To English trade the canal opened up the richest of all markets, the market of England itself. Every part of the country was practically thrown open to the manufacturer: and the impulse which was given by this facility of carriage was at once felt in a vast developement of production. But such a developement would have been impossible had not the discovery of this new mode of distribution been accompanied by the discovery of a new productive force. In the coal which lay beneath her soil England possessed a store of force which had hitherto remained almost useless. But its effects were now to make themselves felt. The first instance of the power of coal was shown in utilizing the stores of iron which had lain side by side with it in the northern counties, but which had lain there unworked through the scarcity of wood, which was looked upon as the only fuel by which it could be smelted. In the middle of the eighteenth century a process for smelting iron with coal turned out to be effective; and the whole aspect of the iron-trade was at once revolutionized. In fifty years the annual production of iron in Great Britain rose from under twenty thousand to more than one hundred and seventy thousand tons. During the fifty years that followed it rose to six millions of tons. Iron was to become the working material of the modern world; and it is its production of iron which more than all else has placed England at the head of industrial Europe. But iron was not the only metal which coal drew from the soil to swell the national wealth. The increase in its production was rivalled by that of lead, copper, and tin; and the "mining districts" soon gathered a population which raised them into social as well as economical importance. [Sidenote: The Steam Engine.]