It appears from the researches of modern chemistry that the different varieties of coal are due to the progress of decomposition which wood and vegetable matter undergo when buried in the earth, exposed to moisture, and partially or entirely excluded from the air. Slowly evolving carbonic acid gas, and thus parting with a portion of their original oxygen, they become gradually converted into lignite or wood- coal, which contains a larger proportion of hydrogen than wood does. A continuance of decomposition changes this lignite into common or bituminous coal, chiefly by the discharge of carburetted hydrogen, or the gas by which we illuminate our streets and houses; and bituminous coal still continuing to evolve its volatile matter, not only after its being covered with strata thousands of feet in thickness, but even to the present day (as the fire-damp sufficiently proves) is thus ultimately transformed into anthracite, to which the various names of splint-coal, glance-coal, hard-coal, and culm have been given. When we consider the manner in which coal has been formed in swampy lowlands, or more particularly in river-deltas, which gradually subsided to a considerable depth beneath the level of the sea, we cannot wonder that, when compared with the whole extent of the globe, the area of the coal-fields is extremely limited, and confined to but a few favoured countries. In our times delta lands occupy but a small part of the continents and large islands, and there is no reason to suppose that they were more considerable during the carboniferous age, or at any other epoch. Besides, many of the ancient deltas, probably, never subsided at all, so that no coal could be formed on their site; and others, where coal strata were gradually piled up, may still be whelmed beneath the sea awaiting some future upheaval to become serviceable to future generations of man. After the preliminary remarks on coal and the coal formation in general, I will now briefly describe the chief coal-producing countries of the globe. First on the list stands Great Britain, whose pre-eminence in industry and commerce is entirely founded on her vast deposits of coal. It is this invaluable mineral which sets those countless steam-engines in motion that perform the labours of a hundred millions of men; which spins and weaves the cotton of America, the silk of China, the wool of Australia, and the flax of Belgium into that amazing variety of tissues that serve to clothe almost all the nations of the globe; and which finally produces a greater quantity of the cheapest iron than the combined efforts of all the world. Thus our coals may well be called our black diamonds, and the comparison is indeed paying the latter too high a compliment, for larger masses of diamonds would be utterly worthless, while, by means of our coal, we are able to enjoy the produce of every zone.