Excavators are labour-saving machines much employed at present for the removal of earth in the making of docks, railways, and the like. They are of two kinds, the first being a single scoop raised or lowered by crane mechanism, and arranged with jaws that cut out a certain quantity of earth on being drawn together by steam or other such motive power. The second is precisely similar to the steam-dredger with its endless chain of buckets. [Dredging.] The first possesses the advantage of variety in movement and general applicability, the second of economy in time required for the excavation of a given amount of material.