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Geology of the Provinces of Canterbury and Westland, New Zealand : a report comprising the results of official explorations

Age and Thickess

Age and Thickess.

From the nature of the lowest beds of this formation, we must conclude that they were only deposited after the strata forming the Waipara or cretaceo-tertiary series had undergone considerable changes, and a large amount of denudation. Moreover, it is clear that these older marine beds, in many instances, were uplifted from the ocean, and that the newer beds were deposited upon them, either as littoral page 315or even as fresh water deposits; however, there is no doubt that afterwards the country sank again considerably below the sea-level, because beds belonging to this formation can be traced in the Southern Alps to an altitude of 5000 feet, unless we assume that some portion of the ranges underwent greater subsidence and elevation than others, for which, at least on so large a scale, no evidence can hitherto be found. Thus after the cretaceo-tertiary beds had been raised in succession to near or above the sea-level, during which they were so much destroyed that only in favourable localities some portions were preserved, new beds, first of littoral origin, and afterwards, as the country gradually sank, of a more pelagic character, were deposited above them. Of course the beds in question are not quite coeval, although occupying the same relative positions, as it is evident that those strata in the higher regions, or where the sinking of the ground was slower than in other portions of the country, must be of somewhat younger origin, a fact which may in a great measure account for some want of uniformity in their fossil contents. I wish also to point out another difficulty, the solution of which is of considerable importance for the classification of the beds in question. In the greensands of the Kakahu and Waihao a number of fossils have been collected by me, which Captain Hutton places with the Pareora formation, as for instance, Turitella ambulacrum and Pleurotoma Buchanani. These greensands are overlaid by calcareous greensands, with all the characteristic fossils of the Oamaru formation, on the edges of which the Pareora formation reposes unconformably, consequently a careful study of the more extended collections from these beds is needed to settle this point to my satisfaction. Concerning the age, I have already pointed out that it is exceedingly difficult to assign to these beds their exact position, when using for them any European nomenclature. However, as Dr. Zittel and Dr. Stache have both come to the conclusion, after studying carefully the fossils collected in this formation by Professor von Hochstetter, that they ought to be classed with the upper Eocene, I do not see any reason to depart from this opinion; although Captain Hutton, in his Report on the Geology of Otago, is inclined to include them with the lower Miocene. The thickness of the whole series of beds belonging to this formation is very considerable, and might in the average be 1500 to 2000 feet. In conclusion, I wish to say that 1 have adopted Captain Hutton's designation of Oamaru formation for this assemblage of beds, as the first fossils collected and described were derived from that locality.