A book entitled Earth is a basic reference textbook in many universities around the world. One of its two authors is Professor Emeritus Frank Press. He was the Science Advisor to former US President Jimmy Carter, and for 12 years was the President of the National Academy of Sciences, Washington, DC. His book says that mountains have underlying roots. These roots are deeply embedded in the ground, thus, mountains have a shape like a peg (see figures 1, 2, and 3).
Mountains have deep roots under the surface of the ground. (Earth, Press and Siever, p. 413.)
Schematic section. The mountains, like pegs, have deep roots embedded in the ground. (Anatomy of the Earth, Cailleux, p. 220.)
Another illustration shows how the mountains are peg-like in shape, due to their deep roots. (Earth Science, Tarbuck and Lutgens, p. 158.)