The writer reviews investigations on coral reefs in the East Indies carried out especially during the last 15 years before the war. Every atoll and barrier reef studied in some detail shows conclusive evidence of subsidence. The extreme thickness of some reefs, as demonstrated by their steep submarine slopes, cannot be explained by Glacial Control only. The influence of shifting sea level during the ice ages has been of minor importance on the East Indian reefs. In this region, as a rule, narrow lagoons are shallower than wide lagoons; the phenomenon is obviously related to aggradation of the bottom.
It is claimed that solvent action of sea water in the tropics is limited to action above the surface of the sea. The paper bears on the important influence of prevailing wind and wave action on the upper structure of reefs. Additional examples are given of sea currents as factors of morphological importance. The great influence of sedimentation and of a recent world-wide sinking of sea level is stressed. Elevated atolls, reef terraces, and tilting movements are considered. Results are mentioned of investigations on such subjects as the depth penetration of light and oxygen consumption.