268 C. A. Cotton — Block Mountains in New Zealand. 



been convinced that it was evidence of deformation. Gordon 

 mentioned an interstratilied leaf bed at St. Bathans " at about 

 the same inclination as the face of the schist rock against 

 which the quartz drift is lying" (p. 119), and appears, however, 

 to have regarded the covering strata as local fiuviatile deposits, 

 and the predeformational relief as strong. 



Park in 1906, 1908, and 1910 described the ranges as block 

 mountains and recognized that the initial forms roughed out 

 by the deforming movements still determine the general forms 

 of many of the mountains of Otago. He pointed out that the 

 upland surfaces in Central and eastern Otago are portions of a 

 dislocated plain of erosion which he termed a peneplain. This 

 plateau had been recognized by Andrews (1905, p. 192), and 

 mentioned also by Marshall (?1905, p. 103), both of whom 

 regarded it as a peneplain ; but neither of these authors appears 

 to have understood the manner in w^iich the surface had been 

 dislocated, both regarding the relief of Central Otago as the 

 work of erosion. With regard to the origin and filling of the 

 so-called lake basins, Park favored an explanation involving con- 

 temporaneous deformation along lines of fault. He regarded 

 the whole of the cover that had been affected by the deforma- 

 tion as lacustrine and, therefore, younger than the initiation 

 of deformation. 



Though Park (1910) has described the South Island as cov- 

 ered by an ice sheet in the Pleistocene glacial period, he has 

 not specifically appealed to glacial sculpture to account for the 

 erosional features of the Otago block mountains, merely credit- 

 ing the excavation of the Dunstan gorge to the work of ice 

 (1906), and describing some morainic accumulations in the 

 adjacent portion of the Manuherikia depression. The Dun- 

 stan gorge was also described as guided by a fault line (1908). 



The writer's hypothesis involves planation, sedimentation, 

 and deformation followed by a period of erosion, during which 

 large areas of the planed undermass have been reexposed by 

 stripping of the cover. 



2. Structure. 



For a great part of its length, the Otago Central Railway fol- 

 lows a chain of broad tectonic depressions and to these the 

 road system of Central Otago is also mainly confined. It is in 

 connection with this chain of depressions that the salient 

 " block " features occur that present the closest analogy with 

 the block mountains described in other parts of the world (see 

 figs. 11 and 13). 



Throughout a great part of the area the undermass consists 

 of metamorphic rocks irregularly but not generally closely 

 folded, and moderately though not highly resistant. To the 



