This view is along Audubon Avenue in Mammoth Cave (part of the Historic Cave Tour route). Note the flat-lying layers of Mississippian limestone in the cavern walls in contrast to the brown cave earth (soil with rubble) on the cavern floor. The limestone formed from lime mud and fossil remains deposited in a shallow interior seaway basin during Mississippian time. This resulted in the formation of the three named limestone rock formations in which the cavern system formed; these include the St. Louis Limestone, Ste. Genevieve Limestone, and Girkin Formation, from oldest to youngest, respectively. The huge passageways and lack of speleothems (stalactites stalagmites, flowstone, etc.) are typical of caverns in the Mammoth Cave region. Mammoth Cave is an "erosional cave" carved by underground streams rather that the more "dissolution-style" caverns like Carlsbad Caverns in New Mexico.