These little people of the sea-floor furnish one of the most assuring evidences we have that although the continents rose out of the sea, they will never go under the sea again. These are shell creatures found in the slime dredged from the bottom of the deepest parts of the sea. The shells of creatures that live near shore are found in abundance in our rocks, but these types are found only in the deepest seas. So, since the deep down-wrinklings of the earth that make the sea-basins have never risen, it is probable they never will; and consequently that the up-wrinkles--the continents--will continue to stay above the waters. ] It's a wonderful old story, isn't it? But more wonderful still, it always seemed to me, is the story of how they found all this out. Who do you suppose first told about it? The last people you would ever think of, I'm sure--the oysters! WHAT THE OYSTERS TOLD XENOPHANES It sounds like a passage from "Alice in Wonderland," or "Through the Looking-Glass," doesn't it? But it's a fact. Away back, more than 2,000 years ago, a wise Greek called Xenophanes, who lived in a place called Colophon, and so was called Xenophanes of Colophon, said that he thought the rocks of the mountain sides must once have been under the sea because of the oyster shells that were found embedded in many of them. [Illustration: HOW THE OYSTERS TOLD THE GREAT SECRET Here is a good example of the thing that led wise old Xenophanes of Colophon to make the startling assertion that the mountains were once at the bottom of the sea. These are the shells of oysters embedded in limestone--which, by the way, the shells of the oysters themselves helped make--and this piece of stone is from the top of a high mountain. ] "For," said Xenophanes of Colophon, "how else could the oyster shells have got there? Who ever heard of oysters climbing a mountain?" Another evidence that lands come up out of the sea is this: Even before the days of Scott and Maryatt and Fenimore Cooper, men--and, of course, boys--were interested in caves that face upon the sea. They are such jolly places for pirates, and for boys playing pirate, and for mermaids drying their hair. It was plain that down where the waves in storms could reach them the sea itself bored out these caves. But how about those caves in the cliffs high above the waves? The sea must have made them, too, once upon a time when the land was lower in the water. Then the land was raised. Still more striking was the fact that not only caves but old sea beaches were found on hill and mountain slopes far from the sea, sometimes hundreds of miles inland. You can tell the old beaches by their shape and the way in which the pebbles are sorted by size, just as you find them on beaches to-day. THE BAKED APPLE AND THE BULGING WORLD