“It may perhaps be objected, that, as the altitude actually increases from the coast-line toward the interior, the same rate of recession would, in time, involve a greater loss in volume. Is this objection well founded? No; for the tendency of the rain and water-courses being, as we have said, to lower the surface-level, this action would keep pace with that of the sea. “Again, the area of the dry land being 145,000,000 square kilometers, a circle of equal area would have a radius of 6800 kilometers. But the circumference of this circle would be only 40,000 kilometers; that is to say, the sea could exercise upon the circle but one-fifth the erosive action which it actually does upon the indented outline of our shores. We may, therefore, admit that the erosive action of the sea upon the dry land is _five times greater_ than it would be upon an equivalent circular area. Certainly this estimate is a maximum; for it is logical to suppose that, when the narrow peninsulas have been eaten away by the sea, the ratio of the perimeter to the surface will decrease more and more—that is, the action of the sea will be less effective. In any event, since, at the rate of three centimeters per year, a radius of 6800 kilometers would disappear in 226,600,000 years, one-fifth of this interval, or about 45,000,000 years, would represent the minimum time necessary for the destruction of the land by the sea; this would correspond to an intensity of action scarcely more than _one-fifth_ that of the rivers and rain. “Taken together, these mechanical causes would, therefore, involve every year a loss in volume of twelve cubic kilometers, which, for a total of 100,000,000, would bring about the complete submergence of the dry land in a little more than _8,000,000 years_. [Illustration: THE NILE. ] “But we are far from having exhausted our analysis of the phenomena in question. Water is not only a mechanical agent; it is also a powerful dissolvent, far more powerful than we might suppose, because of the large amount of carbonic acid which it absorbs either from the atmosphere or from the decomposed organic matter of the soil. All subterranean waters become charged with substances which it has thus chemically abstracted from the minerals of the rocks through which it percolates. “River water contains, per cubic kilometer, about 182 tons of matter in solution. The rivers of the world bring yearly to the sea, nearly _five cubic kilometers_ of such matter. The annual loss to the dry land, therefore, from these various causes, is _seventeen_ instead of twelve cubic kilometers; so that the total of 100,000,000 would disappear, not in eight, but in _a little less than six million years_. “This figure must be still further modified. For we must not forget that the sediment thus brought to the sea and displacing a certain amount of water, will cause a rise of the sea-level, accelerating by just so much the levelling process due to the wearing away of the continents.