76 Transactions. 



cessation of marine deposition in these parts is, I think, a good reason for 

 considering the Oamaruian a distinct geological unit in the chronological 

 succession of the Tertiary formations. 



A cessation of deposition, or even an abrupt faunal change, is merely 

 the expression of a geographical change. The absence of marine Pliocene 

 deposits in the north and south of New Zealand must be regarded as a 

 consequence of a differential elevation that raised the sea-floor in these 

 parts till it became dry land, but did not affect the central region till late in 

 the Pliocene. 



At the close of the Pliocene the differential uplift became general 

 throughout the length and breadth of New Zealand, the movement being 

 more rapid along the axis of the main chains than towards the coasts to 

 the east and west. The unequal upward movement raised the marginal 

 cover of Tertiary strata high up on the flanks of the upraised axial chains, 

 and at the same time subjected the rocks composing these chains to stresses 

 that found relief by the formation of powerful faults. The major faults 

 run more or less parallel with the trend of the folded chains. Thus in 

 western Southland and in Otago they run north and south ; in Canterbury, 

 Marlborough, Welbngton, Hawke's Bay, and south Auckland, north-east 

 and south-west ; in eastern Southland, north Nelson, and north Auckland, 

 north-west and south-east. 



The ancient peneplain, Tahora, which for a hundred thousand genera- 

 tions had exercised a powerful influence on the arrangement and distribution 

 of the younger formations, now became deeply dissected, and for the most 

 part almost obliterated, by the intense pluvial and glacial erosion of the 

 Pleistocene period. In almost all cases the lines of dissection followed fault- 

 planes, along which the rocks were, as a rule, shattered, and hence incapable 

 of offering an effective resistance to the turbulent mountain-streams and 

 the ponderous advance of the Pleistocene ice -sheet. The dissection of the 

 uplifted peneplain was preceded by the removal from its surface of the 

 covering strata, except along the coast and in the trough-faulted mountain- 

 basins, where they were in some measure protected from the full activities 

 of subaerial denudation. 



The Pliocene uplift, elsewhere called the Ruahine movement,* gave the 

 finishing-touches to the structure of New Zealand. The crustal disloca- 

 tions and faultings which accompanied it determined the lines of the great 

 trunk rivers, already well established in their courses when the Pleistocene 

 refrigeration began. The Pleistocene glaciers descending from the alpine 

 chains ploughed out and deepened the valleys, smoothed the contours of 

 the mountain-slopes, and wore down to rounded hummocks the rocky 

 ridges lying in their path. Before their final retreat they piled up vast 

 moraines that will always remain as imperishable monuments of the iron 

 grip in which iu the near past the great Ice King held this now sunny 

 land. 



* See head of p. 67 of this volume. 



