As a result of the International Indian Ocean Expedition, the bottom of the Indian Ocean is now one of the best known areas of the ocean floor. The Mid-Indian Ocean Ridge, a rugged mountain range, lies in the centre of the Indian Ocean. North-northeast trending fractures offset the axis of the ridge. In the Arabian Sea these fractures are right lateral; in the southwest Indian Ocean they are left lateral. Displacements range from a few miles to over 200 miles. The northeast Arabian Sea and the Bay of Bengal are occupied by huge abyssal cones built by sediments discharged from the Indo-Gangetic plain. Extensive abyssal plains lie seaward of the abyssal cones. In low latitudes smooth topography is characteristic of the continental rise, the abyssal cones, and the oceanic rises. However, near the polar front smooth `swale' topography laps over the normally rugged Mid-Oceanic Ridge. This `swale' smoothing appears the result of the higher organic productivity of the Antarctic seas. Microcontinents, mostly linear meridional ridges, are unique features of the Indian Ocean. These massive but smooth-surfaced blocks contrast markedly with the broad rugged Mid-Oceanic Ridge.