12 In contrast, the old soil has well-developed Ay and AL herizons and supports dense vegetation, which produces a heavy litter fall during the dry season and which contributes to the redistribution of radionuclides in the system. Sea birds nest in the vegetation and land crabs, predominantly Birgus latro and Coenobita perlatus, burrow in the soil. Earthworms are seldom found and terrestrial isopods, although found in old soils on some islets, are few. There are also few soil insects, which are mainly tenebrionid and carabid beetles as well as ants. Depth Gradient of Gamma Spectra Old Soil The gamma spectra, with background subtracted, of the 0 to l-inch, 1 to 2-inch, and 9 to 10-inch depth increments from old soil collected in March 1959 are given in Fig. 5. The spectra of the increments between 2 inches and 9 inches have been omitted from the figure for clarity but show a gradual change from the condition at 1 to 2 inches to that at 9 to 10 inches. The radionuclides corresponding to the photopeaks are indicated in the figure. The photopeaks of co®?, zn°>, un>4, Ce 144 -Pr 144 and Eut5> show significant counts in the surface increments but are not detectable in samples from greater depths. The amounts of est3? and sp*?5 decrease and the proportions of Cs 13 Al 7 and