Then a seed-planter sowed the grass. And finally Charlie used the strangest machine of all. It chugged and puffed and spit out great mouthfuls of hay, which fell over the newly-planted grass! The hay protected the grass seed and kept it moist until its roots were growing strongly in the soil. MORE ROAD WORK The road was finished now, but some of the machines still had work ahead of them. In fact, road work is never ended. All summer long, tractors pull mowing machines beside the highways, cutting the grass. Brush and small trees must be kept cleared away so that drivers can see ahead. In winter, the motor graders and the snow plows can keep the road clear. But in places where heavy snow piles up into drifts, caterpillar tractors often push special snow plows that eat through the drifts with powerful whirling blades. With one motion these plows dig out the snow and throw it off to one side of the road. [Illustration] The caterpillar treads work better in snow than wheels with tires. So the “cats” are used all winter long in the Far North. There they even pull whole trailer trains on runners. The one in the picture is hauling Muskeg schooners, which are really trailer houses on sleds. Muskeg is an Indian word for swamp. The cats pull the schooners over frozen, snow-covered swamps. You may wonder why anyone wants to use a trailer home in the roadless wastes of the Far North. The fact is that men work there the year round, prospecting for oil. When they think they have located oil there or anywhere else, well-drilling machinery goes to work. DRILLING MACHINES Everybody knows that oil wells and derricks go together. The tall derrick towers are needed to hoist drilling equipment in and out of the hole. [Illustration] When men start to drill a well, they fasten a cutting tool, called a bit, to a piece of pipe which hangs upright in the derrick. Machinery turns the whole thing round and round, so that the bit grinds down into the earth. When one length of pipe, called a joint, has almost disappeared into the hole, men screw another joint onto the top of it. Now the engine turns the double-length pipe, and the bit digs down deeper. Men, working on the floor and high up in the derrick, hoist more and more joints into position and screw them together as the bit goes on down. After a while, the bit gets dull. A new one must be put on. So, strong cables that run over wheels at the top of the derrick begin lifting the whole string of pipe out. Joint by joint, they unscrew the pipe and stack it out of the way. When the last joint comes up, men change the bit. Then back the pipe goes, joint after joint, into the hole. Wells must often be drilled more than two miles deep before the bit breaks through into an underground reservoir of oil. That means that the string of drilling pipe must be two miles long. The machines that help to handle it are very strong, but on many rigs, men have to use their own muscles a great deal, too.