Speight. — Geology of the West Coast Sounds. 257 



of tlie Waiau River and the east side of Lake Te Anau, and may be pro- 

 longed down the HoUyford River. If there is anything in the idea that 

 the general orientation of the valleys depends on fracture-lines, it may 

 have been associated with the movement of the earth's crust. The general 

 even contour of the coast-line on the west and south of the area is remi- 

 niscent of southern Norway, and may be the result of fracture, and the 

 settling of an area in the ocean-floor. This has been referred to previously 

 by the present author in a short paper on a " Hornblende-andesite from 

 the Solanders."* 



The other explanation of the orientation is that the valleys were origin- 

 ally consequent on the shape of a former land-surface. This would result 

 if the land to the west of Lake Te Anau had been raised in the form of an 

 oval ridge with its chief axis riuming north-east and south-west. The first 

 drainage-lines established would then be north-west and south-east, across 

 the general strike of the beds, which have a general north-westerly dip. 

 Subsequent streams would take a line approximately at right angles, or 

 parallel to the strike, and, by the processes of absorbing neighbours and 

 extension of their basins, might become the most important drainage- 

 directions. This may, perhaps, be a more satisfactory explanation than 

 that depending on fracture, and it is possible, of course, that both causes 

 may have been present. But if the valley-directions depend on fracture- 

 lines they must date from a time anterior to the glaciation, and cannot be 

 intimately connected with movements that are subsequent to it. 



The most interesting physiographical questions are those connected 

 with the results of glacier erosion. That glaciers do erode their beds deeply 

 seems almost certain when the landscape-forms of the region are considered, 

 and the present author agrees with Sir James Hector when he attributes 

 most of the pecuhar features to the overdeepening of the main valleys by 

 powerful glacier erosion, as compared with the feebler erosion that went 

 on in tributary valleys when glaciers were smaller. This will explain the 

 hanging valleys, the waterfalls, the truncated and semi-truncated spm's, 

 the alignment of the valley-walls, and the U-shaped cross-section and 

 the longitudinal section of the Sounds, as well as the rock-bound lake- 

 basins — i.e., the pot-holes of a glacier stream, quite analogous to the pot- 

 holes of a river. These points have been fully dealt with by Andrews (1, 2). 



The formation of lake-basins by scouring action analogous to the pot- 

 holes of a river must result in some cases. It seems hard to explain the 

 formation of the small rock-bound lakes at the head of George Sound on 

 any other assumption. A striking illustration of the efficacy of this action 

 is furnished by the Rakaia River, in Canterbury. A great glacier flowed 

 down the valley, and part turned at right a.ngles over a low saddle in the 

 direction of Lake Heron. At the point of turning is a well-marked trun- 

 cated spur with semi-detached knob, and below it a basin nearly half a mile 

 across, smoothed and rounded on the inside, the direction of scouring being 

 clearly circular and horizontal. This was evidently a whirlpool in the ice 

 stream, formed at just such a place as that at which a whirlpool would 

 form in a river, and no doubt foimed in an analogous way. This is a 

 pecuhar case, which I shall deal with more fully in a subsequent paper, 

 but it illustrates the power of erosion possessed by glacier-ice. It seems 

 likely that many small rock-bound lakes in glaciated coimtry, especially 

 those at lower levels, may arise in this way. 



* Trans. N.Z. Inst., vol. xli, p. 52. 

 9— Trans. 



