 Their interpretation of the data collected in both field and laboratory is that these stone balls were formed by high temperature nucleation of glassy material within an ashfall tuff, as a result of tertiary volcanism.Stirling was president of the Anthropological Society of Washington in 1934–1935 and vice president of the American Anthropological Association in 1935–36.He received the National Geographic Society's Franklyn L. Burr Award for meritorious service in 1939, 1941 (shared with his wife Marion) and 1958.