First, the teacher illustrates the block-like nature of limestone, or karst bedrock. The fractures and blocks are irregular. They may not be continuous in any direction. When water seeps down from the surface, it dissolves limestone along these fractures. The rate of dissolving depends upon how much acid or water is in the rock, and how much acid is in the water.
Water is more acidic at levels near the water table.
Some areas of the United States have bedrock close to the surface. In areas of the West and Midwest, land was once covered by glaciers during the ice age. Several hundred feet of gravel may cover the bedrock. Children in these areas may rarely see bedrock, and may have a hard time imagining it. Karst topography develops many interesting landforms.