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,
Collapse into Now Collapse into Now Collapse into Now is the 15th and final studio album by the American alternative rock band R.E.M., released on March 7, 2011, on Warner Bros. Produced by Jacknife Lee, who previously worked with the band on "Accelerate" (2008), the album was preceded by the singles, "It Happened Today," "Mine Smell Like Honey", "Überlin" and "Oh My Heart". Regarding the album's title, lead singer Michael Stipe noted, "It's the final thing I sing, the last song on the record before the record goes into a coda and reprises the first song. In my head, it's like I'm addressing