And what do you want to know first?
More about the new rocks being lower than the old ones, though they lie on the top of them.
Well, look here, at this sketch.
A boy piling up slates?
What has that to do with it?
I saw you in Ireland piling slates against a rock just in this way.

And I thought to myself--"That is something like Madam How's work." How?
Why, see.

The old rock stands for the mountains of the Old World, like the Welsh mountains, or the Mendip Hills.

The slates stand for the new rocks, which have been piled up against these, one over the other.

But, you see, each slate is lower than the one before it, and slopes more; till the last slate which you are putting on is the lowest of all, though it overlies all.
I see now.