In pure hydraulic dredging systems, the digging and lifting force is either pure suction, suction assistance, or entirely. They are best suited to digging relatively small-sized loose material such as sand and gravel, marine shell deposits, mill tailings, and unconsolidated overburden. Hydraulic dredging has also been applied to the mining of deposits containing diamonds, tin, tungsten, niobium-tantalum, titanium, monazite, and rare earths. The digging power of hydraulic systems has been greatly increased by the addition of underwater cutting heads. The cutter suction dredge has a rotary cutting head or other excavating tool for loosening and mixing soil at the face of the mine - hydraulic dredging . Normally, the dredge is held in place during cutting by a pile called a spud. Winches and wire ropes are used to swing the dredge in an arc around the spud until all the material in the arc has been removed. The dredge is then moved ahead and the process repeated. The c...