44 Transactions. 



McKay was correct in suggesting (1884, p. 62) that considerable areas 

 of his Pareora gravels and clays underlay the moraine which covered a 

 considerable area of the plains, seeing that remnants of this deposit have 

 now been located near their upper margin. Up to the present the valley 

 of the Tasmai River has yielded no positive evidence of the existence of 

 these beds, but the character of the slopes about Braemar is such that 

 similar Tertiaries might be located beneath them. 



There is thus direct evidence of the structural origin of the basin, 

 apart from that suggested by its form ; but the special point left to consider 

 is the date at which it took on this form — that is, whether it antedates or 

 postdates the time of deposition of the beds contained therein. 



Hutton (1875, p. 64) was firmly convinced that the areas were basin- 

 shaped before the deposits were laid down in them — that is, they were of 

 pre-Pliocene origin — just as he maintained that the Canterbury intermounts 

 were pre-Tertiarv (1885, p. 91). In this he was followed bv McKay (1884. 

 pp. 76-81) and by Park (1905, p. 523 ; 1906, p. 9 ; 1908, pp.* 17 el seq.), who 

 restated his position in his Geology of New Zealand (1910, pp. 141-44). The 

 latter evidently dates the formation of his block-mountain system of Otago 

 and the Wharekuri basin to pre-Pliocene times, although he gives in 

 numerous places instances of the beds concerned having been involved in 

 faults and other deformations which may well have originated or have been 

 attendant features of the formation of the basins. 



On the other hand, Marshall (1915, pp. 380-81) has expressed the opinion 

 that some of the basins, such as that at Wharekuri, were formed after the 

 deposition of the Tertiary sediments, and that the landscape as it now exists 

 has no resemblance whatsoever to the form of the surface when deposition 

 was going on. This opinion has been strongly supported by Cotton (1916, 

 pp. 316-17, and 1917, pp. 249 el seq.), who points out that the evidence for 

 the basins being filled with lacustrine sediments is extremely slight, and 

 that they were subjected to deformational movements after deposition, 

 and that the dominant surface-features result from the fanlting-down of 

 blocks covered with a non-resistant veneer of Tertiary sediments which 

 were preserved in the low-lying basins resulting from this faulting, whereas 

 on the higher elevations it was completely or almost completely removed 

 by erosive agents. In this paper, too, he endorses the statement that the 

 upper course of the Waitaki River occupies a broad tectonic depression, 

 and apparently accepts Kitson and Thiele's explanation of its origin, 

 although this conflicts somewhat with his explanation of the origin of the 

 basins of Central Otago. 



The most important piece of geological evidence, apart from the physio- 

 graphical, is that furnished by the character of the deposits themselves. 

 There is a widespread absence of coarse sediments in the basal beds of the 

 basin — sediments suggesting a, mature topography and the absence of high 

 land in the vicinity of the area of deposit ; and if this contention is correct 

 the landscape must have been entirely different from what it is now. It 

 is inconceivable that sediments could have been laid down in basin-shaped 

 hollows as at present existing without, in some parts of the area, coarse 

 conglomerates forming an important element in the lower members of the 

 series. Again, the presence of numerous quartz pebbles in conglomerates 

 like those in the Macaulay Valley, evidently strangers to the district, cannot 

 be eashV explained tmless the drainage directions were considerably different 

 at the time of deposition from what they are at present. These- geological 

 features are not explained on the hypothesis that the " lake-basins " were 

 formed before they were loaded up with sediments. 



