Trap Rocks, as overlying, imbedded in, or intersecting other Rocks. Varieties of Trap Rocks.-Porphyry, Porphyritic Trap, Sienite, Greenstone, Clinkstone, Basalt, Amygdaloid, and Wacke.-Passage by Gradation into each other, and into Volcanic and Granitic Rocks.-Remarkable Instance of this Passage at Christiania in Norway.-Mountains of Porphyritic Trap and Clinkstone with deep Craters.-High Stile, Cumberland, Cader Idris, Monmouthshire.-Basaltic Dykes: Extent of the Cleveland Basalt Dyke.-Isolated Caps of Basalt.-On interstratified Basalt.-Remarks of Professor Sedgwick on the Protrusion of Basalt between regular Strata.-On columnar Ranges of Basalt.-Organic Remains enveloped in Basalt.-Remarkable Basaltic Districts in Europe and America.-Experiments on Basalt.-Theory of Werner. On the relative Age of Trap Rocks.

The class of rocks about to be described in the present chapter, are extremely interesting to the geologist, as they present him with decided indications of their origin and mode of formation. They not only "reveal the secret of their birth," but, from their close alliance to many of the most ancient primary rocks, they disclose the operations by which a large portion of the earth's surface was consolidated, in the most remote geological epochs. Many of the trap rocks are so similar in structure and composition to the products of active volcanoes, and to beds of lava erupted in our own times, that we may be said to see the very cause in operation, by which they were formed. Many of the trap rocks are also so similar in structure and composition to some of the most ancient primary rocks, that we can scarcely doubt respecting their having had the same origin, though they may have been consolidated under different degrees of heat or pressure, and with different attendant conditions. The name Trap is derived from the Swedish word trappa, a stair, and has been given to rocks, of this class, because many of them divide into regular forms resembling the steps of stairs. Whether the term, in its literal sense, is well chosen as a generic name, may be doubted; but, taken metaphorically, it is extremely appropriate, as these rocks offer a series of gradations or steps, over which the geologist may safely travel in his speculations, from the lava of Etna, to the granite of the Alps.

To obtain a correct knowledge of trap rocks, the student should first acquire a clear idea of their position. When primary and transition rocks form distinct beds, they are generally arranged conformably, or, in other words, the upper beds are moulded upon the lower, and have the same elevations and depressions, as represented Plate III. fig. 1.