How is a coral reef made?

A coral reef is usually made by the earth and a host of living creatures working together. The ground work may be a rocky shoal or maybe the cone of an old volcano on the floor of the sea. Its top reaches up near the surface. There the sunlit waters make life easy for the tiny coral creatures to build their stony apartment houses.

There are countless kinds of coral, each building its own type of home. Soon the underwater hill is covered with various buildings of coral   and the little animals continue to build one apartment house upon another. Soon the underwater hill is covered with coral stone and we have a coral reef.