1) W. L. Hill, “Superphosphate. Its History, Chemistry and Manufacture”, Agr. Res. Service, Washington D. C. p. 95-115 (1964).
2) W. H. Pierre and A. G. Norman (Editors), “Soil and Fertilizer Phosphorus” Academic Press Inc. New York IV, p. 348-9 (1953).
3) A. V. Kazakov, “The Phosphorite Facies and the Genesis of Phosphorites” Tran. Sci. Inst. Fertilizers and Insecto-Fungicides, No. 142 (pub. for 17th Int. Geol. Cong. Leningrad) p. 95-113 (1937).
4) V. E. Mckelvey, R. W. Swanson, and R. P. Sheldon, C. R. 19th Int'l Geol. Cong. Algiers, Comptes rendus. Sec. 11, fasc. 11, p. 45-64 (1953).
5) Duncan McConnell, Econ. Geol. 60. p. 1059-1063 (1965).