see and hear the battle.

A wave comes rolling smoothly on towards the shore. It reaches the land
and can go no further, and then, with a roar and a crash and splash of
sparkling foam, it breaks. It spreads into a sheet of foaming water,
and, after rushing as far as it can up the beach, it seethes back as the
next wave takes up the battle.

What a grinding and tearing, as wave after wave is hurled at the land!
That is the battle-cry of the land and sea! Most of the pebbles and the
sand on the beach have been won from the land in the great fight. We
might call them the spoils of war. Once they formed part of the solid
land, the rock or cliff. Now they are loose fragments spread for mile
after mile round our coast.

Every wave takes them up and has fine fun with them. Pebbles and sand
are picked up, swirled along, and thrown at the shore. They are sucked
back as the wave is broken by the land. And then the following wave
takes them, grinds them and scrubs them together. Thus they are jostled
hither and thither, up and down the coast; and, as a result of the long,
long fight, rocks and cliffs become pebbles, sand, or mud.

Now if you look at the pebbles on the shore you see that many of them
are smooth and round. Some are as round as the "marbles" you play with.
No wonder, for the mighty sea has scoured them with sand and rolled them
for miles.

As you know, the sea is not always at the same height. It falls and
rises. Twice in every day it _ebbs_ and _flows_; we call this movement
of the sea the _tides_. At low tide we can explore the very bed of the