Before the era of modern diesel or gasoline powered equipment, the existing machinery was steam powered. Animal or steam-powered skidders could be used to haul harvested logs to nearby rail roads for shipment to sawmills. Horse driven logging wheels were a means used for moving logs out of the woods. Another way for transporting logs to sawmills was to float them down a body of water or a specially-constructed log flume. Log rolling, the art of staying on top of a floating log while "rolling" the log by walking, was another skill much in demand among lumberjacks. Spiked boots known as "caulks" or "corks" were used for log rolling and often worn by lumberjacks as their regular footwear.