C. A, Cotton— Block Mountains in New Zealand. 285 



land plateau between the Dunstan block and the Old Man 

 Eange to the southwest. It may, therefore, be classed provi- 

 sionally as consequent. The same orio^in may be assigned to 

 the gorge in which the Ckitha leaves the Manuherikia depres- 

 sion in a southerly direction. Farther downstream the river 

 traverses a succession of narrow tectonic depressions. The 

 Clutha river system may, therefore, be regarded as almost 

 entirely consequent. 



The Mataura and Oreti also flow generally in broad tectonic 

 depressions and must be classed as generally consequent. 



Fig. 23. 



Fig. 23. View looking southeastward down the Dunstan Gorge, by way 

 of which the Clutha River breaks into the Central Otago chain of depressions 

 after leaving the Upper Clutha chain. 



The Waitalci River System. — The great Waitaki Eiver 

 occupies in its upper course a broad tectonic depression, the 

 details though not the general form of which have been modi- 

 fled by glacial action."^ In its middle and lower course the 

 Waitaki is guided by a linear tectonic depression irregularly 

 bounded by the fault scarps and back slopes of a complex of 

 blocks in the bottom of which some low-lying remnants of 

 covering strata are preserved (Marshall, 1915). 



The Waitaki Eiver is thus probably wholly consequent on 

 the deformation. It follows a complex graben along the north- 



*Kitson and Thiele (1910) describe the Waitaki Basin as "due to pre- 

 glacial erosion, faulting, with probably some warping, modified by glacial 

 action" (p. 551). 



