re i- 35 Figure & represents the activity at each of the five depths sampled relative to the highest activity at each station of the Marsh survey, and Figure 9 represents the same thing for the Walton survey. In general, the presence of relatively higher levels of aotivity at greater depths at the Walton stations corresponds to the situation at the Marsh stations except in the area south and weet of 12° N and 157° E, where the Marsh stations had a marked IMIR UREA SbSy BE itegOT chartA ye fa<p OREO “ORAS preponderance of aotivity in the surface water. The Walton sur- vey was made during the test series when radioactive materials in the water had had only a few days or at most, a few weeks, moved by ocean currents from the area of fallout. to be In addition, the bulk of the activity was found to the north and northwest of the test site. Barnes? reports that the surface layers in this region move about three times faster than the layers at 300 meters, and Yoshida | shows the westward velocity of the surface water as about 14 times the velocity at 40 meters at 17° N. It seems possible, therefore, that the Marsh stations south of 12° N and west of the test site represent, for the most part, a region which received its radioactivity via the ocean currents. Stations 4 to 9 are exceptional in this region but they are also stations with high levels of activity (Pigs. 3 and 5, and Table 1), probdably due to fallout from tests made after the completion of the Walton survey. There are unusually ‘high levels of radioactivity at depths of 50 m to 100 m at the three stations immediately east of Eni- wetok and at station 68 which is about 2° N of Bikini. The theo