17 fortuitous since the available Sr?0 in the soils, that fraction extractable into normal neutral ammonium acetate, is somewhat less than the total. | From Figure 3 it is clear that most of the fallout has been deposited since the beginning of 1953. The change in average annual slope indicates at least qualitatively the increasing annual contribution of stratospheric debris to total fallout. The general agreement between the change in soil level ad cumulative fallout in rains during the intervening period is graphic indication that the scavenging of the atmosphere by rains is the primary mechanism of fallout. Sampling of rains with tubs continuously exvosed will include collec- tion of dry fallout of large particles which may be appreciable for considerable distances downwind of test areas during the first few days following an atomic test.