Keystone Species that Live in the Mountains (Kid's Guide to Keystone Species in Nature)

Most arches built today contain a single building block at the top that is the most important piece. This special piece can be found in the arches of soaring cathedrals, doorways in temples, and even simple buildings made out of wooden blocks. It is called a keystone, and it holds everything else together. Remove the keystone and the building or doorway is likely to collapse.