Rock is the commonest thing in the world. And to many of us it seems the most solid and enduring. Yet all around us we see evidence that rocks are constantly changing. At the seashore we see great stretches of sand which the waves have worn from the rocks. On the highway a sign warns us "Beware of falling rocks," and we know that bits of the mountain are weathering off. Or we may see a great boulder perched in the middle of a cow pasture and find that a glacier carried it to this spot a million years ago.

But although mountains wear away, new ones always build up again. For rock is made as well as unmade. A volcano, for example, builds itself up with lava coming from deep within the earth. But some of our mountains have been created by great pressures within the earth that have caused layers of rock to split or tilt or even to push above the earth's surface.

And always this change is creating different kinds of rock. Some is as shiny as any glass we manufacture. Some sparkles with flecks of minerals. Some is as soft as chalk. Some is in six-sided crystals. And some shows the pattern of the tiny seashells from which it is made.

In All About Our Changing Rocks, Anne Terry White tells of the vast changes that have produced these different rocks and explains how to identify the rocks we see around us.

From the dust jacket