Vivian Bushell, age 12, of Peoria, Illinois, for her question:

Does a quicksand have a bottom?

Naturally the soggy pit does not sink through the globe to China. A quicksand rests in the earth's crust    on a solid bottom that is seldom deeper than 30 feet. It may be only four, eight or ten feet deep. But a quicksand is even more dangerous than scarey bogs and swamps. All of these tricky booby traps are hard to spot. When exploring suspicious new territory, it is wise to probe the path ahead with a stick    especially low lying meadows that appear bright with healthy vegetation. This may cover a deep pit of soggy mud.

A quicksand is a mixture of sand and, usually, sea water, too thick to swim in and too thin to walk upon. It tends to form on a beach where rocky formations below the surface form a solid basin to trap a pocket of sand. The water is added by the tides, which come and go. When they drain out to sea, the pocket of sand may be left as dry and safe as any other patch of the beach. It is wise to test a newly found beach at various tide levels    for quicksands are cruel tricksters.