The calcareous remains of tiny creatures called coral polyps and hydrocorals provide the basic building material for the reefs while the remains of coraline algae and organisms called polyzoas provide the cement that holds the structure together. When fossilized, such reefs and the debris eroded from them form thick limestone units.
Humans have felled and cleared the island's natural cover of tropical forest so extensively that soil erosion has been vastly accelerated.