Abstract: A dragged or self-propelled unit has drag shoes or other means to dislodge nodules from the sea bed into a duct which may be associated with nozzles to project fluid against the nodules. The duct increases substantially in cross-section, thereby slowing the velocity of a stream formed by the nodules, accompanying silt and water. The slowed nodules and silt are caused to follow divergent separate paths within the unit, the nodule path being relatively below the silt path, and the nodules are removed from the duct upstream of the final outlet by which silt and water depart the unit.