"= 50\5 %, %. cline, at a rate of about 8 feet per hour. The distribution of radioactivity within the mixed layer was not homogeneous at the time of sampling. In three other surveys during 1956 and 1958 in which samples were collected up to six weeks after detonation, the radioactivity also was not distributed homogeneously in the mixed layer. the 1954 test series, However, one year after the radioactivity in the water above the thermocline was well mixed, from which it is concluded that the time required for fallout materials in the surface waters of the ocean to mix thoroughly is greater than six weeks and less than a year. Below the thermocline, hours after fallout, in the period from 28 to 48 the radioactivity in the particulate form descended at more than 10 meters per hour, four times the rate of movement through the mixed water layer (Lowman 1960). ‘The increased rate of movement is assumed to be the gravitational effect upon the heaviest fraction of the par- ticulate matter. The chemical and physical form of fallout materials as they enter the sea may change upon interaction with the Salts and other materials in the sea. Fallout that enters the sea as particulate matter may go into solution, and material in the tonic form may change to the particulate