THE NEW ZEALAND SOUND BASINS 



39 



ting curves) will show truncation on certain sides only. Fig. 8 

 illustrates this well. As the ice gathers strength, it will possibly 

 surmount the great canyon walls, and actually flow over the old, 

 flexed upland. This stage may be considered the period of maxi- 

 mum ice-flooding. After the almost complete truncation of spurs 

 in softer rocks, slopes of moderate batter will be induced in the 

 canyon sides, as they will be too weak to resist the lateral thrusts 



Fig. 14. — Sutherland Falls, 1,904 feet high, from a hanging valley which is 

 mature and 2,500 to 3,000 feet deep. Upper Arthur River. Note the majestic wall 

 and notch through which stream comes. Here two deep valleys converge to form 

 Arthur River. 



from the swiftly moving glacier. Deep holes will also be plowed 

 in the bottom rocks to great depths below local baselevels. But in 

 the narrower canyons of the dense crystallines, as around Milford 

 Sound, especially where the steep canyons are from 5,000 to 6,000 

 feet deep, and where marked convergence of valleys occurs, the 

 results will be marvelous. The resultant ice-velocity is much 

 increased as the converging masses are forced into a deep valley 

 only slightly broader than either of its tributaries. The spurs are 

 ripped off, but the resulting massive and aligned walls present great 



