29) Ve the north and eastern perimeter of the lagoon, the concentrations range from 0.3] to 0.47 pCi/g. These stations contained debris from most of the detona- tions conducted in the atoll. The range of values for unsupported 210p, in lagoon sediments (9.0 to 1.1 pci/g) may reflect the hydrology and sedinentation rates in the water column above the various collection sites. supported 210 The un- Pb concentrations measured may thus result largely from natural aeolian and pluvial processes . 5.2 Distribution of Findely Divided Sediments Many of the samples collected for analysis in this study were found to consist predominantly of coralline particles which are much smaller in size than natural fiarshall Island atoll sediments as described by Emery et al. (op. cit.) and Anikouchine (op. cit.}. These sediments were probably pulverized and distributed in the lagoon after each nearshore detonation. Because finely grained (pulverized) sediments contained the highest concentrations of radioactivity measured, it would seem reasonable to attempt to corre- late the concentration of radioactivity with the proportion of grained sediments present in each of the samples. The proportion of finely divided material in each sample was estimated visually. More precise measurements would have to be based on particle size and component statistics due to the smooth nature in which artificially produced and naturally fine-grained components grade together in some samples. In addition, photomicrographs were taken of surface sediments collected by coring at Station B-20 to estimate the range of particle size present ina lagoon surface sediment which was finely divided. Surface sediments collected from stations C-], 3, 4 (Bravo Crater), B-2 and B-20 consisted of fine-grained material. Surface sediments collected from stations C-6, C-8, B-2] and B-30 contained small proportions of slightly