394 Transactions. — Geology. 



On the Formation of Lake Wahatipu. Bj Capt. Hutton. 



The formation of Lake Wakatipu has been ascribed by Dr. Hector ("Mining 

 in New Zealand," Trans. N.Z. Inst., II., p. 374) to unequal subsidence, while 

 Mr. J. McKerrow {Trans. N.Z. Inst., III., p. 256*) ascribes it to the erosive 

 action of a former glacier, in accordance with the theory put forward by my 

 esteemed friend and instructor Professor Ramsay, which theory he has, in my 

 opinion, reduced to a demonstration such as is rarely seen in geological 

 inquiries. I need therefore scarcely say that I agree with Mr. McKerrow as 

 to the glacier origin of Lake Wakatipu, but in order to establish ray opinion 

 I will examine what would be the results that an acceptance of the unequal 

 subsidence theory would lead us to. 



Lake Wakatipu is a rock-bound basin, lying in a nearly north and south 

 direction, with a sharp east and west deflection in the middle ; consequently, 

 if it has been formed by unequal subsidence, this subsidence must have been 

 most in a northerly direction, for if it had been in a westerly direction the end 

 of the lake would have been at Queenstown. Of course, a southerly elevation 

 would produce the same effect as a northerly depression. Now the deepest 

 part of Lake Wakatipu is 1,400 feet, off Collins Bay, about 16 miles north of 

 Kingston (McKerrow, I.e., p. 254), consequently, to change a horizontal surface 

 to one having this slope, Kingston must have been elevated 1,400 feet more 

 than Collins Bay, and this would give an elevation to the coast of Southland 

 of 8,400 feet, and to Stewart Island an elevation of about 11,000 feet ; or, if 

 the lake was caused by depression, Collins Bay must have been depressed 1,400 

 feet more than Kingston, which would give a depression to Jackson Bay on 

 the west coast, due north of Kingston, of 9,800 feet. These are the very least 

 movements that can account for the phenomena, for if Kingston was not the 

 axis of the movements, or if the movements had taken place in any other 

 direction than that of the length of the lake, they would have to be immensely 

 increased in order to bring about the same result. But most of the sounds, 

 the origin of which Dr. Hector also ascribes to the same movements, are south 

 of Lake Wakatipu, and are therefore situated in that part which would have 

 undergone the least depression, so that they are just where they ought not to 

 be if this unequal depression has occurred over the whole country. Lake 

 Monowai also requires that the depression should have been towards the south 

 instead of the north. If also movements on such an extensive scale had taken 

 place since the pleistocene period, the river system of Otago would be certain 



* In this paper IMr. McKerrow j)oints out, I believe for the first time, the very im- 

 portant fact that the constrained flexure of a solid body like ice, when passing from one 

 angle of inclination to another, would greatly increase the friction at this particular point. 



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