In west Nelson traces of oil are found at Karamea, Reefton, Dobson, and Kotuku. At Reefton the oil occurs in connection with certain shales underlying the coal. As pointed out by Morgan and Webb,* the source of the oil is undoubtedly the beds of the coal series. At Karamea and Reefton the shales and claystones which carry the oil are upturned by powerful faults, and the structure is synclinal.
At Dobson the bore from which the oil issues penetrates the western limb of the Brunner anticline. Between this bore and the crest of the anticline runs a branch of the great Mount William fault, to the west of which the oil will occur. At Kotuku the oil-permeated gravels lie over the northern continuation of the Ross fault, and it seems feasible to suppose that these supplies of petroleum are soaking up along this fault. The structure of the underlying coal-beds will be monoclinal.
[Footnote] * Morgan: Geol. Surv., 3rd Ann. Rep. (n.s.), pp. 9, 10. Webb: Idem, p. 23.