148 Transactions. 



elevated earth-block now known as the Tararua Range the secondary 

 deformation exercised by far the most potent influence in the determination 

 of the major features of the relief. The marked difference in the drainage- 

 pattern of the Tararua Range and that of the Wellington Peninsula 

 strongly supports this view, and the hilly tract situated to the north-east 

 of Porirua Harbour doubtless forms a transitional area between the north- 

 easterly strongly deformed and the south-westerly less affected surface 

 of the uplifted pre-Miocene peneplain (Bell, 1910, p. 538 ; Henderson, 1911, 

 pp. 312-13). In the transitional area just referred to, the strike of the 

 ancient folds sweeps round and assumes a more easterly direction than it 

 does in the Wellington Peninsula, and intersects the longitudinal ridges 

 and drainage -lines at an angle of approximately 27° ; hence the relief in 

 this locality bears a closer relationship to deformation than to structure, 

 though the influence of the latter may not be wholly wanting. 



The Coast-line. 

 (1.) The Cliff,. 



The outer coast of south-western Wellington is characterized by a 

 continuous line of bold cliffs rising to heights of several hundreds of feet. 

 At and within the entrance to Porirua Harbour the cliffs are still of 

 imposing aspect, but they diminish in height as the distance from the 

 open sea increases. The cliff-cutting has been effected by marine abrasion 

 mainly under the influence of the prevailing north-westerly wind, while 

 the powerful but less-prevalent southerly wind has produced less extensive 

 but similar results, especially on southward-facing sections of the coast- 

 line within the confines of the harbour. 



In itself the cliffed coast-line is a normal feature of marine abrasion, 

 but at the present day it possesses the peculiarity of being beyond the 

 reach of the waves ; in other words, the cliffs do not belong to the present 

 but to a former base-line of marine denudation. 



With the exception of a few places on the outer coast between the South 

 Head of Porirua Harbour and Titahi Bay, and at two or three headlands 

 in the vicinity of Wairaka Ppint, where the sea is again undercutting the 

 high land, the former cliffed coast is separated from the present shore-line 

 by a strip of low-lying ground of a width usually from 5 chains to 10 chains, 

 but in certain situations from a quarter to over half a mile. Along the 

 greater part of its length the low-lying strip at the base of the cliffs is a 

 raised rock platform — an uplifted incipient plain of marine denudation 

 (Plate XXXV, and fig. 2, a) ; the remaining portion — situated principally at 

 the seaward ends of the larger valleys opening into Porirua Harbour near its 

 entrance — has been formed by the progradation of the shore brought about 

 by the deposition of a superabundance of coarse waste which has been 

 drifted down the outer coast and into Porirua Harbour and has been 

 piled up above sea-level, in the first instance by the action of the waves, 

 and raised still farther by the earth-movement responsible for the uplift 

 of the adjacent stretches of shore-platform of wave-planed rock. 



(2.) The Raised Shore- platform, 

 (a.) On the Mainland. 



The raised shore -platform (Plate XXXV, and fig. 2, a) is one of the most 

 interesting, and in some places also the most conspicuous, of the shore- 

 line features of Porirua Harbour and of the neighbouring coast. The earth- 



