The making of all the coal in the earth began when the sun hurled the earth into its orbit. Before there were vertebrates in the sea, or animals, or plants of any kind on land--fully one hundred and fifty million years ago--low foldings and depressions appeared on the earth where the Appalachian Mountains now are. Following the lines of what has become the Atlantic, vast ridges appeared. Ages later swamp forests grew in the intervening valleys, bearing and shedding the spores and thick, somber leaves still traceable in the lower carboniferous strata. In that time, a shallow sea covered what is now the Mississippi Valley in whose sludgy shoals more swamp forests grew. Along the inland seas and ocean beaches of Europe and Asia, the tides, the winds, and rains slowly spread the clay for still other swamp forests. When the lush plant life of the carboniferous age came out of the marshy ooze, it spread along the edges of the land, crept up the long estuaries between the rising and sinking hills and on into the landlocked seas. The rocks beneath and about these carboniferous forests rose and sank age through age, cycle through cycle. When they sank slowly, tangled morasses formed; when they sank rapidly, the inrushing water killed the plants and buried them under a covering of silt. When the rocky strata rose again, the swamp forests crept back to their old places, and again bore and shed their fernlike leaves, their spores and great scarred trunks upon the oozy bottom now scores or hundreds of feet above the level on which their ancestors had stood ages before. Then, some seventy million years ago, a geographical revolution convulsed what is now northeastern America. The great trough running parallel to the Atlantic, where swamp forests had grown and died and grown again, gave way under the ever-increasing load. The ridges at its sides pressed in upon it, crumpled it into giant folds, broke it, pushed its shattered edges out in mighty over-thrusts, released molten rock to flow up and over its torn surface. The whole titanic mass was racked and twisted with pressure and heat until what had been a slowly subsiding sea-bottom, covered with decaying swamp vegetation, rose on the shoulders of the newborn Appalachian Mountains, then a lofty range of clean, stark peaks stretching from Newfoundland to Arkansas,--two thousand miles. And with this great geographical revolution, the work of making coal in eastern North America was finished. From the softest bituminous to the hardest anthracite, that work was done. But in other parts of the world, the dense carboniferous forests continued to grow for another fifty or more million years. In the shallows of the Mississippi Valley, on the shores of the island that is now Colorado, the coal plants grew and died with the seasonal march of the sun. In parts of Europe, Russia, and China, coal continued to form.