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,
Divisions on a Ground Divisions on a Ground Divisions on a Ground: Essays on Canadian Culture is a collection of essays by Canadian literary critic Northrop Frye, edited by James Polk and published in 1982. The collection includes lectures, addresses and previously published articles by Frye. "Divisions on a Ground" presents Frye's theorizing about Canada with respect to three main themes: Canadian literary writing, university education in Canada and internationally, and a more general "social order" perspective. This collection diverges from Frye's better-known "" in its approach to Canada in that it does not present the "Canadian imagination" in isolation, but rather as one