Mark Lindsay, age 14, of Las Vegas, Nev., for his question:

ARE THERE MANY KINDS OF EARTH MOVING MACHINES?

Power shovels and draglines are the main types of earth moving machines. Power shovels have buckets called clamshells that dig into the earth and shovel it up.,The bottom of the clamshell opens to dump the dirt into a truck for removal. A dragline is used mainly to excavate holes.

The heavy duty tractor, when fitted with tracks to grip the ground and with a large, movable blade attached is front, is called a bulldozer. It is used to clear brash, remove rocks and level ground.

A scraper may be pulled by a tractor or it may be self powered. Dirt is scraped into the container and then may be spread out or carried off for disposal elsewhere.

Similar to the scraper is the grader, a self propelled machine with a long adjustable steel blade. Graders are primarily finishing machines.

Lightweight tractors fitted with wheels instead of tracks are used for light construction jobs. A backhoe scoops out shallow ditches.