The first impression which is produced upon the mind, when the phenomena of volcanic action are studied, is that here we have exhibitions of destructive violence the effects of which must be entirely mischievous and disastrous to the living beings occupying the earth's surface. A little consideration will convince us, however, that the grand and terrible character of the displays of volcanic energy have given rise to exaggerated notions concerning their destructive effects. The fact that districts situated over the most powerful volcanic foci, like Java and Japan, are luxuriant in their productions, and thickly inhabited, may well lead us to pause ere we condemn volcanic action as productive only of mischief to the living beings on the earth's surface. The actual slopes of Vesuvius and Etna, and many other active volcanoes, are abundantly clothed with vineyards and forests and are thickly studded with populous villages. As a matter of fact, the actual amount of damage to life and property which is effected by volcanic eruptions is small. Usually, the inhabitants of the district have sufficient warning to enable them to escape with their lives and to carry away their most valuable possessions. And though fertile tracts are covered by loose dust and ashes, or by lava- and mud-currents, yet the sterility thus produced is generally of short duration, for by their decomposition volcanic materials give rise to the formation of the richest and most productive soils. Earthquakes, as we have already seen, are far more destructive in their effects than are volcanoes. Houses and villages, nay even entire cities, are, by vibrations of portions of the earth's crust, reduced to heaps of ruins, and famines and pestilences too frequently follow, as the consequence of the disorganisation of our social systems by these terrible catastrophes. It may well be doubted, however, whether the annual average of destruction to life and property caused by all kinds of subterranean action, exceeds that produced either by floods or by hurricanes. Yet we know that the circulation of water and air over our globe are beneficial and necessary operations, and that the mischief occasionally wrought by the moving bodies of water and air is quite insignificant compared with the good which they effect. In the same way, we shall be able to show that the subterranean energies are necessary to the continued existence of our globe as a place fitted for the habitation of living beings, and that the mischievous and destructive effects of these energies bear but a small and insignificant proportion to the beneficial results with which they must be credited. [Sidenote: LEVELLING ACTION OF DENUDING FORCES.]