mountains, which once was coral reef, and is now the Severn sea; and by
the time you have eaten your breakfast we shall steam in through a crack
in that coral-reef; and you will see what you missed seeing when you went
to Ireland, because you went on board at night.

* * * * *

Oh! Where have we got to now? Where is the wide Severn Sea?

Two or three miles beyond us; and here we are in narrow little Avon.

Narrow indeed. I wonder that the steamer does not run against those
rocks. But how beautiful they are, and how the trees hang down over the
water, and are all reflected in it!

Yes. The gorge of the Avon is always lovely. I saw it first when I was
a little boy like you; and I have seen it many a time since, in sunshine
and in storm, and thought it more lovely every time. Look! there is
something curious.

What? Those great rusty rings fixed into the rock?

Yes. Those may be as old, for aught I know, as Queen Elizabeth's or
James's reign.

But why were they put there?

For ships to hold on by, if they lost the tide.

What do you mean?

It is high tide now. That is why the water is almost up to the branches
of the trees. But when the tide turns, it will all rush out in a torrent
which would sweep ships out to sea again, if they had not steam, as we
have, to help them up against the stream. So sailing ships, in old
times, fastened themselves to those rings, and rode against the stream
till the tide turned, and carried them up to Bristol.

But what is the tide? And why does it go up and down? And why does it
alter with the moon, as I heard you all saying so often in Ireland?

That is a long story, which I must tell you something about some other
time. Now I want you to look at something else: and that is, the rocks
themselves, in which the rings are. They are very curious in my eyes,
and very valuable; for they taught me a lesson in geology when I was
quite a boy: and I want them to teach it to you now.

What is there curious in them?

This. You will soon see for yourself, even from the steamer's deck, that
they are not the same rock as the high limestone hills above. They are
made up of red sand and pebbles; and they are a whole world younger,
indeed some say two worlds younger, than the limestone hills above, and
lie upon the top of the limestone. Now you may see what I meant when I
said that the newer rocks, though they lie on the top of the older, were
often lower down than they a