C. A. Cotton — Bloch Mountains in New Zealand. 291 



average slope of grey wacke fault scarps is nearly twice as steep 

 as that of schist scarps. Like the schist fault scarps, though 

 generally not deeply dissected, these may be described as sub- 

 niature or mature with graded slopes. The difference in 

 steepness between the schist and greywacke scarps is to be 

 ascribed, therefore, to the much steeper gradient which in the 

 greywacke blocks represents a condition of equilibrium after 

 the first rush of scarp destruction by crumbling and slumping 

 initiated by the deformation. 



In low scarps (up to about 1,000 feet) the average slope of 

 the salients (scarcely to be dignified by the term spurs) is about 

 40°, and that of the intervening reentrants somewhat less. 

 Definite sharp-edged facets are not found, the salients being 

 general]}^ of even slope and broadly convex as a result of grad- 

 ing of the slopes by soil creep. Instead of ravines the reen- 

 trants are usually funnel-shaped shoots that merely scallop the 

 edge of the upland surface. They are occupied by streams 

 not of water but of angular fragments of rock. Such a scarp 

 is found in the front of the southern end of the Hunter's Hills 

 block in Southern Canterbury (fig. 8), and a much higher one 

 forms the western slope of the St. Bathans block, the shallow- 

 ness of the dissection of the front of which is due to the strong 

 backward tilt of the block. 



In high scarps which do not conform to this extreme type, 

 mature dissection has been effected by steep-grade permanent 

 streams whose heads penetrate only a short distance back into 

 the highland plateau. Of this nature are the Hawkdun and 

 Kakanui fault scarps (figs. 18, 20, and 26). 



6. The Floors of the Central Otago Depressions. 



In general the depressions contain no great accumulations of 

 alluvium as a result of postdeformational aggradation. The 

 vast quantity of waste resulting from the stripping of the 

 overmass from the uplands and its erosion in the lowlands, as 

 well as that derived from the erosion of portions of the under - 

 mass, has been removed in the course of ages by streams, many 

 of which seem puny and almost powerless. In those large 

 areas in which the covering strata extend below local base- 

 levels and have thus escaped complete removal, planation of 

 their surface is far advanced. This is particularly true of the 

 southern parts of the Ida Yalley and Maniototo depressions, 

 floored by the level valley plains of the Pool Burn and the 

 Upper Taieri River. 



The northern portions of the Ida Yalley and Maniototo 

 depressions and of the Manuherikia depression, w^hich are prac- 

 tically continuous, may be described as a local peneplain, the 

 erosion of which has been lately revived several times. The 

 upper courses of the streams of the northern part of the Manio- 



