76 Proceedings. 



The systems of ore-dressing explained were as follows : — 



(1.) Water concentration, based upon the action of this fluid upon minerals of 

 different specific gravity. 



(2.) Magnetic separation, based upon the fact that certain minerals are paramagnetic, 

 whilst others are diamagnetic. 



(3.) Oil concentration, based upon the power oil has of adhering to certain minerals, 

 whilst other minerals are not affected. Oil, being lighter than water, then rises to the 

 surface, carrying those minerals it adheres to with it. 



(4.) Flotation processes, in which bubbles of gas are made use of to buoy up certain 

 minerals which are specially attachable to gas-bubbles ; other minerals not being so 

 attachable are not buoyed up. The vacuum process, using both oil and gas, was also 

 mentioned. 



(5.) Electrostatic repulsion process, in which use is made of the fact that mineral 

 particles which are good conductors are Instantly repelled when brought into contact 

 with an electrically charged body, whilst non-conductors are not repelled for some time, 

 and may be drawn out of the path they are following. 



2. " On the Grlacial Till in Hautapu Valley, Rangitikei, Wellington," 

 by Professor Park. 



Abstract. 



The triangiilar 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 milesyof 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 east- 

 ward, the hills are foimd 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 beavitifully 

 roimded, 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 alone. It is mostly unstratified. 

 The boulders range from small blocks up to masses 6 ft. to 8 ft. in diameter. The thick- 

 ness 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 gomg south throiigh the Karioi Basin and along the Wangaehu 

 Valley, and the upper and greater stream flowing south-east across the divide 

 into Hautapvi Valley, carrying a load of andesitic debris. 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 west- 

 ward towards the Tvirakina. These mountains are composed of argillit© and grau- 

 wacke : hence, until it met the Hautapu Glacier near Utiku, the Rangitikei Glacier 

 carried only argillite and grauwacke boulders. 



It was pointed out that Ruapehii is only l^° further north than Boulder Lake, in 

 CoUingwood, 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 debris deposited by the Hautapu Glacier as it retreated on 

 its centre of movement at Ruapehu, 



