Near horizontally bedded Upper Eocene sediments comprising Blanche Point Marls, Tortachilla Limestone and South Maslin Sands, have been test bored at Hackham in the Noarlunga Basin, in the search for a bentonite - type clay deposit which might provide a useful local source of raw material for the petroleum drilling and foundry industries. Reserves of 400 000 cubic yards have been proved, which on the basis of sieve analysis and fines mineralogy contain more than 50% montmorillonite in the clay fraction. The testing of other outcrops of the Upper Eocene sediments in the Noarlunga and Willunga basins is recommended. At present, the bulk of requirements for bentonite in Australia are met by imports from the U.S.A.