sixty-one small islets ranging in size from a fraction of an acre to the largest, Rongelap, which is four miles long and one-half mile across at its widest point. There is one small islet on the western reef and the other islets extend along the northern, eastern and southern reefs. The islets on the northern reef are not as well developed as those to the east and south. There are two seasons--a dry season from December to March and a wet season from April to November. Annual rain- fall is less than fifty inches, and there is no well-developed fresh-water lens. Some important features of Rongelap Atoll including aerial photographs are given by Wiens (1962). Classification and mapping of the soil types at Rongelap Atoll were reported by Kenady (1962). The parent material is primarily calcium carbonate, originating from corals, minifera, coralline algae and mollusk shells. small amount of pumice drift in the soils. fora- There is a very Since these soils contain no inorganic colloids, exchange capacity and organic content are linearly related. In some areas, particularly along the seaward sides of the islets, buried AL horizons are found as deep as eighty inches (Fig. 1). These highly organic horizons presumably result from storm debris covering previously established soil and vegetation. The pH, determined in the field from a 1:1 soil-water ratio with a Beckman Model N-2 pH meter, is generally between