While this development of the agricultural interests of the Middle West has been in progress, the exploitation of the pine woods of the north has furnished another contribution to the commerce of the province. The center of activity has migrated from Michigan to Minnesota, and the lumber traffic furnishes one of the principal contributions to the vessels that ply the Great Lakes and supply the tributary mills. As the white pine vanishes before the organized forces of exploitation, the remaining hard woods serve to establish factories in the former mill towns. The more fertile denuded lands of the north are now receiving settlers who repeat the old pioneer life among the stumps. But the most striking development in the industrial history of the Middle West in recent years has been due to the opening up of the iron mines of Lake Superior. Even in 1873 the Lake Superior ores furnished a quarter of the total production of American blast furnaces. The opening of the Gogebic mines in 1884, and the development of the Vermillion and Mesabi mines adjacent to the head of the lake, in the early nineties, completed the transfer of iron ore production to the Lake Superior region. Michigan, Minnesota, and Wisconsin together now produce the ore for eighty per cent of the pig iron of the United States. Four-fifths of this great product moves to the ports on Lake Erie and the rest to the manufactories at Chicago and Milwaukee. The vast steel and iron industry that centers at Pittsburgh and Cleveland, with important outposts like Chicago and Milwaukee, is the outcome of the meeting of the coal of the eastern and southern borders of the province and of Pennsylvania, with the iron ores of the north. The industry has been systematized and consolidated by a few captains of industry. Steam shovels dig the ore from many of the Mesabi mines; gravity roads carry it to the docks and to the ships, and huge hoisting and carrying devices, built especially for the traffic, unload it for the railroad and the furnace. Iron and coal mines, transportation fleets, railroad systems, and iron manufactories are concentrated in a few corporations, principally the United States Steel Corporation. The world has never seen such a consolidation of capital and so complete a systematization of economic processes. Such is the economic appearance of the Middle West a century after the pioneers left the frontier village of Pittsburgh and crossed the Ohio into the forests. De Tocqueville exclaimed, with reason, in 1833: "This gradual and continuous progress of the European race toward the Rocky Mountains has the solemnity of a providential event. It is like a deluge of men, rising unabatedly, and driven daily onward by the hand of God."