A very curious machine of the walking type has been developed for excavating machines that operate in soft swampy ground. The machine actually walks over surfaces that a light carriage could not negotiate. It consists of a large central turntable flanked on each side by a pair of broad and long tread plates which serve as feet. When the dredge is to be moved, it plants the feet on the ground, lifts up the turntable, moves it forward, and sets it down again; then the feet are lifted, moved forward, and planted on the ground again while the turntable is moved forward again. When it is desired to make a turn the machine is swiveled around to the desired direction while sitting on the turntable with its feet raised clear of the ground. Of course the speed of such a machine is very low, but transportation is of secondary consideration. The main purpose of the machine is to excavate ditches in soft ground and only occasionally does it have to move its position. The turntable provides a broad base that distributes the load over a comparatively large area which prevents the machine from sinking into the mud, and if it should sink into a soft spot it lifts itself out vertically instead of having to roll out. “CATERPILLAR” TRACTION Long ago it occurred to inventors that a machine could travel over trackless wastes if they carried their own tracks with them. The idea dates back more than a century, but only in comparatively recent times has it been developed to a practical stage. The track-laying mechanism takes different forms, but in one prominent type it consists of a series of plates linked together to form a chain or belt that passes around a series of wheels. As the machine progresses the plates are successively laid down in front of the wheels and picked up behind them. The wheels consist of a large number of rollers whose axles are spring-supported so that they are capable of a certain amount of vertical movement and as the belt they roll upon is made up of separate plates they can adjust themselves to irregularities of the ground and creep over an uneven surface. Its close resemblance to the creeping locomotion of a caterpillar has led to the adoption of the trade name “caterpillar” by one of the large tractor manufacturers. The tractor belt is driven by spur wheels at each end and the rollers serve merely to distribute the weight of the machine along the belt. The traction is exceedingly great because the belt is broad and long, giving it a large gripping surface. For the same reason it will not sink into plowed ground. Because of its flexible tread surface it will creep over rocks and stumps, waddle down into a ditch and climb up the opposite bank. So powerful is it that it will crash through underbrush with ease and even small trees yield before it. It will run over soft mud, deep sand, and even snow with equal facility. The tread belts on either side of the tractor are separately driven and by making one belt run faster than