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 Void a parody of "noir" and horror fiction, with many stylistic tricks, gags, plot twists, and a grim conclusion. On many occasions it implicitly talks about its own lipogrammatic limitation, highlighting its unusual syntax. "A Void"<nowiki>'</nowiki>s protagonists finally work out which symbol is missing, but find it a hazardous topic to discuss, as any who try to bypass this story's constraint risk dying. Philip Howard, writing a lipogrammatic appraisal of "A Void" in his column "Lost Words", said "This is a story chock-full of plots and sub-plots, of loops within loops, of trails in pursuit of trails, all of which allow