Sinkhole may exhibit a visible opening into a cave below. In the case of exceptionally large sinkholes, such as the Minyé sinkhole in Papua New Guinea or Cedar Sink at Mammoth Cave National Park in Kentucky, an underground stream or river may be visible across its bottom flowing from one side to the other. Sinkholes are common where the rock below the land surface is limestone or other carbonate rock, salt beds, or in other soluble rocks, such as gypsum, that can be dissolved naturally by circulating ground water. Sinkholes also occur in sandstone and quartzite terrains. As the rock dissolves,
A Star Is Bored he believes to be another gun (in reality it is HIS gun bent around so that it points at his hindquarters) sticks up through a hole in the ground just behind him! Daffy retracts his gun; the "other" gun does the same. Daffy does this two or three more times before he decides to try a small experiment. He ties a red ribbon around the barrel of his gun, then sticks it into the tree, and looks behind him. The ribbon on the gun in the ground is white with red polka dots, leading Daffy to believe it to be