Margie Letson, age 10, of Past Brunswick, New Jersey, for her question:

How is clay formed?

The earth has dozens of different clays and all of them are muddy mixtures of very fine particles. It is easy to mistake them for ordinary mud, but genuine clay is something special. When it is wet, it is much more slippery than ordinary mud and the moist mixture feels somewhat oily. This is because its mineral ingredients are small, flat particles. When wet, fine particles of this sort tend to slip and slide across each other.

The various clays are made from common minerals in the earth's crust. The main ingredients are tough silicates and aluminum, though many other minerals may be present. The original rocky materials were washed and worn, smashed and pounded into fine fragments by rains and running water. Great piles of these clay making particles were deposited in hollows and valleys, along the shores of rivers and 1akes .