Speleogen

A speleogen is a geological formation within a cave that has been created by the removal of bedrock, rather than as a secondary deposit. They are typically formed in limestone or dolostone solutional caves. The United States Code defines speleogens as "relief features on the walls, ceiling, and floor of any cave or lava tube which are part of the surrounding bedrock, including anastomoses, scallops, meander niches, petromorphs and rock pendants in solution caves and similar features unique to volcanic caves."