Explanation:

Limestone and chalk are sedimentary rocks of organic origin and in its pure state, limestone is made up of calcite or cacium carbonate.Limestone is soluble in rain-water, which, with carbon-di-oxide from the air, forms a weak acid. A region with a large stretch of limestone therefore possesses a very distinct type of topography – Karst topography.Karst regions have a bleak landscape. In areas where there are alternating beds of rocks(shales, sandstones, quartzites) with limestones or dolomites in between or in areas where limestones are dense, massive and occurring as thick beds, cave formation is prominent.Water percolates down either through the materials or through cracks and joints and moves horizontally along bedding planes. It is along these bedding planes that the limestone dissolves and long and narrow to wide gaps called caves result.