Hieetnson.—On Floods in Lake Districts. 188 
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 pulsations 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 hydraulic 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 
gradually 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 opposite 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 1,996 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: Report Geol. Surv. Otago, Prov. Council Papers, 1864, p. 86; and “Trans, 
N.Z. Inst.," vol, IL, p. 373. 
