Is it true that most of the world is sea?

It is true that the great oceans cover by far the largest part of the earth. Only just over one quarter of our world is dry land    and this includes all the big continents and the little islands.

It is estimated that about 71 per cent of the world is covered by water. Only about 29 per cent is dry land,

Ruth Wirt, age 12, of Seattle, Washington for her question:

What causes quicksand?

We are all used to exciting tales about bogs and quicksands. The

hero steps upon a piece of innocent looking ground, which turns out to be soft. He tries to step back, or reach hard ground beneath, and begins to flounder. He is caught in a quicksand and the mushy ground seems to pull him down and down. Being the hero, however, someone comes along and nulls him out, all muddy »» but in the nick of time„ When the fleeing villain steps into one of these tricky booby trap s however, he generally sinks floundering to his doom.

Such bogs and quicksands do exist and they are very dangerous indeed. But they are far more plentiful in adventure stories than they are in real life,

Quicksands are a mixture of sand and water    often flowing water, Most sand, as you know, feels gritty to the touch. Each little grain of sand is sharp and angular. Some sands, however, are worn into grains like tiny smooth balls. They are the more slippery sands and less able to support heavy footsteps.

Sometimes a stretch of this smooth slippery sand rests on a bottom of hard clay. Water can seep into the sand but cannot seep through the hard clay below. It makes the sand into a layer of soft mush. The mixture of smooth sand and water is far softer than the sand alone. It cannot support even a pebble, let alone a heavy foot¬step. It is a quicksand, and whomever steps upon it will sink down, since the hard bottom may be many feet below, the hero or the villain may well sink above his head    if not rescued.

At times these stretches of smooth sands era found in areas of tidal waters of flowing rivers, for a few hours they may be quite dry and safe. Then in comes the water, flooding them and turning them into soft mush. If the water comes from a tide of flowing river it continues to flow, only more slowly. The villain or hero is drawn along with the moving water and seems to be pulled or sucked down into the quicksand.

A bog may be still be trickier. It often looks like a bed of soft green moss    which it is. For generations the moss may have been growing in a pool or lake. Each new crop has grown upon the one below it till the old lake is filled with layers of decaying vegetation called peat. This water logged peat is not firm enough to support the hero or the villain and down he goes.

Though bogs and quicksands    may be many feet deep, somewhere below there is a layer of solid ground. This, however, is no comfort to the unlucky person floundering about on the surface,