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II. The “Two-Limestone” Theory.
Park's “two-limestone” theory, as stated above, was an attempt to solve the problem of the “Pareora fauna.” This problem first presented itself to the New Zealand geologists when Haast submitted four collections of fossils from different localities to Hutton (1887, p. 430) for identification. The latter referred all the shells to the Pareora (Awamoan) horizon above the limestone. Haast himself was convinced that one of the collections had been obtained from beds which lay below the limestone. Other collections of fossils examined by Hutton were determined by him as “Pareora,” and in all cases he referred the beds to an horizon above the limestone. Haast and the officers of the old Geological Survey agreed with Hutton that some of his “Pareora” faunas came from above the limestone, but the field evidence convinced them that other collections of fossils determined by Hutton as “Pareora” came from below the limestone. Park (1905, p. 491) clearly recognized the difficulties, and attempted
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a solution by his theory that there were two limestone horizons, separated by the Hutchinson Quarry and Awamoan beds (Pareora); or, in other words, that there was but one “Pareora fauna,” lying between two limestones, the lower being called the Ototaran stone and the upper the Waitaki stone.
The present writer (refer to Thomson, 1915, p. 123), after an excursion to the Waihao district of South Canterbury, was convinced that, where the full series was developed, there was but one limestone present. An examination of the fauna beneath the limestone showed that it bore a remarkable resemblance to the fauna above the limestone in the Waihao district, where the beds occur in the same section. This view was supported by Thomson (1915, p. 123), who subsequently visited the Waihao district. Park, however (1905, p. 510), had given a section at Kakanui in which his two limestones were shown separated by the fossiliferous beds. The present writer (1916, pp. 22–25) sought to prove that this section had been misinterpreted, and that only one limestone was present, with the fossiliferous beds lying above it. Park in his latest work has evidently accepted this interpretation of the section, for the Awamoan beds are now placed at the top of the sequence in the Oamaru and Kakanui districts. As pointed out above, however, he still maintains that the limestone of the Waitaki Valley is distinct from the limestone of the Oamaru district.