-GEOLOGY 



Aet. LXVIII. — On the Formation of Lake Wakatipu. By William Stuakt. 



\Read before the Southland Institute, Wth August, 1881.] 

 The Wakatipu Lake is deepest about half way between its two ends, near 

 the Queenstown bend. The depth is very great, probably the bottom is 

 below sea-level, at any rate it is below the level of the Waimea and Dipton 

 Plains. During occasional visits to this lake, I have been "exercised " to 

 use an old theological expression) to account for this. I know that some 

 have tried to explain it by the theory that the lake bottom had been scooped 

 out to great depth by glacier action. But this was difficult to imagine, 

 Having had occasion during the last twelve months to visit the locality, I 

 carefully examined the country, and came to the conclusion that, whatever 

 may be the case with the neighbouring lakes, the Wakatipu has been 

 formed in much the same way as several of the lakes on the southern side 

 of the Alps in Europe — namely, by the subsidence of the great mountain 

 chain on the side of which it lies. 



That the Wakatipu country has been subject to upheaval and subsidence 

 is clear enough, but the mode of the last subsidence is not so clear. At first 

 sight it would appear, to judge from the plains on the east side of the 

 Southern Alps, and from the fiords on the west (these latter being mountain 

 valleys into which the sea has come), that the island had risen gently on one 

 side of the central chain (as an axis), and had subsided heavily on the other, 

 but a closer examination, I think, will show that this is not what happened. 

 It looks rather as if the island — at any rate this end of it — had gradually 

 sunk as from a hinge from the present east coast line, or more probably 

 from a line far to seaward beyond it. That this end of the island did subside 

 in the manner I describe, is proved, I think, by the existence of the fiords 

 and the comparative shallowness of the sea on the west coast, and by the fact 

 that the seaward moss (which is now gradually rising) shows the remains 

 close to the surface of a submerged forest destroyed in a comparatively recent 

 time. A subsidence in this way would be greatest furthest from the hinge, 

 and least near it — the sea would consequently come over a fringe of land, 

 and be shallow on the east, and would cover much land deeply on the west. 



Now the alpine range, before the subsidence I am speaking of, un- 

 doubtedly stood at a much higher elevation than at present, at least 6,000, 

 more hkely 10,000 feet, as the deep fiords on the west side of Fioj»d County 



