The question of the age of the Maitai Series is one of the most important which concern New Zealand geology, and one which has aroused the greatest controversy and uncertainty. F. von Hochstetter, before any distinctive fossils had been found in these rocks, considered that the “Maitai Series”, which form the hills bounding on the east and south-east the strip of fossiliferous Trias of the Nelson area, were of Triassic age, and underlay the sandstones with Monotis salinaria. In 1873 F. W. Hutton referred the Maitai to the Jurassic on the supposed occurrence of Inoceramus. A. McKay in 1878, during the survey of the Nelson district, found several fossils, obviously of late Palæozoic age, in the Maitai Limestone of the upper part of the lower Wairoa Gorge opposite a place called Martin's Saw-mill. Sir J. Hector identified these as Spirifera bisulcata, Productus brachythærus, Cyathophyllum, and Cyathocrinus. McKay also surveyed and collected from the Maitai slates and argillites at Wooded Peak, on the Dun Mountain Tramway, some five miles east of Nelson. A large bivalve shell having the prismatic structure and general outline and concentric plication of Inoceramus occurs here. McKay, however, in his report adds that “there are material differences between this shell and the ordinary forms of Inoceramus which may warrant its being considered the type of a new genus”.