But, the reader will naturally inquire, if "faults" gave rise to earthquakes, and faults are the result of pressure, what produces the pressure? And what produces the mountains? Before we answer that we must again have recourse to examples taken from common experience. A sheet of glass or of marble we usually regard as a thing that may break but does not bend. But all of us have seen glass strips, if they are long enough, bend under their own weight; and there are even marble mantelpieces which, if examined, show that the slab of marble has _bent_. Thus we can readily imagine that sometimes the strata of the earth will bend by reason of the weight put upon them. If that weight is not put on them quite evenly the strata will be still more likely to bend; it will go from bending to buckling, and from buckling to breaking. As soon as it breaks there will be a "fault" formed. Those who recollect what we have said about the enormous weight of the rocks one above the other will not have to search far for the cause of weight sufficient to bend or buckle the rock strata of the earth. And those who have followed carefully all that has been written about the shifting of materials from the land to the sea by the processes of denudation and erosion set up by rain and wind and carried out by streams and rivers, will easily discover where and how the shifting of great weights of the earth's surface goes on. Little by little great weights are taken from one place on the earth's surface to another, as we might shift the weights in balanced scale-pans grain by grain, till at last the heavier scale-pan goes down quickly, or it may be with a crash, and the "fault" occurs, while the earthquake follows.