We have already pointed out that earthquakes frequently happen in mountainous regions; and this fact alone suggests that perhaps the same causes which upheave mountains may have something to do with earthquakes. But there are other reasons for believing that the same force which causes earthquakes also upheaves mountain-chains. The reader will remember the case of the Chilian earthquake that raised part of the Andes a few feet in height. Now, it is quite clear that the rocks of which mountains are composed have suffered a great deal of disturbance. We have only to look at the crumbled and contorted strata to see that they have been forced into all kinds of positions, sometimes standing bolt upright (see diagrams, chap. ix., p. 307). And as we cannot believe, for many reasons, that these movements were of a very sudden or violent kind, we must consider that they took place slowly on the whole; but besides being folded and twisted, the rocks of mountains frequently exhibit clear signs of having been split and cracked. The fractures are of all sizes, from an inch or more up to hundreds or even thousands of feet. They tell us plainly that the rocks were once slowly bent, and that after a certain amount of bending had taken place, the strain put upon them became greater than they could bear, and consequently they snapped and split along certain lines. This is just what might be expected. For instance, ice on a pond will bend a good deal, but only up to a certain amount; after that, it cracks in long lines with a remarkably sharp and smooth fracture. But suppose the pressure came from below instead of from above, as when a number of people are skating on a pond. Should we not see the ice forced up in some places, so that some sheets stood up above the others after sliding past their broken edges? This is just what the rocks in different places have frequently done. After a fracture has taken place the rock on one side has slid up over the other, and the two surfaces made by the fracture--like two long walls--are no longer seen at the same level. One has been pushed up, while the other has gone down (see diagram of the ranges of the Great Basin, chap. viii., p. 273). Now, it is almost impossible to conceive of these tremendous fractures taking place in the rocks below our feet without causing sudden jars or shocks. Here, then, we seem to have a clue to the problem. Even if the movements took place only a few inches or a few feet at a time, that does not spoil our theory, but rather favours it; for in that case the upheaval of a mountain-chain will have taken a very long time (which is almost certain), and may have been accomplished bit by bit. Hundreds and thousands of earthquake shocks, some slight, and others severe, may have attended the upheaval of a mountain-range.