"All sediments deposited in the sea," says my geology, "undergo more or less chemical change," and many chemical changes involve notable changes in volume of the mineral matter concerned. It has been estimated that the conversion of granite rock into soil increases its volume eighty-eight per cent, largely as the result of hydration, or the taking up of water in the chemical union. The processes of oxidation and carbonation are also expansive processes. Whether any of this gain in volume is lost in the process of sedimentation and reconsolidation, I do not know. Probably all the elements that water takes from the rocks by solution, it returns to them when the disintegrated parts, in the form of sediment in the sea, is again converted into strata. It is in this cycle of rock disintegration and rock re-formation that the processes of life go on. Without the decay of the rock there could be no life on the land. Water and air are always the go-betweens of the organic and inorganic. After the rains have depleted the rocks of their soluble parts and carried them to the sea, they come back and aid vegetable life to unlock and appropriate other soluble parts, and thus build up the vegetable and, indirectly, the animal world. That the growth of the continents owes much to the denudation of the sea-bottom, brought about by the tides and the ocean-currents, which were probably much more powerful in early than in late geologic times, and to submarine mineral springs and volcanic eruptions of ashes and mud, admits of little doubt. That it owes much to extra-terrestrial sources--to meteorites and meteoric dust--also admits of little doubt.