In physical geography the name applied to a cavity resulting from the solution of rock under the action of water, and forming, or having at some period formed, the entrance to a subterranean stream-channel. Such holes are common in calcareous (limestone or chalky) districts, or along the line of outcrop of a limestone belt among non-calcareous strata. These cavities are also known as sinks, dolinas or butter-tubs, and by other local names, and sometimes as potholes; the last term, however, is also synonymous with Giant's Kettle. See Cave.