634 PROCEEDINGS OF SECTION H. 
coming from the .mountains, some from the plains. 
Receiving floods at very various times, the lake remains 
unaffected until the rainy season, when from the end of 
May it slowly rises until it has attained its full height ; and 
not until the end of July does it begin slowly to fall. A 
case on a smaller scale may show the action of erratic 
floods reduced to regularity; thus the Brunner Lake, in 
New Zealand, is a sheet of water of about 18,000 acres, and 
receives two small rivers, and many creeks, taking their 
dvainage from neighbouring mountains. The outlet of the 
lake is by the Arnold, a most beautiful river, free from 
floods and all disturbances. The two rivers and the creeks 
which flow into the Lake Brunner are subject to terrific 
floods, but the effect is merely to raise the lake a foot or 
two; the ,outlet River Arnold is correspondingly raised a 
foot or two, and the steady flow continues till the floods are 
over. This is the same effect in another form of the floods 
of the various tributaries on a great parent river like the 
Nile. 
The effects of floods in rivers are subject also to the 
conditions of the rivers. If they descend from steep 
mountainous country into great plains, the plains are liable 
to suffer severely from floods, and all the more as the rivers 
are usually very crooked on alluvial plains—in fact, from the 
nature of things they cannot be otherwise; the softness of 
the soil forming the banks is the measure of the swiftness 
of the current that can flow between them with the least 
amount of change from erosion; therefore, the softer the 
alluvial soil of the plain the more crooked will the 
river be that flows through it. In the Hunter River of 
New South Wales I noticed a strange phenomenon in a part 
of the river where the twists and turns through the alluvial 
plains were unusually numerous. The general fall of the 
plains was about one in two thousand, but the fall of the 
river along its winding course was only one in nine thousand. 
When a flood commenced to reach this part of the river, the 
winding and twisting part slowly filled up, slightly increas- 
ing its sluggish current as the depth increased. As soon, 
however, as the’ flood rose somewhat above the banks, so 
that the plain became inundated, the river-channel ceased 
to act, or rather it flowed the wrong way; because in those 
loops and bends in which the flow was usually against the 
general fall of the plains, as soon as the flood overflowed 
the banks, the inclination of the surface of the water in 
such bends was directed towards the general fall of the 
valley, and the water being higher on the down-stream end 
