257 



miles, of which seven miles are at 16 feet per mile, and the last nine miles at 

 96 feet per mile, it accords with the gradual recession of the glacier, and the 

 deposit of moraines in the same order. It must also be noted that as the 

 glacier retired, more and more of the lake bottom from the south end would 

 be released from the grinding action, while the operation would still be in 

 force in the other parts of the lake. 



As already mentioned, there are no soundings of the other lakes available 

 in this investigation. But the very complete Admiralty survey of the West 

 Coast affords a comparison with each of the sounds there. In all of them 

 there is this peculiarity — that, while they are from 700 feet to upwards of 

 1200 feet deep, in no case is their entrance to the ocean deeper than 350 feet 

 — so that if the West Coast were raised 300 or 350 feet, the sounds wovdd 

 become lakes varying in depth from 400 feet to 900 feet. 



If glacial action is sufficient to have excavated the sounds on the West 

 Coast, it may be urged in objection — Why should the glaciers scoop out 

 deeper basins in the hard rock of the West Coast, than in the comparatively 

 less hard rock of the Wakatipu Basin 1 



This objection might be disposed of by assuming that the West Coast has 

 b6en gradually sinking. But adhering to the mechanical principle, the objection 

 may be met by considering that the slopes on the western side of the moun- 

 tains are more steep than on the eastern side, and therefore the glaciers would 

 act more efficiently, having a greater vertical longitudinal pressure, and by the 

 same difference a greater friction. Then in. regard to the harder rock. This 

 objection woxild be of great moment if the ice were the rubbing power ; but it 

 is only the frame or machine in which the chips of rock are set to do the 

 grooving. In hard rock these chips will be part of the rock itself, so that the dif- 

 ference as to the nature of the rock is not so great an objection as at first appears. 



The difference in the depth of the sounds seems to have a relation to tlie 

 heights of the surrounding mountains, as thoiigh tlie excavating process was most 

 active where the greatest snow field existed to feed the glacier, and the greatest 

 pressure to urge it forward. The lake at Martin's Bay [Lake McKerrow] is the 

 only lake of any note on the west side. It may be cited as an illustration of the 

 excavation or basin bearing a relation to the efficiency of the glacial action. 

 The Hollyford Yalley, in which this glacier would lie, is the largest valley on 

 the west side of Otago. It is surrounded by very high mountains, which 

 would create and maintain a large glacier. Under these conditions, not only 

 has a basin been excavated, but sufficient moraine matter has been carried 

 forward to dam back the sea, and so a lake has been formed, and not a sound 



In a paper by Dr. Hector,* in Trmis. N. Z. Institute, Yol. ii., pp. 373-4, 



* The author appears to hold the view, now generally abandoned, that the motion of 

 the lower and horizontal part of a glacier is due to vis a fergo. In other respects he 



2 L 



