On enormous farms where very heavy work must be done, there are often crawler tractors to do it. Instead of tires they have caterpillar treads that give a better grip on the ground. Then they can pull a whole string of plows the way you see them in the picture, staggered out behind. This kind of tractor was first named caterpillar by only one manufacturer. But people liked the idea, and they began to call all crawlers caterpillars. A caterpillar is powerful enough to push a snow plow, too. Or it can bulldoze out a hole for a watering pond or a cellar for a new building. BUILDING MACHINES Charlie is the man who can tell you about driving a caterpillar tractor. He works in a city, helping to put up big buildings, and he knows how to use other construction machines, too. In fact, Charlie grew up with machines, for his father and his uncles and his grandfather were construction workers. It often happens that families pass along their knowledge of building from the older to the younger men, and they are very proud of their skills. Charlie uses the caterpillar tractor with a bulldozer blade to push heaps of earth and rock into a pile, ready for the shovel to load on a truck. [Illustration] [Illustration] [Illustration] People often call the shovel a “steam shovel,” but that’s not its right name. You hardly ever see a real steam shovel any more. Years ago the big digging machines were driven by regular steam engines. Before they could start to work on a job, the men had to build a fire in the boiler and wait until they had enough steam pressure to make the shovel go. Of course, this wasted a lot of time. So, when very strong gasoline and Diesel engines came along, builders began using them for their shovels instead of steam engines. Many shovels and other construction machines ride to work on long gooseneck trailers. They travel faster that way than they could on their own crawlers. And, in cities, the caterpillar treads might damage the pavement. To load and unload a shovel, the operator sets a short ramp of heavy planks against the trailer. Then the shovel creeps up and down on its own crawlers. The kind of shovel that’s used on a job depends upon the work that must be done. If a basement has to be dug through hard rocky earth, Charlie may operate a crowd shovel, which crawls down into the hole. The shovel has a heavy dipper with teeth along the rim. When it digs, it crowds its teeth down into the ground. Charlie, sitting inside the cab, called the house, swings the dipper outward and up, then dumps the load into a truck. [Illustration] Another shovel digs in the opposite way. It’s called a pull shovel. The teeth dig down and toward the driver. It can work from a bank and doesn’t have to go down inside the hole at all.