Okinawa is nearly midway between Japan and Formosa. This report deals with the southern third of the island, and particularly with the structural geology and water resources. The rocks present are Paleozoic schists, the Shimajiri formation of Miocene-Pliocene age, the Ryukyu limestone of upper Pliocene or lower Pleistocene age, and Recent beach sands, coral reefs, and alluvium. In southern Okinawa the Shimajiri formation (Miocene-Pliocene) laps upon the schists (Paleozoic) and was folded before the deposition of the Ryukyu limestone (Pliocene or Pleistocene). The Ryukyu limestone and older rocks were later gently folded along northwest-southeast axes. Compaction of the sediments over a buried ridge of schist created the Buckner anticline, the axis of which extends north-n rtheast and south-southwest through the area mapped. Faults parallel with this axis are regarded as causally related to it. Major physiographic effects are discussed.

Large streams, some of which must be dammed if water is to be available during low-flow periods, and several very large springs are major sources of water. Wells are practicable in the limestone in relatively few places and will have rather small yields. Limited sand deposits will furnish small supplies of water but only very small yields are to be expected from the alluvium and the Shimajiri formation.