"Hailstones," said Donald.
"Oh," said Susie, "I saw a hailstone once as big as an egg."
"The lakes are hollows in the ground filled with water. There are many small hollows, and some big ones, but there is one so great that we may call it immense. It is the largest hollow in the world—so large that it occupies three-fourths of the earth's surface."
[Illustration: Ocean islands]
"The ocean," said Frank.
"Yes, the ocean is only a great big hollow filled with water."
"How deep is the ocean?" asked Frank.
"Very deep in some places—deeper than the height of the highest mountains. In others it is very shallow. In some places bits and masses of land rise out of the ocean."
"Islands?" asked Donald.
"Four great masses of land rise above the ocean level. These immense rock masses are called—"