long continuance over the same areas of the same external conditions. So far as we can judge of the character of the vegetation (alliance to equisetums, clubmosses, tree-ferns, swamp-pines, and the like), it by no means required a tropical temperature for their growth and accumulation, but rather a moist, equable, and genial climate, inundated riverplains and morasses, low-lying deltas and sea-swamps-and these could be brought about by the terraqueous arrangements of the earth's own surface, and without calling in the aid of anything either preternatural or abnormal. We say, "could be brought about by the terraqueous arrangements of the earth's own surface;" for it is not difficult to conceive such a position of the land-masses as to receive more heat from the sun and more warmth from oceanic currents, and such a lowness also of the terrestrial surfaces as to offer few points of condensation to aqueous vapours, and thus preserve a greater permanent amount of atmospheric moisture. This moisture would act in a twofold manner in promoting luxuriance of vegetable life-first, by affording a full and direct supply for their growth; and, second, in lessening the radiation of heat from the land-surface, and thereby greatly increasing the general temperature.* But whatever the geographical conditions, they must have continued for long ages over the same areas to permit the accumulation of such a thickness of coals and sediments and igneous eruptions as those which constitute the Carboniferous system. And these accumulations imply vast continents from which they were wasted, large rivers for their transport, extensive deltas and sea-swamps for the growth of coal-beds, frequent volcanic eruptions in or near the areas of deposit, and over the whole a gradual subsidence

*For evidence of this peculiar effect of atmospheric vapour, see Professor Tyndall's reasonings and experiments in his Heat considered as a Mode of Motion.'

to allow the depositions of bed above bed in such regular and continuous arrangement. And while all this went on the march of life was ever onward and upward. Plants unknown in the Silurian and Old Red Sandstone periods made their appearance; newer genera and species of corals, shell-fish, crustacea, and fishes thronged the waters. Reptiles, so doubtfully known (or altogether unknown), in the Old Red, now appeared in considerable variety; insects, frail and fragile as they generally are, were by no means uncommon; and all that is wanting to complete the scheme of life, as now known to us, is the presence of birds and mammals. Whether this absence of birds and mammals arises from their non-existence during the period, or from the imperfection of the geological record, it is impossible to determine; but clearly the flora and fauna are greatly in advance of those of the Old Red Sandstone, and all this is in perfect harmony with the geological doctrine of a progressive development of vitality.

As an economic repository the old coal-measures present a wide field for inquiry and description. The variety and value of their products, the skill and capital expended in obtaining them, and their obvious bearings on the industrial and social relations of a nation, are subjects, however, that lie far beyond the scope of a single sketch, and all that we can attempt is little more than a mere enumeration of the principal substances. We allude, of course, more especially to the Coal-formation of the British Islands, from which it may be safely asserted that we derive products of greater value than from all the other formations put together. From its sandstones we obtain many of our most durable and beautiful building-stones; we fabricate its fireclays into furnace-bricks, retorts, drainage-pipes, baths, and other articles of utility and ornament: from its shales we

extract alum, copperas, sulphur, and paraffin oils; its limestones are employed in architecture, agriculture, iron-smelting, bleaching, tanning, and numerous other arts, at the same time that they furnish many of our most decorative marbles, and are often found veined with ores of lead, zinc, antimony, and silver: from its ironstones we extract much of that metal without which all our implements would have been comparatively rude and inefficient, and the machinery of our factories, our steamboats, our railroads, and telegraphs impossible; while with its various coals we heat our dwellings, cook our food, light our streets and apartments, and raise that steam-power by which human industry is increased ten-thousand-fold, time and space abridged, and the different nationalities of the earth brought into more intimate union and brotherhood.

And yet, important as these substances are, they are far from having attained their limit either in the amounts annually raised or in the purposes to which they can be applied. One has only to cast his eye back on the state of our coal-fields some forty or fifty years ago, as compared with what they are now, to be at once convinced of the progress that has been made, as well as of the progress that is still attainable. At that time, fire-clay was raised only from a few open workings, and had little or no value; alum-shale was mined only at a single work; black band ironstone was rejected; bituminous shales were utterly worthless; the ordinary coals had for the most part merely a local sale (for there were no railroads), and brought less than half their present prices; cannel coal was seldom raised, and was scarcely saleable even at a fifth of its present cost (for gas-works had not then come into operation); and the whole amount of coal raised in Great Britain did not much exceed 30,000,000 tons, while now it has reached the enormous amount of 100,000,000, and is still steadily

increasing! At that time steam-power had not come into general use at our collieries, and horses, men, boys, and women toiled indiscriminately under ground and above ground. Shallow workings, open inclines, and stair pits were then the order of the day, with little profit to the employer, and a world of discomfort to the employed. Now our coal-works, though still demanding improvement (especially in ventilation, and in the employment of more highly educated overseers), are models of systematic engineering in comparison, and are year after year conducted on a more enlarged scale and on more strictly scientific principles, at the same time that they have been placed. under a humane and generous system of official surveillance.

Looking, we say, at the progress that has been made during the last forty years, at the increasing demand and pressure upon our coal-supplies, and at the general improvement in mechanical appliances that is incessantly taking place, we may rely on increased national interest in all that relates to our coal-fields, to new inventions for lessening the toil and danger incident upon mining, and to a still further utilisation of the substances that belong to the Carboniferous system, and which are now only partially employed or altogether neglected. But while we look hopefully forward to this utilisation, we cannot lose sight. of the fact that our coal-fields-we mean the British coalfields—have a limited area, and that at the present rate of consumption a time must come when every available seam will be exhausted. How far distant this time may be our best practical authorities are by no means agreed, some restricting it to 300 or 400, some to 600, and others again to 1000 years. *It is true that by more economical methods

* Those interested in the probable duration of our coal-supplies may consult Hull's 'Coal-fields of Great Britain,' the most compendious, as well as the most readable, work on the subject to which we can refer them.

of consumption the present increasing demand will be somewhat restrained; that with improved methods of working much of the mineral now left underground will be raised; and that with more skilful engineering deeper shafts may be sunk through the overlying secondary rocks. But even with all these appliances, no man of intelligence can shut his eyes to the facts that we are rapidly working out our best and most accessible coal-seams, that deeper winnings must entail greater expense, and that in less than a century hence the price of British fuel will be immensely increased. How long the supply may be sufficient to sustain the supremacy of British industry it is impossible at present to determine, but assuredly two or three hundred years hence all the more accessible portions of our coalfields will be thoroughly exhausted, and our successors will be driven either to foreign fields, to other sources of heat than coal, or to other centres of industry. No doubt the vast fields of America and Australia are scarcely broken in upon, * and science is every year discovering newer fields in other regions, and this will tend greatly to lessen the pressure on those of Great Britain; but still the results must ultimately be a change in our commercial relations, and a shifting of the theatres of manufacturing industry. Under a wide and cosmical view, however, such changes are inevitable, and we need no more disquiet ourselves about the future condition of our country than about the future distributions of the seas and continents. The rise and decline of nationalities and the phases of their commercial power

* The available coal areas of Great Britain are usually estimated at little more than 5000 square miles; those of North America alone exceed 200,000! When we add to this the unknown areas of South America, of Australia, of Japan, China, and India, to say nothing of the partially explored fields of Russia and Austria, the reader will readily perceive how immense the stores of fossil fuel laid up for the future requirements of human industry.