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 bottom of it inside.
But what is this high bit with E against it?
Those are the high hills round Bath, which we shall run through soon. They are newer than the soil here; and they are (for an exception) higher too; for they are so much harder than the soil here, that the sea has not eaten them away, as it has all the lowlands from Bristol right into the Somersetshire flats.
* * *
There. We are off at last, and going to run home to Reading, through one of the loveliest lines (as I think) of old England.
And between the intervals of eating fruit, we will geologize on the way home, with this little bit of paper to show us where we are.
What pretty rocks!
Yes. They are a boss of the coal measures, I believe, shoved up with the lias, the lias lying round them. But I warn you I may not be quite right: because I never looked at a geological map of this part of the line, and have learnt what I know, just as I want you to learn simply by looking out of the carriage window.
Look. Here is lias rock in the side of the cutting; layers of hard blue limestone, and then layers of blue mud between them, in which, if you could stop to look, you would find fossils in plenty; and along that lias we shall run to Bath, and then all the rocks will change.
* * *
Now, here we are at Bath; and here are the handsome fruit-women, waiting for you to buy.
And oh, what strawberries and cherries!
Yes. All this valley is very rich, and very sheltered too, and very warm; for the soft south-western air sweeps up it from the Bristol Channel; so the slopes are covered with fruit-orchards, as you will see as you get out of the station.
Why, we are above the tops of the houses.
Yes. We have been rising ever since we left Bristol; and you will soon see why. Now we have laid in as much fruit as is safe for you, and away we go.
Oh, what high hills over the town! And what beautiful stone houses! Even the cottages are built of stone.
All that stone comes out of those high hills, into which we are going now. It is called Bath-stone freestone, or oolite; and it lies on the top of the lias, which we have just left. Here it is marked F.
What steep hills, and cliffs too, and with quarries in them! What can have made them so steep? And what can have made this little narrow valley?
Madam How's rain-spade from above, I suppose, and perhaps the sea gnawing at their feet below. Those freestone hills once stretched high over our heads, and far away, I suppose, to the westward.
Now they are all gnawed out into cliffs,--indeed gnawed clean through in the bottom of the valley, where the famous hot springs break out in which people bathe.
Is that why the place is called Bath?
Of course. But the Old Romans called the place Aquae Solis--the waters of the sun; and curious old Roman remains are found here, which we have not time to stop and see.
Now look out at the pretty clear limestone stream running to meet us below, and the great limestone hills closing over us above.
How do you think we shall get out from among them?
Shall we go over their tops?
No. That would be too steep a climb, for even such a great engine as this.
Then there is a crack which we can get through?
Look and see.
Why, we are coming to a regular wall of hill, and -
And going right through it in the dark. We are in the Box Tunnel.
* * *
There is the light again: and now I suppose you will find your tongue.
How long it seemed before we came out!
Yes, because you were waiting and watching, with nothing to look at: but the tunnel is only a mile and a quarter long after all, I believe. If you had been looking at fields and hedgerows all the while, you would have thought no time at all had passed.
What curious sandy rocks on each side of the cutting, in lines and layers.
Those are the freestone still: and full of fossils they are. But do you see that they dip away from us? Remember that. All the rocks are sloping eastward, the way we are going; and each new rock or soil we come to lies on the top of the one before it. Now we shall run down hill for many a mile, down the back of the oolites, past pretty Chippenham, and Wootton-Bassett, towards Swindon spire. Look at the country, child; and thank God for this fair English land, in which your lot is cast.
What beautiful green fields; and such huge elm trees; and orchards; and flowers in the cottage gardens!
Ay, and what crops, too: what wheat and beans, turnips and mangold. All this land is very rich and easily worked; and hereabouts is some of the best farming in England. The Agricultural College at Cirencester, of which you have so often heard, lies thereaway, a few miles to our left; and there lads go to learn to farm as no men in the world, save English and Scotch, know how to farm.
But what rock are we on now?