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Transactions. 



theory in explanation of it (pp. 261-62). It was pointed out that the 

 slope descending to Port Nicholson is maturely dissected, and that the only 

 facet-like forms and blunt-endecl spurs more or less in line occur where 

 cliffing by marine erosion has been recently in progress, and this slope as 

 a whole was ascribed without hesitation to the work of normal erosion 

 guided by structure, it being an erosion-scarp along the outcrop of a 

 resistant highly-inclined stratum. 



It may be added that the eastern side of the harbour is now distinctly 

 a shore-line of submergence (Plate XXIX, fig. 1) modified by marine 

 erosion, especially at the southern end, where waves driven into the harbour- 

 entrance by southerly winds still retain considerable energy and have cut 

 a continuous line of cliffs with a height in places of 300 ft. The embay- 

 ments produced by the submergence are small, but this is because of the 



steep declivities of the drowned 

 ravines which dissect the erosion- 

 scarp. Similar embayments, 

 filled with alluvium, are present 

 farther north-east along the edge 

 of the Hutt River delta, which 

 partly fills the Port Nicholson de- 

 pression (Plate XXXIII, fig. 1), 

 and also still farther north-east, 

 where, the depression widens again 

 after a constriction is passed, 

 and is occupied by a basin-plain 

 in which lie Trentham and Upper 

 Hutt (Plate XXXIII, fig. 2). 



The coincidence of the trend 

 of the erosion-scarp forming this 

 eastern shore-line, and also of 

 nearly all the major drainage- 

 lines in the district, with the 

 strike of the folded rocks, suggests 

 not only that the features are 

 subsequent, but also that they 

 are guided bv an alternation of 

 weak and resistant beds in the 

 highly-inclined series of grey- 

 wackes and argillites forming the 

 bed-rock of the district. The 

 contrast between the weak and 

 resistant zones appears to be due in reality to the relative freedom from 

 joints and planes of shearing in the rocks of the latter, and to the jointed, 

 sheared, and sometimes completely crushed condition of the former, which 

 are perhaps best termed " shatter-belts." These belts, however, with one 

 notable exception— the line of the Wellington fault (Cotton, 1914) — are 

 parallel with the strike, and appear to be the result of thrust-faulting which 

 occurred as an accompaniment of the folding of the strata (post-Hokonui 

 orogeny). (The positions of several fault-zones, or shatter-belts, in the 

 Wellington Peninsula, west of the depression, were indicated by Broad- 

 gate, 1916.) Thus the ridge which bounds Port Nicholson and the Hutt 

 Valley on the south-east, along with the straight and parallel valleys of 

 the Mangaroa Stream (a tributary of the Hutt River) and the Wainui- 

 o-mata and Orongorongo Rivers, and the ridges of the Rimutaka Range, 



Fig. 1. — Locality map of the Port Nicholson 

 area, New Zealand. 



