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"Atoll, a coral reef surrounding a pool of shallow water, usually called a lagoon. The atoll is formed by the building of a coral reef on a circular or nearly circular foundation. It is usually broken in one or more places so that the lagoon is connected with the surrounding waters." -Foster, 1921

Atoll

"Atoll, a coral reef surrounding a pool of shallow water, usually called a lagoon. The atoll is formed…