It takes considerable time for fertile soil to cover the surface of mountain. Many ingredients and some other factors are also required. First rocks must be broken down by wind and rain to pieces to become the base of soil. Fertile soil must include water and air inside. Having those in the base of soil several organisms such as plants, micro fungi and bacteria work together. The secretion of bacteria makes a small lump of a particle in the base of soil. Earthworms are also important. They eat soil and excrete feces of which form are small lumps as well. Then roots of plants and micro fungi connect these small lumps to each other to become a large lump. Both small and large lumps create many gaps among them. These gaps are able to hold air and water. Besides inside of each small lump there are cavities in which air and water stay. On such fertile soil trees and other large plants can easily spread their roots to use water and air inside.