82 Transactions.— Miscellaneous. 
lateral streams contain considerable quantities of boulders and gravels 
which floods of ordinary magnitude are incapable of moving, the larger 
rocks and boulders serving as dams or buttresses for supporting smaller | 
matter above them. But, whatever the relative size and force of these 
lateral streams may have been, there was one character which they all had 
in common before the occurrence of the great floods of 1868, namely, that 
they had evidently never changed their courses, at all events for some 
distance upwards from their debouchures onto the main terrace, since this 
had been left permanently above water by the cutting down of the present 
main river-channel. This is a point of great importance, and to be care- 
fully borne in mind in connection with the observations referred to in the 
sequel. The hills and mountains on each side of the gorge are steep and 
hummocky, generally bare of forest, but covered with tussock grass and 
fern, and with the other vegetation characteristic of such localities in the 
South Island. 
The valley of the main river rises from about 800 fect at the mouth 
of the gorge to about 1200 at its upper end in the Hanmer Plain, Mount 
Tekoa, on its western side, attaining an elevation of upwards of 5000 feet on 
a base of less than ten miles from the bank of the river. I am bound to be 
thus particular in describing the physical features of this gorge, and, indeed, 
of all the country in which I noticed extraordinary marks of the flood in 
question, because the changes effected by it in those physical features afford 
the chief proofs in support of my proposition. To these changes I will refer 
_after completing my general sketch of the country affected, so far as this is 
necessary for the purposes of this paper. The gorge I have been describing 
terminates at the Hanmer Plain, which, like that of the Hurunui, lie 
nearly east and west, and is also surrounded by mountains. The main 
river flows into the plain from a gorge at its western end, and after flowing 
along its southern side to about the middle of the plain, turns abruptly 
into the one which I have lately described. At the point where this occurs 
it is met by two small rivers, one called the Percival, flowing directly across 
the plain from the northward, and the other called the Hanmer, flowing 
from the westward in a course directly opposite to that of the main river: 
These rivers are very insignificant in size compared to the Waiau-ua, but 
in times of flood each of them brings down to the latter a large quantity of silt 
and gravel, partly derived from the shingle of the plain and partly carried 
into it by the innumerable rivulets which drain the surrounding mountain 
slopes. When, however, the whole of the rivers are in flood, the waters of 
the Percival and Hanmer are banked up at the confluence, and form a large 
expanse of practically still water, the effect being that, as in the case of the 
Pahau and the Hurunui hereafter referred to, a considerable quantity of silt 
