Mike potter Jr., age 13, of Nashville, Tenn., for his question:

CAN YOU EXPLAIN QUICKSAND?

Quicksand is a dangerous deposit of fine sand that is so heavily

filled with water that it actually flows easily. Each smooth, rounded grain of sand is lubricated by the surrounding water and each grain can then slide past the next grain.

A bed of quicksand will generally form where rivers deposit fine sand over underlying rock or clay. Water can't escape because the clay or rock keeps the quicksand fall of water.

Building foundations must be set 1n solid ground and engineers must take care not to have part of a structure on quicksand. Sometimes it is necessary to sink a caisson through the quicksand, so the foundation can be anchored below the soft material.

A whole railroad train, including the engine, sank into a bed of quicksand at Pueblo, Colo., in 1875. Tracks had not been properly laid. The sand was probed to a depth of 50 feet but there was no sign of the train