536 Transactions. 



The peneplain, as its name implies, was not absolutely a plain, but 

 doubtless owing either to original greater resistance in composition, or 

 possibly of favourable position free from attack by erosive agencies, a few 

 hills remained above the general denuded surface. 



Following the peneptanation of the land, the land-surface was again 

 elevated, or relatively elevated, with regard to the sea. Possibly as a par- 

 tial expression of this elevation, or since that event, came the faulting move- 

 ments which separated the several blocks of the peneplain to the east of 

 the harbour, tilted the bTock to the west thereof, and formed the original 

 depression now occupied by Wellington Harbour. The depression in the 

 beginning seems to have been a graben, somewhat complex in nature, which 

 extended from the sea up the Hutt Valley. It is probable that at first the 

 down-faulted trough was not entirely beneath the sea, but was occupied 

 by a large stream, the antecedent of the present Hutt Kiver. The erosive 

 influence of this ancient stream profoundly influenced the contours of the 

 original depression before renewed subsidence lowered at least the outer 

 part of the graben beneath the sea. 



Outline op Hills behind Wkllington. 



The complicated graben of which the harbour and the lower Hutt 

 Valley are the expressions by no means represents a single depressed block, 

 but consists of several parallel and transverse blocks, not all of which have 

 settled down equally either transversely or longitudinally. Thus the low- 

 Iving areas of country between Lyall Bay and Evans Bay, and between 

 Island Bay and Lambton Harbour, have apparently not subsided to the 

 same depth as the floor of the main body of the harbour, though it is not 

 improbable that both these areas were either originally below sea-level 

 or at least occupied a lower altitude than at present, their height above 

 sea-level and general surface-area being increased by wind-blown sands. 

 In the same Avay it seems evident that the Seatoun Hills, the Kilbirnie 

 Hills, Somes Island, and Ward Island represent e'ther whole blocks or 

 portions of blocks of the peneplain Avhich were after the time of major fault- 

 ing much higher, and now owe their reduced position and more mature 

 sculpturing, as compared with the surface of the peneplain to the west 

 and of the various blocks of that surface to the east, to the more rapid 

 denudation consequent on their isolated and exposed positions. 



Since the final depression of the graben beneath the sea the surface of 

 the land has been much influenced by erosive action — marine, fluviatile, 

 and subaerial. Thus the generally flat surface of the blocks of the pene- 

 plain has been dissected by numerous streams into ridge and valley, so that 

 the plain appearance remains only in a few places, such as near Karori and 

 near Johnsonville ; and the isolated horsts, such as the Kilbirnie Hills, 

 have been worn into well-rounded ridges with slopes completely cloaked 

 ■with the deposits of rock-decay. 



Exactly how far the original depression due to faulting extended up the 

 Hutt Valley is not known, but it is very probable that its apparent area 

 has been much increased bv the erosive influence of the Hutt Kiver. 



