1. Code of stratigraphic nomenclature;American Commission on Stratigraphic Nomenclature;Am. Assoc. Petroleum geol. Bull.,1961
2. Bassett , M. G. Cocks , L. R. M. Holland , C. H. Rickards , R. B. Warren , P. T. 1975 The type Wenlock Ssries Rep. Inst. geol. Sci. no. 19
3. A concise guide to stratigraphical procedure;Harland;J. geol. Soc. London,1972