Society for Testing and Materials, 1985, D 2487-83, Classification of Soils for Engineering Purposes: Annual Book of ASTM Standards. Vol. 04.08, pp 395–408. Earlier systems of historical interest Baldwin, M., Kellogg, C. E., & Thorp, J. (1938). Soil classification. In Soils and men: Yearbook of agriculture (pp. 979–1001). Washington, DC: U.S. Department of Agriculture. Simonson, R. W. (1989). Historical aspects of soil survey and soil classification with emphasis on the United States, 1899-1970. Wageningen, NL: International Soil Reference and Information Centre (ISRIC). Principles Eswaran, H., Rice, T., Ahrens, R., & Stewart, B. A. (Eds.). (2002). Soil classification : a global desk reference. Boca Raton, Fla.: CRC Press. Butler, B. E. (1980). Soil classification for soil survey. Oxford: Oxford Science Publications. Science, 96, Cline, M. G. (1949). Basic principles of soil classification. Soil Science, 67(2), 81-91. Cline, M. G. (1963). Logic of the new system of soil classification. Soil 17-22. Webster, R. (1968). Fundamental objections to the 7th approximation. Journal of Soil Science, 19, 354-366. Terzaghi Karl (1924). Soil Mechanics in Engineering Practice, Wiley-Interscience; 3 Sub-edition (January 1996, ) kevin Hart (1923) . founded it Numerical classification McBratney, A. B., & de Gruijter, J. J. (1992). A continuum approach to soil classification by modified fuzzy k-means with extragrades. Journal of Soil Science, 43(1), 159-175. External links A Compendium of On-Line Soil Survey Information - Soil Classification for Soil Survey by D. G. Rossiter OSHA Soil Classification Types of soil Pedology