There are two views of it. There is the outward pressure of the regions where the sediments of rock are being laid down. There is the inward pressure towards the regions which have lost soil. Sometimes these two actions may conspire. A region where great denudation is taking place may send its waste material towards the sea, where it is deposited near the coast and not far from the highlands or mountains or plateaux which founded the soil. The shallows near the shore become a belt which is being loaded; the big mountains near by are a belt which is unloading; and thus there are two strains set up together. It is not hard to see the enormous crumpling effect which this would produce on the lower strata one or two miles beneath the surface of the sea and three or four miles below the topmost crests of the mountains. These are circumstances which may not be common; but the reader will find a quite sufficient explanation of some of the crumpling, and many of the changes in composition and appearance of the deep-sunk rocks, if he remembers the great pressure over them, and the fact that the high regions may be supposed always to have a tendency to slip towards the lowlands. CHAPTER XIII EARTHQUAKES IN GEOLOGY It is more than likely that earthquakes in the geological past were very much more violent, widespread, and frequent than they are now; and they may have had a more potent effect in overturning the rocks of the earth. Even now their effects and the circumstances which accompany them are tremendous and terrifying. When the great earthquake comes, says Major Edward Dutton in his book on _Earthquakes_, it comes quickly and is quickly gone. Its duration is generally a matter of seconds rather than of minutes, though instances have been known in which it lasted from three to four minutes. Perhaps forty-five seconds would be a fair average. The first sensation is a confused murmuring sound of a strange and even weird character. Almost simultaneously loose objects begin to tremble and clatter. Sometimes almost in an instant, sometimes more gradually, but always quickly, the sound becomes a roar, the clattering becomes a crashing. The rapid quiver grows into a rude violent shaking of increasing amplitude. Everything beneath seems beaten with rapid blows of measureless power; loose objects begin to fly about; those that are lightly hung break from their fastenings. The shaking increases in violence. The floor begins to heave and rock like a boat on the waves. Plaster ceilings fall, the walls crack, the chimneys go crashing down, everything moves, heaves, tosses. Huge waves seem to rush under the foundations as if driven by a gale. The swing now becomes longer and still more powerful. The walls crack open. A sudden lurch throws out the front wall into the street, or tears off or shakes down in rubble the whole corner of the building. Then comes a longer swaying motion, not unlike a ship at sea, but