LOQ r rdii^actioiis. 



This old ■■ nortli-west " course is what imi}- be termed the '" interme- 

 diate stage " in the recent geological history of the Ohau River. Formerly 

 by the process of aggradation it formed a massive deposit of shingle and 

 gravel, and now by erosion it has excavated a deep valley in that forma- 

 tion. It is hardly likely that these very adverse conditions were abruptly 

 consecutive, but that they were separated by an intermediate stage, which 

 was a period when the river was neither depositmg material nor to any great 

 extent scooping out a well-defined channel. The old " north-west " channel 

 was this " intermediate stage.'" 



Though the shallow '' nortli-west '" valley of the Ohau River eventually 

 attaiiied a width of about a mile and three-quarters, it was at first much 

 narrower. For a reason which will transpire in the sequel, the river — 

 which originally flowed to the sea near and parallel to the present position 

 of Queen Street (Town of Levin) — continually attacked its left bank, causing 

 it to retreat to the vicinity of Kimberley Road. Prior to this lateral erosion 

 by the Ohau River, the streams from the hills a couple of miles south of 

 the fluviatile vent combined and occupied a wide but shallow valley situ- 

 ated along the line of the present Kimberley Road. The stream formed by 

 this union flowed first into the sea, but afterwards into the southern end 

 of Lake Horowhenua, which was thoi from 30 ft. to 40 ft. deeper (and 

 consequently more extensive) than now : and when it had excavated its 

 valley through the sandstone formation to the upper surface of the Ohau 

 fan it filled its valley-bottom with alluvium — clay derived from the hills 

 at its sources. By the lateral erosion just described the Ohau River re- 

 moved the right bank of the " Kimberley Road " valley, tapping it 

 and cutting into the clay alluvium. Though subsequent erosion has 

 removed some of this clay deposit, the remainder can still be seen 

 extending from the intersection of the Arapaepae and Kimberley Roads, 

 through the Weraroa >Stat(! Farm, toward the southern end of Lake 

 Horowhenua. Originating as a flood-plain, it constitutes one of the most 

 fertile portions of the district. 



By the time the Ohau had gained access to the old " Kimberley Road '" 

 valley, however, the latter had been deserted by the stream which formed 

 it. The " Kimberley Road "' stream seems to have been divided from 

 the streams which drained the hills still further south by a low ridge of 

 the soft marine sandstone ; and, having aggraded its bed with the clay 

 alluvium, lateral erosion -commenced, by which means it cut through 

 the dividing- ridge, and allowed itself to bo captured by one of the afore- 

 mentioned neighbouring streams. 



These small watercourses have their sources in the outlying Poroporo 

 Range, in the adjacent Tararua foothills, and in the intervening valley. 

 They flowed round the northern and of the Poroporo Range, entering 

 the sea directly opposite. One of them, the Kuku Stream, afterwards 

 raised its bed by depositing alluvium, and flowed over a low col — 

 situated near the northern end of the outlving range — subsequently cutting 

 the small ravine which it still occupies. 



Though there is ' no direct evidence that the '" Kimberley Road " 

 stream vacated its original valley befori; the Ohau had gained access to 

 it, for two reasons such is believed to have been the case. One is 

 that the clay alluvium has not been channelled in the manner it probably 

 would have been had the stream flowed into the Ohau ; and the other, 

 and more important, is that had the deviation not taken place the original 



