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 are.
But how do you know that they lie on the limestone?
Look into that corner of the river, as we turn round, and you will see with your own eyes. There are the sandstones, lying flat on the turned-up edges of another rock.
Yes; I see. The layers of it are almost upright.
Then that upright rock underneath is part of the great limestone hill above. So the hill must have been raised out of the sea, ages ago, and eaten back by the waves; and then the sand and pebbles made a beach at its foot, and hardened into stone; and there it is. And when you get through the limestone hills to Bristol, you will see more of these same red sandstone rocks, spread about at the foot of the limestone-hills, on the other side.
But why is the sandstone two worlds newer than the limestone?
Because between that sandstone and that limestone come hundreds of feet of rock, which carry in them all the coal in England. Don't you remember that I told you that once before?
Oh yes. But I see no coal between them there.
No. But there is plenty of coal between them over in Wales; and plenty too between them on the other side of Bristol. What you are looking at there is just the lip of a great coal-box, where the bottom and the lid join. The bottom is the mountain limestone; and the lid is the new red sandstone, or Trias, as they call it now: but the coal you cannot see. It is stowed inside the box, miles away from here. But now, look at the cliffs and the downs, which (they tell me) are just like the downs in the Holy Land; and the woods and villas, high over your head.
And what is that in the air? A bridge?