26 Ve Sr90 Content of Foreizn Soils The results of Ssr70 analyses for all foreign soil samples assayed since the ‘publication ‘of Chicago Sunshine Bulletin ilo. 11, December 1, 1955, are: summarized in Table 6, Resvits for earlier foreign soil measurements, which include most of the data for soils collected during and »rior to the Spring of 195l, have been reported by W. F. Libby.? The results reflect the substantial increase in the world-wide cistrim-~ tion of Sr? fallout following the CASTLE tests. The increase is particularly striking for the southern hemisphere sammles which show about an order of magnitude increase in the sr90 soil content for the period from Spring 195) to January 1956, Two of the South American samples (Beltsville :/56456 from Lima, Peru and . #56UL7 from Antofagasta, Chile) are representative of areas of very low rain~ fall. Comparing their results with those for the Sao Paulo, Brazil and Anto~ fagzasta, Chile soils indicates a striking dependence of the fallovt on rain- fall, The result for the Prawley, California soil (CL 1127, reported on page ll, this report), which shows <0, Sunshine Units, corresponding to < 0.6 millicuries of Sr90 per square mile, is equally convincing in this respect. It wovld appear thet, except within several thousand miles down- wind of test areas where large particles of dry debris may fsll out directly for a short period following a test shot, precipitation must be tne only important mechanism of fallovt. This dependence can be further tested by relating the Sr90 soil level to rainfall information for areas. remote from test sites, The latitude dependence of fallovt, pointed out by W. F, Libby, 3 should be taken into account when such a correlation is attempved.