president's address- -section c. 113 



Cromwell, in Wiestern Otago, and there can be little doubt that, 

 as suggested by Dobson (1865), McKay (1892), and Andrews 

 (1911), tectonic depression must have contributed very largely to 

 the foTuiation of the lakes of the South Island of New Zealand. 

 Indeed; as observed previously, the disposition of the covering 

 rocks about Te Anau gives proof of the fcectonio origin of that 

 depression. So, also, in the region of the Marlborough Sounds, 

 though the softer schists have permitted a much greater rounding 

 of the eurface than in the harder gneisses of Fiordland, the in- 

 faulting of Nctccene coal-measures at Picton at the head of Queen 

 Charlotte Sound (McKay 1882) confirms the impression drawn 

 from the reticulate character of the drainage of north-eastern Marl- 

 borough, that the drainage-system is essentially de^pendent upon 

 the crustal structure, being either guided by tectonic depressions, 

 or eroded in wide zones of fault-breccia such as were described by 

 Henderson and Ongley (1920), or follow joint-planes (Webb, 

 1910).* In Canterbury the conditicais are somewhat similar. 

 Speight (1916) has stated that here certain subordinate valleys 

 show indications that their directions are dependent upon the 

 deformation of the strata, though the main valleys have not fur- 

 nished positive evidence of this, but may be dependent on such a 

 cause, as their reticulate arrangement suggests. The chief difficulty 

 in detecting fault-lines in the mountain region of Canterbury is 

 the extremely monotonous character of the rocks. Where, how- 

 ever, fractures are brought into evidence by the presence of in- 

 faulted outliers of the covering strata, conformity with the direc- 

 tion of the adjacent valleys is clear (e.r/., Speight, 1917). Near the 

 heads of the valleys, where the control of slope over the stream - 

 course is dominant, departures frcm the structural lines are the 

 most marked. In general, the valleys of Canterbury follow a 

 north-eaeterlv and a north-westerly trend, and Cotton shows that 

 the same directions hold in Otago. Between these provinces is 

 the Waitaki Eiver flowing to the bouth-east in its middle and 

 lower course, where it is " guided by a linear tectonic depression, 

 irregularly bounded by the fault-scarps and back-slopes of a com- 

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

 of covering strata are preserved." (Cotton, 1917, citing Marshall, 

 1915.) The chief tributary of the Waitaki, the Hakataramea, oc- 

 cupies a fault-angle depression elongated in a north-easterly direc- 

 tion almost perpendicular to that of the Waitaki. 



To add to the many features of interest in connexion with the 

 evolution of the present topography, we must notice that great 

 differences of features result from the wide variety of climatic 

 conditions under which the denudation of fault blocks has taken 

 place. The effects of normal pluvial erosion need not be particu- 

 larized, but in the central parts of Otago and Southland, the 



* Tlie fundamental difference between the tectonic and eroded valleys, though sometimes 

 overlooked, has been clearly indicated by D. W. .Johnson (1915). 



