THR NEW ZEALAND SOUND BASINS 49 



One would thus naturally expect to get islets remaining after the 

 glacial flood occupation of a wide fiord, since this is the stagnant 

 divergent, as opposed to the rock-basining convergent, canyon stage. 



SUMMARY 



The problem is a physiographic one, since it deals with the origin 

 of present-day rock contours. It is analogous to the study of stream 

 channel and bank contours. 



Southwestern New Zealand was in pre-Tertiary time dissected 

 by subaerial agencies to the early old-age stage. 



In early Tertiary( ?) time this so-developed surface was flexed, 

 attaining a height of about 6,000 feet in the northern portions. Mas- 

 sive residuals of this plateau attained heights of 10,000 feet above 

 sea-level. 



During preglacial times the canyons of this area were determined 

 by stream-action. The channels of these water-courses possessed har- 

 monizing grades. 



Their present contours are the result of marked modification by 

 ice-action during the period of maximum glaciation. 



The Great Ice Age marked a flood in ice-action, while the pres- 

 ent much warmer conditions obtaining in formerlv intensely glaciated 

 regions are significant of a glacial drought. 



The action of this ice-flood is best illustrated by comparing with 

 the stages of an ordinary stream in flood. 



In the case of ordinary • streams, mighty floods along alluvial 

 flats are frequently observed to scoop out holes many feet below these 

 temporary baselevels, especially at points where marked stream 

 convergence occurs. Along either the broads or the bank opposite 

 to that where active cutting is in progress, aggradation also occurs 

 during the very height of the flood. With the rising of the stream 

 above its banks, masses of stagnant back water also are produced, 

 whose principal function is aggradation as opposed to degradation. 



Recession of the flood waters brings about aggradation at the points 

 where maximum excavation was carried on during the flood. Espe- 

 cially does this occur at spots where scooping out below baselevel 

 occurred. 



Similarly for the ice-stream.s of the Glacial Period in New Zealand 



