144 Transactions. 



distinguislied by their fossil-content. The detection of structural disloca- 

 tions is therefore a matter of extrente difficidty. Further, they have been 

 naodified by glaciation, and that agent produces landscape features in 

 valleys which simulate fault-scarps, so that this criterion is very dangerous 

 to apply. However, the marked agreement in grade between the main 

 rivers and their tributaries indicates that any faulting which afiected the 

 main-river valleys and not the tributaries must have dated from a time 

 long antecedent to the glaciation, or that all discordance in grade has been 

 rapidly removed. The apparent conformity of the grade of the tributary 

 with that of the main river is a remarkable feature of the valleys of Canter- 

 bury, and difierentiates them from those of the West Coast Sounds, hanging 

 valleys being quite infrequent except towards the heads of the rivers. It 

 will be apparent, therefore, that this line of investigation does not hold out 

 at present any great hope of furnishing data by which the problem may be 

 solved. 



It may be pointed out that the fractures which really do exist, with the 

 exception of the Esk River and Coleridge Creek occurrences, do not follow 

 the lines as indicated by McKay, and they are divergent from those described 

 for the Kaikoura region by McKay, Hector, and Cotton, which continue 

 into north-eastern Canterbury (see map), and from those recorded in the 

 west of Nelson by Henderson and Morgan. 



There is one further suggestion which may be put forward tentatively 

 to explain the arrangement of the valleys — viz., that their directions were 

 primarily determined by the shape of the land-surface as it emerged from the 

 sea in late Tertiary times. I have shown elsewhere (Trans. N.Z. Inst., 

 vol. 47, 1915, p. 353) that in all probability in late Cretaceous or early 

 Tertiary times the present mountain region of Canterbury had the form 

 of a peneplain; that subsequently this surface was depressed and was 

 covered by a discontinuous veneer of marine sediments; that it was 

 raised at the close of the Tertiary era and during the Quaternary era 

 with some amount of folding and faulting. Now, the streams which cut 

 their beds on this land as it emerged would be consequent on the slope of the 

 covering beds, and as they were removed by erosion our present drainage 

 would become a superimposed drainage. The main valley-directions might 

 then be of great antiquity, while the subordinate ones might be due to 

 fractures of comparatively recent date. They would, therefore, resemble 

 what we should get were the central district of the Wellington Province, 

 between Wanganui and the Ruahine Range, still more elevated than at 

 present, the mantle of sediments removed, and the base of older rocks 

 exposed on which they lie unconformably. The present almost parallel 

 alignment of the rivers would then be pei-petuated on the exposed surface, 

 and would have little relation to the arrangement of the under lynig beds. 

 Even this method of establishment woidd not negative the existence of 

 fractures ; but with the complete removal of the covering beds it would be 

 very difficult indeed, unless the strata exposed were of considerable diversity 

 in lithological character or of fossil-content, to detect the presence of these 

 fractures. 



