Cotton. — Warped Land-surface at Port Nicholson. 131 



Art. XVI. — The Warped, Land-surface on the South-eastern Side of the 

 Port Nicholson Depression, Wellington, N.Z. 



By C. A. Cotton, D.Sc, F.N. Z.Inst., Victoria University College, 



Wellington. 



[Read before the Neiv Zealand Science Congress, Palmerston North, 28th January, 1921 ; 

 received by Editor, 1st February, 1921 ; issued separately, 4th July, 1921.] 



Plates XXIX-XXXIV. 



Contents. p age 



The Problem 



The South-eastern Boundary of the Depression 



General Tectonic Features of the Depression 

 The Evidence 



Summary 



Tilted Coastal Platforms 



The Platforms farther West 



Platforms of the Eastern Side tilted towards the Depression 136 



Evidence from Drowned Valleys 

 Evidence from Regraded River-valleys 



Appendix : The Problem of the Turakirae Coastal Plain 



List of Papers referred to 



The Problem. 



131 

 131 

 133 

 134 

 134 

 135 

 13.5 



138 

 140 

 142 

 143 



In 1912 the writer described Port Nicholson, the harbour of Wellington, 

 as occupying an area of subsidence with somewhat indefinite boundaries, 

 and later, in 1918, in a brief account of the coastal features of New Zealand, 

 termed it " a locally down warped and embayed area." It had previously 

 been described by Bell (1910) as a complex graben. The present article 

 is concerned with evidence of warping on the south-eastern side of this 

 area, which is here termed the ' Port Nicholson depression " —warping 

 that is of interest not only from a geological point of view, because of its 

 sharpness, but also from the viewpoint of geography, since it forms a 

 boundary of one of the finest natural harbours in the world (fig. 1). 



The South-eastern Boundary of the Depression. 



Bell appears to have regarded the eastern boundary of the Port Nichol- 

 son depression as a fault-scarp, and eastward of the harbour — between it 

 and the Rimutaka Range — his map and profile indicate the presence of a 

 narrow fault-bounded block standing lower than the block forming. that 

 range (1910, pp. 537, 539). No mention of tilting of this step-like inter- 

 mediate block was, however, made by him. 



The writer, in 1912, inclined to the belief that either the original 

 boundaries of the subsided block were flexures rather than faults, or, on 

 the other hand, the original subsidence had taken place so long ago that 

 topographic evidence of faulting had been destroyed. The distinct and 

 prominent scarp of the Wellington fault along the north-west side of the 

 harbour was regarded as of much more recent origin than the depression 

 as a whole, which, though it must have been deepened, was not initiated 

 by the late insinking along this fault. Field-work having been mainly 

 confined to the area on the western side of Port Nicholson, the question 

 of the eastern, or south-eastern, boundary of the whole depression was 

 then left open (p. 262), but reasons were given for rejecting the fault-scarp 



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