* * * * *

Now we are settled in the train. 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. I see now.

Then look at the sketch of the rocks between this and home. It is only a
rough sketch, of course: but it will make you understand something more
about the matter. Now. You see, the lump marked A. With twisted lines
in it. That stands for the Mendip Hills to the west, which are made of
old red sandstone, very much the same rock (to speak roughly) as the
Kerry mountains.

And why are the lines in it twisted?

To show that the strata, the layers in it, are twisted, and set up at
quite different angles from the limestone.

But how was that done?

By old earthquakes and changes which happened in old worlds, ages on ages
since. Then the edges of the old red sandstone were eaten away by the
sea--and some think by ice too, in some earlier age of ice; and then the
limestone coral reef was laid down on them, "unconformably," as
geologists say--just as you saw the new red sandstone laid down on the
edges of the limestone; and so one world is built up on the edge of
another world, out of its scraps and ruins.

Then do you see B. With a notch in it? That means these limestone hills
on the shoulder of the Mendips; and that notch is the gorge of the Avon
which we have steamed through.

And what is that black above it?

That is the coal, a few miles off, marked C.

And what is this D, which comes next?

That is what we are on now. New red sandstone, lying unconformably on
the coal. I showed it you in the bed of the river, as we came along in
the cab. We are here in a sort of amphitheatre, or half a one, with the
limestone hills around us, and the new red sandstone plastered on, as it
were, round the bo