Major rock units on Cap Island are granitic gneisses and foliated granite of assumed Archaean to Early Proterozoic age (Sleaford Complex), and aeolianites and calcretes of Middle Pleistocene Bridgewater Formation. On Waldegrave Islands, similar aeolianites overlie Middle Proterozoic, massive, pinkish red granites dated at about 1460 Ma. The 1 silicate analysis supports the trend for granites of islands in the Investigator Group, i.e. of higher SiO2 and K2O contents than average granites'.