600 Transactions. 



the third trial artesian bore on the State farm at Weraroa a rata log 2 ft. 

 in diameter was found 135 ft. below the present surface. An old well- 

 sinker stated that he had found flax-leaves which still retained their green 

 colour beneath 18 ft. of shingle. This well was situated on Section 46 in 

 Levin Borough. 



From its apex to about two miles down its slope the Ohau fan has 

 a fairly regular surface — that is to say, the curve exhibited by a cross- 

 section would be a regular one. Further down its slope, however, its surface 

 is characterized by ridges and hollows, whose strike is parallel to the dip 

 of that surface. In this part the surface-curve, as shown by a cross-section, 

 would be sinuous, though here the fan still retains its hyperbolic contour. 

 The ridges are usually from 5 to 10 chains apart, and, though they seldom 

 have an amplitude exceeding 3 ft., are especially noticeable where a road 

 crosses some of them. 



As shown by the coarseness of some of the transported material, and 

 also by the occurrence of driftwood, the Ohau fan is largely a flood 

 deposit. As material was swept out from the mountain-enclosed valley 

 on to the coastal plain, the river, being more confined to the immediate 

 neighbourhood of its vent, would at first spread that material evenly in 

 every direction. Further out, where spurs were absent and the river had 

 freer play, ridges of deposit would be built up, until it was forced to change: 

 its course. While the river was in this state of oscillation — building up, 

 being deflected when its bed became unstable, and eventually returning 

 to its original position, and repeating the process on different parts of its 

 fan — a slight change in the direction of its flow when near the apex of th(^ 

 /an would usually cause a considerable alteration in the position of that 

 portion of its course situated further down the slope, and as a result the 

 low radiating ridges would there be built up. 



The Ohau River not only deposited shingle and gravel on the Pliocene 

 coastal plain, but it also filled up with the same materials the deep valley 

 it had cut (in the Tertiary epoch) through the rocks of the Tararua Ranges. 

 This deposition of shingle, &c., in the primary valley of the Ohau was simul- 

 taneous with the formation of the fan, the latter being the doAvnward ex- 

 tension of the former. 



When the deposit in the valley had attained its maximum thickness 

 it formed a sloping plain bounded by the hills, and traversed by the Ohau 

 River and its two principal tributaries — the Makahika and the Makaretu. 

 Formerly both these tributary streams joined the main river further up- 

 stream than they do at the present time ; also, the Ohau itself flowed across 

 the shingle plain south-east of, though more or less parallel to, its present 

 channel. 



In shape the hill-enclosed alluvial plain which occupied the Ohau Valley 

 bore a close resemblance to a three-fingered hand. The wrist was repre- 

 sented by the narrow strip, varying from 10 to 15 chains in width and three- 

 quarters of a mile in length, which extended up-stream from the fluviatile 

 vent; the palm of the hand was the widest part of the plain, lying round 

 about the junction of the Ohau and its tributaries ; and the fingers were 

 the upward extensions of tlie shingle-beds in the respective valleys of these 

 rivers. 



While the " valley plain "^ — that is, the plain within the hiU-enclosed 

 part of the Ohau Valley — was approaching completion the Ohau River 

 appears not only to have debouched upon the " plain "' just south of its 

 present channel, but also to have had an alternate coiirse, from its upper 



