The Iheya island is located to the northwest of the Okinawa island and belongs to the pre-Tertiary zone of the Ryukyu arc. The island is composed of pre-Tertiary rocks and Quaternary deposits. It. however, lacks the Pleistocene coral reef limestone, although it lies in the coral sea area at present. The present writer summarizes the results of his geomorphological investigation at the island as follows: 1. Gentle erosional slopes which fringe the NE-SW stretching mountain land in the direction of the major geological structure, are considered to have been formed during the early and middle Pleistocene. The slope deposits are weathered deeply and reddish in colour, and form the basements of the coastal terraces. The pre-cyclic valley floors and small erosional basins have remained in the mountain land, especially in the sandstone areas, concordant with the erosional level of gentle slopes. 2. The higher coastal terrace which stands 25-30m above the present sea level was built after, at least, a glacial period successive to the formation of the gentle erosional slopes. The terrace surfaces, in places, are covered with reddish weathered talus and debris related to the gentle erosional slopes. The terrace is considered to have been formed at the high sea level during Mindel-Riss Interglacial. 3. Leaving the glacial period after the Interglacial, the sea level raised again higher and stayed for a comparatively long period during which the 15 m coastal terrace was constructed. This high sea level may be correlated to that of Riss-Wrum Intarglacial. 4. The regressional sea towards the low sea level of Warm Glacial cut the 9m and 6m coastal terraces. The new talus and debris of new gentle erosional surface cover the terrace surfaces. The consolidated and old coastal dune which extends below the present sea level grew between the commencement of the regression and the Postglacial transgression. 5. The coast maintained the sandy beach during Postglacial transgression until the sea level reached its peak, so-called Daly Level at which the off-shore bars blocked the small bays and formed the back marshes with thin mud deposits. 6. The high beach ridges and beach rocks were formed on the bars at Daly Level. The new dune sand was also blown up behind the sandy beach. Judging from the heights of the raised coastal features, Daly Level is considered to have been about 4 m above the present sea level. 7. Main notches and benches are believed to have developed during Rottnest Emergence below Daly Level. 8. Present coral reefs are of fringing or pseudo-barrier reefs, and have grown up since Daly Level in the same manner. Present reefs are not well developed because the steep mountain slopes covered with reddish weathered deposits, in many places, directly compose the basement of the coast.
