belt of land about thirty miles long, elongated in a north-north-east 

 and south-south-west direction (and extending an unknown distance 

 farther to the south-south-west beneath the sea). The depth of 

 downwarping that must be assumed is variable, the maximum being 

 perhaps in the neighbourhood of 1,500 ft., or perhaps rather more, 

 where the broadest part of Port Nicholson now is. The width of 

 the strip affected also varies in different parts, but is at least 

 ten miles where Port Nicholson is widest. Both depth and width 

 diminish, though irregularly, to the north-east up the Hutt Valley. 



The movement of downwarping took place comparatively recently. 

 Though the outer coast of the partly drowned area is now approach- 

 ing submaturity of outline, the initial shore-line (after submergence) 

 can still be restored, and it is seen that the change in the normal 

 subaerial land-forms that has taken place since submergence is 

 inappreciable. The surface that was warped and incidentally faulted 

 to produce the depression was therefore like that of the surrounding 

 district to-day maturely dissected, with a somewhat fine texture 

 of dissection and a relief of rather more than 1,000 ft. Such strongly 

 differential movement of a small earth-block in very recent times is 

 unusual even in New Zealand, though it was common enough in 

 somewhat earlier times when the mountain masses were blocked out 

 and the river-courses determined by the movements to which the 

 name " Kaikoura " has been applied. 



The evidence in support of the hypothesis of warping to account 

 for the submergence of the Port Nicholson area is much more con- 

 clusive for the eastern than for the western side of Port Nicholson. 

 In the critical area on the w r estern side ancient strand-] ines do not 

 survive, but have been cut completely away by modern marine erosion. 

 The only positive evidence of warping found there is a progressively 

 more extensive drowning of valleys as the entrance to the harbour 

 is approached ; but there is also weighty negative evidence in the 

 absence of a traceable fault-scarp separating the obviously depressed 

 Port Nicholson area from the high-standing land to the west. 



The evidence on the eastern side is more striking.* It is of 

 three kinds : (i) Uplifted wave-cut platforms (ancient strand-lines) 

 on the outer coast are very strongly tilted endwise towards Port 

 Nicholson (fig. 4) ; (2) there is progressively more extensive drowning 

 of valleys as the harbour-entrance is approached (fig. 4) ; (3) the 

 inferred tilting towards the centre-line of the depression is so strong 

 that it must have considerable effect on the regimen of streams. 

 The larger streams east of the harbour are for the most part parallel 

 to the hinge-line of warping, and, as might thus be expected, are but 

 little affected ; but the valleys of small headwater streams tributary 

 to these and entering them from the west show striking aggradational 

 effects, which can be ascribed only to headward tilting in spite of the 

 steep gradients normal to such streams, even when mature, in this 

 district of strong and fine-textured relief. These effects may be seen 

 well developed in the western branch of the Wainui-o-mata, and in 

 the western tributaries of the Mangaroa (fig. 6).f 



* This evidence is set out more fully in a paper by the present writer 

 entitled " The Warped Land-surface on the Eastern Side of the Port Nichol- 

 son Depression," Trans. N.Z. Inst., vol. 53, pp. 131-43, 1921. 



t Loc. cit., pp. 140-42 ; Geomorphology of New Zealand, p. 238. 



