The earth cools and contracts with almost infinite slowness, and the great crustal changes that take place go on, for the most part, so quietly and gently that we should not suspect them were we present on the spot, and long generations would not suspect them. Elevations have taken place across the beds of rivers without deflecting the course of the river; the process was so slow that the river sawed down through the rock as fast as it came up. Nearly all the great cosmic and terrestrial changes and revolutions are veiled from us by this immeasurable lapse of time. Any prediction about the permanence of the land as we know it, or as the race has known it, or of our immunity from earthquakes or volcanic eruptions, or of a change of climate, or of any cosmic catastrophe, based on human experience, is vain and worthless. What is or has been in man's time is no criterion as to what will be in God's time. The periods of great upheaval and deformation in the earth's crust appear to be separated by millions of years. Away back in pre-Cambrian times, there appear to have been immense periods during which the peace and repose of the globe were as profound as in our own time. Then at the end of Palaeozoic time--how many millions of years is only conjectural--the truce of aeons was broken, and the dogs of war let loose; it was a period of revolution which resulted in the making of one of our greatest mountain-systems, the Appalachian, and in an unprecedented extinction of species. Later eras have witnessed similar revolutions. Why may they not come again? The shrinking of the cooling globe must still go on, and this shrinking must give rise to surface disturbances and dislocations, maybe in the uplift of new mountain-ranges from the sea-bottom, now undreamed of, and in volcanic eruptions as great as any in the past. Such a shrinkage and eruption made the Hawaiian Islands, probably in Tertiary times; such a shrinkage may make other islands and other continents before another period of equal time has elapsed.