The following are a few myths about quicksand:

Quicksand sucks you down like a vacuum cleaner. In fact, quicksand doesn't pull you down any more than a swimming pool does. Quicksand is more buoyant than water, so it's actually easier to float in quicksand than in a swimming pool.

Quicksand is a bottomless pit. Most patches of quicksand are a few inches to a few feet deep.

Quicksand is always made of sand. In addition to sand, clay, swamps, and silt can all become what scientists call "quick."

Quicksand occurs when water is present and flowing through an earth material. The water travels through pore spaces and lifts and moves material making the sediment act as a liquid.

If you do fall into quicksand, remember not to panic. You'll probably only sink a few feet. Swim or walk to solid ground.
Lifted and adapted from http://www.greenapple.com/~words1/quicksand.html