Now let me tell you why I said that the piddock is one of the most wonderful of all the creatures which live in the sea. First of all, then, remember that the sea, acting by itself, has very little power to wash away chalk. For as soon as the waves begin to beat upon the face of a chalk cliff, they leave on it the spores, or seeds, of sea-weeds. Very soon those spores begin to grow, and before long the surface of the cliff is covered with masses of weed, so that the sea hardly touches the chalk underneath them at all. The waves might beat upon the cliffs for hundreds and hundreds of years without breaking it down. But the piddock comes and burrows into the chalk just below high-water mark. Backwards and forwards it goes boring on, till at last only thin dividing walls are left between its tunnels. Then the sea washes in, and breaks down these walls, so that the whole foundation of the cliff is cut away. The result is, of course, that before very long there is a landslip. Hundreds of tons of chalk come tumbling down into the sea. Then the piddocks begin work again a little farther back, and by-and-by there is another landslip. You can see the effects of the piddock’s work upon any part of the coast where there are chalk cliffs. Just look at the beach when the tide is out. You will notice long spits of weed-covered rocks, which sometimes run far out into the sea. Well, those rocks were not always rocks. They were once the bottoms of cliffs. But the piddocks and the sea, working together, cut the cliffs down; so that the sea gained, yard by yard, upon the land. Indeed, I think that it may be said, quite truly, that if it had not been for the work of the piddocks Great Britain would not be an island! At any rate we do know this, that once, a great many hundreds of thousands of years ago, Great Britain was not an island at all, but was joined to the mainland of the Continent of Europe. And we also know that the sea, acting by itself, could not possibly have cut a passage through what we now call the Straits of Dover. The piddocks helped it to do so! They kept on cutting away the foundation of the cliffs by boring backwards and forwards through the solid chalk, just below the level of the waves; and the sea finished the work which the piddocks had begun, by breaking down the thin dividing walls between their burrows. PLATE XVII THE LITTLE PIDDOCK (2 and 3) The common piddock grows to a length of from three to five inches, and is almost always white in colour, though sometimes it is stained by the rocks in which it lives. But there is another kind of piddock which is very much smaller, for its shells hardly ever measure more than an inch and a half in length, and are a good deal narrower in proportion to their size. This creature is called the Little Piddock. It is generally of a brownish yellow colour, and you may often find its burrows in great numbers in limestone rocks. [Illustration: PLATE XVII 1. THE PIDDOCK.