cradle-rocker noun in placer mining, a trough on a rocker shaken to separate gold flecks from sand and earth CANADA
A cradle-rocker is a trough on a wooden or metal rocker, to wash and shake [potentially gold-bearing] muddy gravel in water. The prospector who performs such a task may also be called a cradle-rocker. — Bill Casselman, CanadianWords, p. 166, 1995