L. Well, I must keep it within the best compass I can.  When rocks either dry from a moist state, or cool from a heated state, they necessarily alter in bulk; and cracks, or open spaces, form in them in all directions.  These cracks must be filled up with solid matter, or the rock would eventually become a ruinous heap.  So, sometimes by water, sometimes by vapor, sometimes nobody knows how, crystallizable matter is brought from somewhere, and fastens itself in these open spaces, so as to bind the rock together again with crystal cement.  A vast quantity of hollows are formed in lavas by bubbles of gas, just as the holes are left in bread well baked.  In process of time these cavities are generally filled with various crystals.

Mary.  But where does the crystallizing substance come from?

L. Sometimes out of the rock itself; sometimes from below or above, through the veins.  The entire substance of the contracting rock may be filled with liquid, pressed into it so as to fill every pore;—­or with mineral vapor;—­or it may be so charged at one place, and empty at another.  There’s no end to the “may be’s.”  But all that you need fancy, for our present purpose, is that hollows in the rocks, like the caves in Derbyshire, are traversed by liquids or vapor containing certain elements in a more or less free or separate state, which crystallize on the cave walls.

Sibyl.  There now;—­Mary has had all her questions answered:  it’s my turn to have mine.

L. Ah, there’s a conspiracy among you, I see.  I might have guessed as much.

Dora.  I’m sure you ask us questions enough!  How can you have the heart, when you dislike so to be asked them yourself?

L. My dear child, if people do not answer questions, it does not matter how many they are asked, because they’ve no trouble with them.  Now, when I ask you questions, I never expect to be answered; but when you ask me, you always do; and it’s not fair.

Dora.  Very well, we shall understand, next time.

Sibyl.  No, but seriously, we all want to ask one thing more, quite dreadfully.

L. And I don’t want to be asked it, quite dreadfully; but you’ll have your own way, of course.

Sibyl.  We none of us understand about the lower Pthah.  It was not merely yesterday; but in all we have read about him in Wilkinson, or in any book, we cannot understand what the Egyptians put their god into that ugly little deformed shape for.

L. Well, I’m glad it’s that sort of question; because I can answer anything I like to that.

Egypt.  Anything you like will do quite well for us; we shall be pleased with the answer, if you are.

L. I am not so sure of that, most gracious queen; for I must begin by the statement that queens seem to have disliked all sorts of work, in those days, as much as some queens dislike sewing to-day.

Egypt.  Now, it’s too bad! and just when I was trying to say the civillest thing I could!