25 first inch and remain at approximately the same level from 7/8 inch to 1-1/2 inches in depth. RAD IOAUTOGRAPHS Young Soil Undisturbed Radioautographs of cores taken in 1963 show marked differences in the distribution of radioactivity. Fig. 12 shows photo- graphs and the corresponding radioautographs of sections of cores of young soils from an undisturbed area (Fig. 2) and from an area subject to erosion (Fig. 13) and an old soil (Fig. 3). The radio- activity corresponds closely to the dark area in the photograph of the core from the undisturbed young soil. This dark area is composed almost entirely of a mixture of soil algae, forming a crust which has retained most of the fallout radionuclides. Exroded In an eroded area of young soil the radioactivity is associated with large coral fragments which are infiltrated with algae. This area is subject to erosion by both wind and water, which accounts for the coral fragments containing algae and radionuclides occurring below the soil surface. Radio- activity is not associated primarily with smaller particles as zs