A similar landform is the tepui, which has a rather different origin. A body of hard rock resists erosion. It was originally inside a body of softer rock such as limestone, which got eroded away to form a plain. The more resistant rock is left behind as an isolated mountain. The term is used for the table-top mountains of South America. Auyán-tepui in the Guiana Highlands, Venezuela is the source of the Angel Falls, the tallest waterfall in the world. It is 19 times higher than Niagara Falls.