The immense swamps and low forest-clad plains which occupied the continental areas of the Northern Hemisphere, and which we now know extended also into the regions south of the equator, appear at the close of the Carboniferous age to have again sunk beneath the waves, or to have relapsed into the condition of sand and gravel banks; for a great thickness of such deposits rests on the coal measures and constitutes the upper coal formation, the upper "barren measures" of the coal-miners. There is something grand in the idea of this subsidence of a world of animal and vegetable life beneath the waters. The process was very slow, so slow that at first vegetable growth and deposition of silt kept pace with it; and this is the reason of the immense series of deposits, in some places nearly 15,000 feet thick, which inclose or rest upon the coal beds; but at length it became more rapid, so that forests and their inhabitants perished, and the wild surf drifted sand and pebbles over their former abodes. So the Carboniferous world, like that of Noah, being overflowed with water, perished. But it was not a wicked world drowned for its sins, but merely an old and necessarily preliminary system, which had fully served its purpose; and, like the stubble of last year, must be turned under by the plough that it may make way for a new verdure. The plough passed over it, and the winter of the Permian came, and then the spring of a new age. The Permian and the succeeding Triassic are somewhat chilly and desolate periods of the earth's history. The one is the twilight of the Palæozoic day, the other is the dawn of the Mesozoic. Yet to the philosophical geologist no ages excel them in interest. They are times of transition, when old dynasties and races pass away and are replaced by new and vigorous successors, founding new empires and introducing new modes of life and action. Three great leading points merit our attention in entering on the Permian age. The first is the earth-movements of the period. The second is the resulting mineral characteristics of the deposits formed. The third is the aspect of the animal and vegetable life of this age in their relation more especially to those which preceded. [Illustration: DIAGRAM OF FOLDINGS OF THE CRUST IN THE PERMIAN PERIOD. (The vertical scale of heights and depressions exaggerated more then six times.) The lower figure shows a portion of folded strata in the Appalachians--after Rogers.]