One of its two authors is Professor Emeritus Frank Press. His book says that mountains have underlying roots.
Mountains have deep roots under the surface of the ground.
The mountains, like pegs, have deep roots embedded in the ground. Another illustration shows how the mountains are peg-like in shape, due to their deep roots. This is how the Quran has described mountains. So the most suitable word to describe mountains on the basis of this information is the word peg, since most of a properly set peg is hidden under the surface of the ground. The history of science tells us that the theory of mountains having deep roots was introduced only in the latter half of the nineteenth century.