HiGG-iNSON. — On Floods in Lake Districts. 183 



about 100 ° from the axis of its course, about eighteen miles from where 

 generated, in order to pass round the first of these. This, therefore, is not 

 probable. The result would be, I think, different, and would possibly account 

 for the j)ulsations noticed. 



We will presume that this large body of water in passing into the lake 

 created, while endeavouring to find its level, a gentle swell or wave which, 

 from the conformation of the lake, could only be propelled in the direction 

 of its length ; this, upon arriving at the first bend would impinge against 

 the southern shore, and instead of passing round the bend would be reflected 

 back towards the northern side of the lake, and so create an oscillating wave 

 which, upon reaching Queenstown Bay, would rise and fall at intervals 

 corresponding to the time occupied by the wave crossing backwards and 

 forwards. 



Beardmore, the hydrauho engineer, while describing the effect of tidal 

 disturbances in rivers, remarks, — " When the reaches of the rivers are 

 straight the bore travels evenly up the river ; but at turnings it is thrown 

 off towards the further side, where it rises higher than in the straight 

 reaches. Thence it recoils and impinges upon the opposite shore, and so, 

 like a disturbed pendulum, it oscillates from side to side, and only regains 

 its steady course when the reaches lengthen." 



Were the shores of the lake flat and sloping, with the depth of water 

 graduaUy shoaling off, a wave of this description would be carried by its 

 impetus up the slope, consequently rapidly parting with its energy. The 

 shores of the lake are, on the contrary, almost perpendicular rocky cliffs, 

 with deep water close up to them, thus assisting the transmission of an 

 oscillating wave. 



The width of the lake ojiposite Queenstown is about three miles, but a 

 wave as before described would, in consequence of travelling a diagonal 

 course, considerably increase the distance. On the accompanying sketch of 

 the lake (Plate XIV.) I have indicated what I consider the probable 

 direction that this wave would take, which in crossing opposite Queenstown 

 measures about five miles, or ten miles during each pulsation ; and having 

 observed the intervals to be five minutes, it naturally follows that its 

 velocity would be 120 miles per hour. Assuming this to be the case, 

 according to Professor Airy's formula, it would necessitate a depth of 1,000 

 feet. 



Soundings have been taken,* and the greatest depth off Collins Bay is 

 given as 1,296 feet, the bottom rising gradually towards the head of the 

 lake, so that I assume the depth of that portion between the two bends to 



* Hector : Beport Geol. Surv. Ofcago, Prov. Council Papers, 1864, p. 86 ; and " Trans. 

 N.Z. Inst.," vol. n., p. 373. 



