However, there are certain facts, about this agate-making, which I can tell you; and then you may look at it in a pleasant wonder as long as you like; pleasant wonder is no loss of time.
First, then, it is not broken freely by a blow; it is slowly wrung, or ground, to pieces. You can only with extreme dimness conceive the force exerted on mountains in transitional states of movement. You have all read a little geology; and you know how coolly geologists talk of mountains being raised or depressed. They talk coolly of it, because they are accustomed to the fact; but the very universality of the fact prevents us from ever conceiving distinctly the conditions of force involved. You know I was living last year in Savoy; my house was on the back of a sloping mountain which rose gradually for two miles, behind it; and then fell at once in a great precipice towards Geneva, going down three thousand feet in four or five cliffs, or steps. Now that whole group of cliffs had simply been torn away by sheer strength from the rocks below, as if the whole mass had been as soft as biscuit. Put four or five captains' biscuits on the floor, on the top of one another; and try to break them all in half, not by bending, but by holding one half down, and tearing the other halves straight up;—of course you will not be able to do it, but you will feel and comprehend the sort of force needed. Then, fancy each captains' biscuit a bed of rock, six or seven hundred feet thick; and the whole mass torn straight through; and one half heaved up three thousand feet, grinding against the other as it rose,—and you will have some idea of the making of the Mont Saléve.
May. But it must crush the rocks all to dust!
L. No; for there is no room for dust. The pressure is too great; probably the heat developed also so great that the rock is made partly ductile; but the worst of it is, that we never can see these parts of mountains in the state they were left in at the time of their elevation; for it is precisely in these rents and dislocations that the crystalline power principally exerts itself. It is essentially a styptic power, and wherever the earth is torn, it heals and binds; nay, the torture and grieving of the earth seem necessary to bring out its full energy; for you only find the crystalline living power fully in action, where the rents and faults are deep and many.
Dora. If you please, sir,—would you tell us—what are 'faults'?
L. You never heard of such things?
Dora. Never in all our lives.
L. When a vein of rock which is going on smoothly, is interrupted by another troublesome little vein, which stops it, and puts it out, so that it has to begin again in another place—that is called a fault. I always think it ought to be called the fault of the vein that interrupts it; but the miners always call it the fault of the vein that is interrupted.
Dora. So it is, if it does not begin again where it left off.
L. Well, that is certainly the gist of the business: but, whatever good-natured old lecturers may do, the rocks have a bad habit, when they are once interrupted, of never asking 'Where was I?'