MEETINGS OF SOCIETIES. 581 
were continuous till 1874, the principal reduction of the special 
shoal occurring between 1872 and 1874. During that period the 
sand was being carried from the channel into the Peninsula, up 
the hills and over the cliffs into the ocean. 
Comparing the cross sections in the harbour at the two dif- 
ferent times, shows that while the disturbances are considerable, 
there is almost always a scour to account for a deposit, and that 
the whole lower harbour exhibits the usual characteristics of 
streams in having scour on the concave bank and deposit in the 
convex. These facts show that caution is necessary in stating the 
changes in a harbour, and that unnecessary fears should not be 
entertained with regard to such, because a bank may be making 
up in any one spot ; tor if so there is sure to be a deepening at 
some other. 
At the entrance to the Otago Harbour the waves come 9n to 
the beach at right angles and not obliquely, as at Timaru, and 
many other parts ot the east coast of New Zealand. In 1868 an 
earthquake wave scoured down to a depth of 22 teet at low water 
a huge portion of the bar which in its normal condition had only 
from 13 to 18 feet water on it, but it was restored to almost its old 
condition within two years. The experience in dredging also 
shows a heaping-up tendency by the wave action when dredging 
is suspended, and more especially in heavystorms. The great 
current setting northwards along the New Zealand coast does not 
come nearer the northern heads than about three miles, while it 
seems to strike about the ocean beach and then to be deflected 
seawards. This is an important point in connection with the pro- 
posal to carry the sewage of Dunedin to the neighbourhood ot the 
Lawyer’s Head. 
The currents that affect the banks at the Heads are principally 
those of the tides. The ebb sets out of the harbour in a direction 
about parallel to a line drawn from Harrington Point to Taiaroa 
Head, and about the northern extremity of the bar it meets the 
general ebb current coming south along the coast. At the nar- 
rows, Harrington Point, the mean velocity of the ebb is 23 knots 
per hour; off Taiaroa Head, and also when it clears the bar, 2 
knots per hour. Inthe line of leading lights it is only 13 knots, 
and in other parts from } knot to1 knot. There are less varieties 
in the rates of the flood tide, and indeed less of a defined stream. 
Its mean velocity at Harrington Point is 13 knots. ; 
When the steamer ‘“ Oreti’’ was wrecked at Pleasant River, 
one night about g o’clock, some of her cargo was floating at Otago 
Heads next morning, and came in upon the flood tide. When the 
‘* Bruce ” steamer was wrecked within a mile of the lighthouse, 
some floatage from her was inside the heads next morning. On 
both occasions there was very little wind, so that in the one case 
the articles were carried along by the ebb, and in the other by the 
flood tides. On the other hand, when a small vessel was wrecked 
on the bar, nothing from her was ever known to come ashore. 
A comparison of the depths on the bar in 1849 and 1879 
shows :-— 
: 1849. 1879. 
Least depth in line of leading lights -  16ft. 15it. 
We know, however, from soundings taken just before the dredge 
began to work, that the minimum depth at this part in the begin- 
