Terry Dahms, age 11, of Ids Grove, Iowa, for the question:

What is shale?

Shale is one of the most plentiful rocks of the earth's crust. It occurs in flat layers which split open like rocky pages. Much of it is drab gray in color but it may be black, dark red or dark green. Shale is made from fine particles of clay and the color depends on the impurities in the clay.

The shales are classed as sedimentary rocks. They were laved down by running water. Muddy clays, silts and sands are toted by swift water and dropped as the stream slows down. Layers of soft mud accumulate and later dry out into beds of shale. If the shale is buried under heavy pressure it turns to hard brittle slate.

Shale is not durable enough to make a good building material. It is, however, interesting to the fossil collector. Fossil leaves, plants and even animals are often found pressed between its rocky pages.