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Volume 42, 1909
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2. “On the Glacial Till in Hautapu Valley, Rangitikei, Wellington,” by Professor Park.

Abstract.

The triangular area lying between the Manawatu River and Wanganui is occupied by a gravel drift 400 ft. or 500 ft. thick, which, along its inland border, rests against a series of marine clays of the Pliocene age that are horizontal or dip gently towards the sea. These clays, along their northern limit, skirt the upland plains that wrap around Ruapehu. In a few places they are intercalated with thin beds of shelly limestone or irregular layers of hard calcareous nodules. The gravels comprise the coastal country (highly cultivated), and the clays are found inland over the hills and ridges covered with dense forest, and still further inland where there are forty or fifty miles of undulating grass land.

Through this country flowed a number of rivers—Rangitikei, Hautapu, Turakina, and Wangaehu. Beginning at Waiouru, on the inland grass lands, and proceeding eastward, the hills are found to present the smooth, flowing outlines, truncated crests, and terraced, slopes characteristic of glacial erosion. The higher hills are dome-shaped, the lower hummocky and whale-backed in form. At Taihape the hills are beautifully rounded, coned, and domed; at Mataroa there is a fine example of a U-shaped valley. A large stretch of country, from Karioi, near Ruapehu, across the ridges to Hautapu Valley, is covered with a sheet of glacial boulder clay or till. The till consists of clays, or clays mixed with andesite blocks, or andesite blocks, or andesite blocks alone. It is mostly unstratified. The boulders range from small blocks up to masses 6 ft. to 8 ft. in diameter. The thickness of the till varies from nothing to 60 ft., so far as may be seen, and in many places rests on hill-summits 300 ft. and 400 ft. above the floor of the old glacial valley. On the Waiouru plateau andesite boulders are present in large number 2,660 ft. above sea-level. Above Taihape blocks are abundant; below, clays predominate. The latter extend down the Hautapu Valley for twenty-six miles, ending near Utiku at a height of 1,220 ft. above the sea. The andesite blocks have travelled forty-five miles from their source at Ruapehu, and are spread over a width of ground varying, so far as may be seen, from two to five miles. The andesitic material has been transported over a ridge of hills 600 ft. to 900 ft. high above the Karioi Flat, from the slopes of Ruapehu to its present position, by ice.

It would appear that there was a differential movement in the Ruapehu Glacier, the bottom stream going south through the Karioi Basin and along the Wangaehu Valley, and the upper and greater stream flowing south-east across the divide into Hautapu Valley, carrying a load of andesitic débris. The deeply eroded surface of the marine Pliocene clays show its tracks, and the old glacial valley can be easily traced from any high point of view. The Rangitikei Glacier flowed southward from the Kaimanawa Mountains and Ruahine Range, and deflected the Hautapu Glacier westward towards the Turakina. These mountains are composed of argillite and grauwacke: hence, until it met the Hautapu Glacier near Utiku, the Rangitikei Glacier carried only argillite and grauwacke boulders.

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It was pointed out that Ruapehu is only 3/2o further north than Boulder Lake, in Collingwood, the most northerly point at which evidence of ancient glaciation is known in the South Island. He considered the Hautapu till too widespread and variable to be regarded as a terminal or lateral moraine: therefore it must be boulder clay or till formed mainly of interglacial débris deposited by the Hautapu Glacier as it retreated on its centre of movement at Ruapehu.

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He believed that this glacial period must have been in the Pleistocene age, which made New Zealand's ice age contemporaneous with that of the Northern Hemisphere. In this period Ruapehu was a centre of dispersion, from which glaciers radiated into the Rangitikei, Wangaehu, Upper Wanganui, and Upper Waikato, the latter flowing into Taupo Basin through Rangipo Desert.

Professor P. Marshall stated that he did not at all agree with Professor Park's views. The Ruapehu country was country with which he was perfectly familiar. He did not regard its appearance as being due to glacial action: it was, he believed, solely the result of river-action. At a comparatively recent geological period it had been on the sea-floor. It had been raised up 4,000 ft. by degrees, and rivers had thereby flowed all over it, depositing the gravels spoken of. Professor Park spoke of and no doubt regarded them as tills; but to the speaker they were nothing more than river-gravels, deposited at different times. After referring to certain geographical features of the country, Professor Marshall said that Ruapehu had been examined by many geological students, who had quite failed to discover the deep-scored valleys or any other signs of glaciation. The region had recently been the subject of a detailed geographical survey by Mr. R. Speight, who found no such evidence of glaciation. He personally had gone there in his young days, hoping to distinguish himself, but he had come away again without having found any proof of glaciation. He considered that there were no traces of glaciation in any of the mountain-ranges referred to by Professor Park; but that depended, after all, in what way different geologists read certain signs. He would personally regard the boulder-clay, if he looked at it in the same light as Professor Park looked at it, as undoubted proof of glaciation at Tongariro, for it was to be found there. How did Professor Park account for the absence of erratics, which should have been present in the case of such a glacier as had been described? Of course, they might occur, but had not been described. And surely there would have been a terminal moraine as plainly distinguishable as that at the Taieri, in the case of a glacier forty-five miles long. Professor Marshall concluded by saying that many geologists had given their decisions against the theory of a glacial period in any part of the North Island.

Mr. G. M. Thomson, M.P., said that all botanical evidence was dead against the glaciation theory, so far as he knew.

Professor Park, in replying, said that Professor Marshall was under an entire misapprehension. There was no river-gravel or water-worn material in the deposit, which consisted of piles of angular volcanic blocks that were largest and most numerous at the southern limit—that is, farthest from their source at Ruapehu—which, of course, would not be the case with river-material. He was the only geologist who had made a detailed examination of that country, having spent the summer of –87 making a geological survey of the Main Trunk route as far as Ruapehu, on behalf of the New Zealand Government. The evidence that he had now brought forward was quite new to geologists, the country over which the deposit was spread being covered with dense forest until quite recently. There was, Professor Park said, no other agency than ice capable of transporting such masses of rock so far from their source and spreading them over hill and dale.

The further consideration of the subject was adjourned to a special meeting of the Institute to be held on the evening of the 24th instant.