Michelle Harakal, Age 10, Of Fu1lerton, Pa., for her question:     

Does every continent have a continental shelf?     

The ocean basins are vast pits with steep sides two to three miles deep. The sea fills these yawning chasms and spills over to drown strips of coastline around the continents.  These shallow waters are called continental shelves.  As a rule, they slope gently to a depth of 1200 to 1800 feet where they plunge into the basins.     Off our pacific coast, the shelf is about 20 mi1es wide; off the northern Atlantic states, it is 150 miles wide.  South of Cape Hatteras, the she1f narrows, and the shores of Florida plunge almost directly into deep water.  Near and off the shores of the Antarctic, the continental shelves are too narrow to be ca11ed shelves at all.