Trias–Jura? By M. Ongley. [Read before the Wellington Branch, October 13, 1936; received by the Editor, October 10, 1939; issued separately, June, 1940.] In New Zealand, if a greywacke formation is found that yields no evidence of its age, it is common practice to follow the usage initiated by Dr. Marshall and call it Trias-Jura. In the course of mapping Kaitangata Subdivision, the writer had to examine an area adjoining the “Trias-Jura” of Tuapeka Subdivision and to investigate this classification. Marshall (1918, N.Z. Geol. Surv. Bull., 19) classed the Otago Schist and the 30 miles of greywacke south of it as far as Nugget Point and the Kaihiku Range in the early Mesozoic portion of his Trias-Jura formation. This formation was based on his work in Nelson, of which he wrote, in the Handbuch der Regionalen Geologie, New Zealand, the following: “In 1908 and 1909 the writer examined this district in great detail and was satisfied that the rocks from the Dun Mountain to the Waimea Plain constitute a conformable series, but they are much and sharply folded. The commonest fossils are the definite Triassic forms described by Zittel: Monotis salinaria var. richmondiana Zitt., Halobia lomelli Wissm. Mytilus problematicus Zitt., Spirigera wreyi Zitt. However in the lowest beds of the series a few specimens of Trigonia were obtained and Gryphaea was found to occur occasionally with the Mytilus. This certainly justifies the use of the term Trias-Jura. The original specimens on which Hector's identifications were based are not now available, and no subsequent collectors have obtained the types he mentions; no forms, in fact, that are different from Trias-Jura types in other parts of the country.” In spite of the fact that Marshall's examination of the district satisfied him that the beds constitute a normal conformable sequence, his ideas of the structure and sequence cannot be accepted. For instance conglomerate beds found almost continuously along a line for thirteen miles and reaching in places 500 feet thick were dismissed as indicating “local changes in the conditions of sedimentation.” Further, his scepticism regarding McKay's finding of the Matai fossils (upper Palaeozoic) was shown as unjustified when Trechmann and Thomson, by following McKay's directions, recollected them as narrated by Trechmann (Geol. Mag., dec. 6, vol. 4, p. 54, 1917): “In October, 1915, when I was in the Wairoa Gorge in company with Mr. F. Worley, of Nelson, we made careful inquiries where ‘Martin's Saw-mill’ formerly stood, as it had disappeared since 1878. On returning two days later with Dr. A. Thomson we had the good fortune almost simultaneously to find the fossils at the place indicated…. “Two days later I visited in Mr. Worley's company the Dun Mountain tramway line, and at Wooded Peak, again following closely the instructions of McKay's report, we found the large bivalves exactly as he had described.”