That stretch of sea between Africa on the W. and Australia, Java, and Sumatra on the E., which separates in the N. into the Arabian Sea and the Bay of Bengal; the monsoons, or trade-winds, blow here with great regularity; from April to October they are strong from the SW., from October to April more gentle in the opposite direction; there are many islands and reefs of coral formation, such as the Maldive group; St. Paul's and Mauritius are volcanic, while Madagascar and Ceylon are typical continental islands.