1. Technical Recommendations for Highways: Draft THR 14;National Institute For Transport And Road Reserach,1980
2. CSIR Res. Rep.;F. Netterberg,1971
3. NETTERBERG F. (1980): Geology of southern African calcretes. 1. Terminology, description, macrofeatures and classification. Trans. Geol. Soc. S. Afr., vol 83, pp 255–283.
4. PAIGE-GREEN P. (1980): Durability testing of, and specifications for, degrading Dwyke tillite in southern Africa. Proc. 7th Reg. Conf. Afr. Soil Mech. Fndn. Engng., Accra, Ghana, June 1980, pp 209–213.
5. SHERGOLD F.A. and HOSKING J.R. (1959): A new method of evaluating the strength of roadstone. Roads and Road Constr., vol 37, no. 438, pp 164–167.