The use of C. does not seem to have been known to the ancients; nor is it well known at what time it began to be used for fuel. Some say that it was used by the ancient Britons; and at all events it was to some extent an article of household con sumption during the Anglo-Saxon period as early as 852 A.D. There seems to be reason fog thinking that England was the first European country in which C. was used to any considerable extent. About the end of the 13th c., it began to be employed in London, but at first only in the arts and manufactures; and the innovation was complained of as injurious to human health. In 1316, the parliament petitioned the king, Edward II., to prohibit the use of C., and a proclamation was accordingly issued against it; but owing to the high price of wood, its use soon became general in London. It was for a long time known there as sea C., because imported by sea.
Several theories as to the mode of the origin of C. have been put forth from time to time. The one now generally believed in is that the rank and luxuriant vegetation which prevailed during the carboniferous age grew and decayed upon land but slightly raised above the sea; that by slow subsidence this thick layer of vegetable matter sunk below the water, and became gradually covered with sand, mud, and other mineral sedi ment; that then, by some slight upheaval of the sea bottom or other process, a land surface was once more formed, and covered with a dense mass of plants, which in course of time decayed, sank, and became overlaid with silt and sand as before. At length, thick masses of stratified matter would accumulate, producing great pressure, and this, acting along with chemical changes, would gradually mineralize,the vegetable layers into coal. Some experiments made by Dr. Lindley, a few years ago, showed that of a large number of plants kept immersed in water for two years, the ferns, lycopodiums, and pines were those which had the greatest powers of resisting decay, and C. appears to be mainly composed of the substance of the ancient representatives of these three orders of plants. The interesting fact has also been lately proved by Huxley, Morris, Car ruthers, and others, that in many instances the bituminous matter in C. is almost wholly formed of the spore cases and spores of plants allied to our club-mosses and ferns.
As will be seen from the following table, wood, peat, lignite or brown C. and true C. indicate by their composition the changes which vegetable matter undergoes by decay and pressure; and a table in which a considerable number of examples of each substance could be given would show how gradually these substances pass into each other: In each of these bodies. there is usually a small percentage of nitrogen, which in the above table has not been separated. In passing from wood or peat to C., the proportion of oxygen and hydrogen decreases, these substances being given off in the form of marsh-gas and carbonic acid in the process of decay.
Since the prosperity of our great national industries, as well as much of our domestic comfort, depends on the continuance of an abundant supply of cheap fuel, much anxiety has arisen in Great Britain of late years regarding the future supply and price of coal. Since the fall of 1872, a great rise has taken place in its price. This is partly owing to the unusually hi4h rate of miners' wages which has prevailed, and partly to the fact that some of the richest and most easily worked English coal-seams are becom ing exhausted. There is therefore some cause for apprehension, yet, as the following figures taken from the estimate in the report of the royal commission on C., dated 1871, will show, we have still vast supplies of fossil fuel.
Taking into account the coal which probably exists under the permian, new red sandstone, and other superincumbent strata in the United Kingdom, the C. commis sioners increase their estimate of the quantity still available for use to 146,480 millions of tons. At the present rate of annual production—namely, 123,500,000 tons, this would last 1186 years. But, as may be supposed, the estimates which have been put forth regarding the probable duration of our coal-fields are very various, some authorities asserting that, owing to increase in population, and the increasing consumption of coal in manufactures, about 100 years will suffice to exhaust them. Between this and the other extreme of about 1000 years, formed on the assumption that hereafter the popula tion of the country will but slightly increase, there are innumerable conjectures and estimates.
On the continent of Europe, productive coal-fields occur in Belgium, France, vari ous parts of northern Germany, Spain, and Russia. By far the largest in area are those of Russia, and they are known to contain many valuable beds of C., although, as yet, comparatively little has been worked. C. is also found in India, China (where the coal fields are estimated to cover 400,000 sq.m.), Japan, and the Malayan archipelago, in Australia and New Zealand, and in Africa. Turning to the new world, there is evi dence of promising coal-deposits in several South American countries, but, owing to the great supply of wood in their forests, there is little temptation to work them. In Can ada, Nova Scotia, New Brunswick, and Newfoundland, there are small though able coal-fields; but, in the United States, enormous fields of fossil fuel are found. The entire area of these is about 200,000 sq.m., being 38 times greater than the area of the coal-fields of Great Britain. But although the coal-measures of the states are of vast extent, and contain many valuable coal-seams—a few of them 40 and even 50 ft. thick at certain places—it has been doubted whether the amount of workable C. in them is not greatly exaggerated by American writers. In proportion to the extent of the seams, the quantity of C. annually raised in the states is small, being only about 40,000,000 tons.