And then came another geographical revolution, some twenty million years ago, that raised up the Rockies and the Andes along the western border of the Americas, tore and twisted and upturned the rocks of Europe and Asia, until with the exception of a few odd pockets where small swamp forests lived on for a time, the coal making of the whole earth was ended. Twenty million years ago, all the coal we have or shall have had been packed away beneath the ribs of the earth, in seams varying in height from sixty feet to the thickness of a blade of grass. In many places the flat layers in which it was first deposited had been thrown into overlapping folds. Some of it had been subjected to comparatively little heat and to the pressure only of the rocky strata above it; this is the bituminous, which is still rich in oils, gas, tar--unreleased volatile matter. Some had been crushed by the weight of uplifted mountains, roasted, fused, and burned by molten lava and volcanic flame; this is anthracite, which is almost pure carbon and ash. Some had been exposed to greater pressure still, to intenser heat; this is graphite, which can no longer be burned at all. The distribution of coal in the world by quality and quantity has been, next to climate and the fertility of the soil, the physical fact of most decisive importance in the history of modern civilization. For countless ages coal lay practically unused in the earth. Then, sometime between 1750 and 1760, an intricate interlocking of circumstances set coal to rule the world, not through new discoveries of coal itself but rather through improvements in spinning and weaving machinery which made possible the massing of large numbers of spinners and weavers for large-scale production if power could be found to drive the new machines for them. The steam engine had already been invented, but it was still a tentative thing, a primitive type, wondered at and experimented with. Coal had been used, but only in a few favored spots where it cropped out on the earth's surface, or was washed ashore by the sea, and then only as a domestic fuel. It was at the call of the master weavers and spinners of England that the steam engine was set to run the machines; then to furnish a blast so that coal might be used to cheapen the smelting of iron and steel so that more machines might be made; then to pump out the deepening mines so that more and more power to keep the machines running might be won. Steam raising was coal's first great play for power and it is the work through which it still holds its industrial supremacy. Between 1800 and 1900 coal-driven engines multiplied until by the end of the century they were producing energy equivalent to seventy million horse-power; during the first twenty years of the twentieth century, their power-producing capacity more than doubled. So coal wrought the industrial revolution, the greatest revolution in all human history, which transformed social and economic life as radically as the