References
- Kellogg , C. E. 1950 . “Soil,” . Scientific American , July
- Kuenen , P. H. 1960 . “Sand,” . Scientific American , April
- Sinnott , E. W. and Wilson , K. S. 1963 . Botany; Principles and Problems , 6th Edition , New York , N.Y. : McGraw-Hill Co. .
- The United States Department of Agriculture . 1957 . Soil, The Yearbook of Agriculture 1957 , Washington , D.C. : United States Government Printing Office .