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 Rickle in Time being and instructs Morty and Summer to break off their collars, but the resulting chain of uncertainty further splits their realities into dozens of different timelines. After defeating the testicle monster, Rick notes that time is falling apart. Summer's collar transports her back to her time, but one of the Mortys' collar is broken. With the garage falling away piece by piece, the Morty with the broken collar falls into the spaceless void and Rick jumps after him. He gives Morty his collar and instead prepares to face death. But then, Rick spots Morty's collar floating below him, fixes it,