L. And when you mend a decayed stuff with strong thread, does not the whole edge come away sometimes, when it tears again?
Dora. Yes; and then it is of no use to mend it any more.
L. Well, the rocks don't seem to think that: but the same thing happens to them continually. I told you they were full of rents, or veins. Large masses of mountain are sometimes as full of veins as your hand is; and of veins nearly as fine (only you know a rock vein does not mean a tube, but a crack or cleft). Now these clefts are mended, usually, with the strongest material the rock can find; and often literally with threads; for the gradually opening rent seems to draw the substance it is filled with into fibres, which cross from one side of it to the other, and are partly crystalline; so that, when the crystals become distinct, the fissure has often exactly the look of a tear, brought together with strong cross stitches. Now when this is completely done, and all has been fastened and made firm, perhaps some new change of temperature may occur, and the rock begin to contract again. Then the old vein must open wider; or else another open elsewhere. If the old vein widen, it may do so at its centre; but it constantly happens, with well filled veins, that the cross stitches are too strong to break; the walls of the vein, instead, are torn away by them; and another little supplementary vein—often three or four successively—will be thus formed at the side of the first.
Mary. That is really very much like our work. But what do the mountains use to sew with?
L. Quartz, whenever they can get it: pure limestones are obliged to be content with carbonate of lime; but most mixed rocks can find some quartz for themselves. Here is a piece of black slate from the Buet: it looks merely like dry dark mud;—you could not think there was any quartz in it; but, you see, its rents are all stitched together with beautiful white thread, which is the purest quartz, so close drawn that you can break it like flint, in the mass; but, where it has been exposed to the weather, the fine fibrous structure is shown: and, more than that, you see the threads have been all twisted and pulled aside, this way and the other, by the warpings and shifting of the sides of the vein as it widened.
Mary. It is wonderful! But is that going on still? Are the mountains being torn and sewn together again at this moment?
L. Yes, certainly, my dear: but I think, just as certainly (though geologists differ on this matter), not with the violence, or on the scale, of their ancient ruin and renewal. All things seem to be tending towards a condition of at least temporary rest; and that groaning and travailing of the creation, as, assuredly, not wholly in pain, is not, in the full sense, 'until now.'
Mary. I want so much to ask you about that!
Sibyl. Yes; and we all want to ask you about a great many other things besides.
L. It seems to me that you have got quite as many new ideas as are good for any of you at present: and I should not like to burden you with more; but I must see that those you have are clear, if I can make them so; so we will have one more talk, for answer of questions, mainly. Think over all the ground, and make your difficulties thoroughly presentable. Then we'll see what we can make of them.