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?”

Dora.  When the two halves of the dining-table came separate, yesterday, was that a “fault”?

L. Yes; but not the table’s.  However, it is not a bad illustration, Dora.  When beds of rock are only interrupted by a fissure, but remain at the same level, like the two halves of the table, it is not called a fault, but only a fissure; but if one half of the table be either tilted higher than the other, or pushed to the side, so that the two parts will not fit, it is a fault.  You had better read the chapter on faults in Jukes’s Geology; then you will know all about it.  And this rent that I am telling you of in the Saleve, is one only of myriads, to which are owing the forms of the Alps, as, I believe, of all great mountain chains.  Wherever you see a precipice on any scale of real magnificence, you will nearly always find it owing to some dislocation of this kind; but the point of chief wonder to me is the delicacy of the touch by which these gigantic rents have been apparently accomplished.  Note, however, that we have no clear evidence, hitherto, of the time taken to produce any of them.  We know that a change of temperature alters the position and the angles of the atoms of crystals, and also the entire bulk of rocks.  We know that in all volcanic, and the greater part of all subterranean, action, temperatures are continually changing, and therefore masses of rock must be expanding or contracting, with infinite slowness, but with infinite force.  This pressure must result in mechanical strain somewhere, both in their own substance, and in that of the rocks surrounding them; and we can form no conception of the result of irresistible pressure, applied so as to rend and raise, with imperceptible slowness of gradation, masses thousands of feet in thickness.  We want some experiments tried on masses of iron and stone; and we can’t get them tried, because Christian creatures never will seriously and sufficiently spend money, except to find out the shortest ways of killing each other.  But, besides this slow kind of pressure, there is evidence of more or less sudden violence, on the same terrific scale; and, through it all, the