136 Transactions. 



There is no evidence that the Hautapu did at any time drain the slopes 

 of Euapehu ; but if it did, then obviously its upper sources have been 

 pirated by the Wangaehu — possibly in the late Pleistocene. 



The Hautapu is a tributary of the Rangitikei River. The latter rises 

 in the Kaimanawa Range, composed of Lower Mesozoic greywacke and slaty 

 shale, but in its middle and lower course the river passes over Younger 

 Tertiary marine clays which wrap around the older rocks, and in places 

 rise on the flanks of the range to a height of 4,000 ft. above the sea. The 

 Tertiary formation extends southward to the sea in the form of a great 

 gently sloping plain, now deeply dissected by many rivers and their numerous 

 tributary streams. The slope of this plain coincides approximately with 

 the dip of the strata. 



The clays are intercalated at intervals with wedge-shaped beds of impure 

 shelly limestone that attain their greatest thickness in the neighbourhood 

 of the old shore-line. 



The Hautapu Stream throughout its whole length lies within the area 

 occupied by the Tertiary clays. Near the sources of the stream the clays 

 are intercalated with a few irregular beds of shelly limestone, seldom more 

 than a few yards thick. 



Going southward, following down the Hautapu Valley, the first great 

 pile of andesitic blocks occurs at Turangarere, twenty miles as the crow 

 flies from Ruapehu. Still greater piles occur at Mataroa, thirty miles from 

 Ruapehu, and at Taihape, six miles south of Mataroa. The piles at Mataroa 

 and Taihape are linked up by many isolated blocks, some of great size, 

 perched on the ridges on the north side of the valley. 



It is noticeable that the andesitic piles themselves and their constituent 

 blocks become larger and larger as the distance from Ruapehu increases 

 till Taihape is reached. 



A small pile of andesitic blocks occurs at Utiku, a few miles south of 

 Taihape, at a point about half a mile from the place wlaere the Hautapu 

 joins the Rangitikei River. This pile lies 1,22-5 ft. above the sea. Till the 

 present year there was no knowledge of andesitic blocks beyond Utiku, 

 which is thirty-nine miles from Ruapehu. 



In February, 1915, 1 discovered a solitary andesitic erratic in the Rangitikei 

 Valley, at the south end of the Mangaweka Railway tunnel, at a height of 

 1,070 ft. above the sea. It lies against the foot of a steep ridge of Tertiary 

 clays, 16 ft. above the lower terrace of the Rangitikei, the surface of which 

 is 175 ft. above the bed of the river. (Plate XIV, fig. 1.) This erratic 

 measures 14 ft. long, 6 ft. wide, and 5-5 ft. high, and its weight is ap- 

 proximately 37 tons. 



The whole of the underside of the block is smoothed and roimded, and 

 scored with deep grooves and striae, the majority of which run parallel 

 with the longer axis of the mass. At one end the striae extend up the 

 sides for about 2 ft. from the bottom. The diagonal striae are numerous, 

 but, as a rule, not so deep as the longitudinal ones. (Plate XIV, fig. 2.) 



This great mass of striated andesite is larger than any block known to 

 occur in the Hautapu Valley. It lies forty-eight miles from its souTce at 

 Ruapehu, and appears to mark the southern limit reached by the ice-borne 

 blocks.* 



* Waterworn boulders of andesite derived from the destruction of the Hautapu 

 moraines are plentiful among the existing river-bed gravels of the Rangitikei River. 



