It is generally agreed that the main plateau of Western Australia has probably stood above sea-level since the earliest geological times, and has perhaps been a land area since the Archæan. Marine deposits lie against its northern, western, and southern borders, but none are known upon the plateau itself; but through the depression of Lake Cowan Kainozoic marine deposits have extended northward into the Dundas Goldfield at Norseman. These marine deposits include a deep lead with sponges which were described by Dr. Hinde (Bull. Geol. Surv. W.A., No. 36, 1910, pp. 7–24, pls. i–iii) and some patches of limestone which occur on the surface around Norseman. They have been described by Mr. A. Gibb Maitland, 1908 (“Recent Advances in the Knowledge of the Geology of West Australia,” Rep. Aust. Assoc. Adv. Sci., vol. xi, p. 153, 1906), and by Mr. W. D. Campbell (“The Geology and Mineral Resources of the Norseman District, Dundas Goldfield,” Geol. Surv. West Aust., Bull. 21, p. 22, 1906).