1918.] The N.Z. Journal of Science and Technology. 59- 
This flat extends for some distance up the valley of the latter stream.. 
North of the village of Puketurua three rocky knobs or buttes, formed o£ 
rhyolitic tuff, rise about 100 ft. above its surface. On the western side of 
the river, opposite the south-west corner of the Waipa Flat, the Waikato 
is joined by the Waiteti, a small stream that rises on the southern slopes 
of Maungatautari. The middle terrace extends along this stream as a 
flat-bottomed valley from 40 chains to 60 chains in width. Four miles, 
above its junction with the Waikato the Waiteti issues from the slopes of 
Maungatautari and enters this wide valley, which continues southward with 
a gentle easterly curve that must carry it once more to the present valley 
of the Waikato. 
Down-stream from Aniwhaniwha the middle terrace is prominently 
developed as far as the head of the Maungatautari Gorge. From this point 
it is continued as a flat-bottomed valley more than half a mile in width. 
This, the Hinuwera Valley, slopes gently in a north - easterly direction 
towards Matamata. Where it overlooks the Waikato its height above sea- 
level is 360 ft., while four miles northward of this point it is 330 ft.. 
A shallow channel, once occupied by the river that formed this ancient 
valley, and wide enough to contain the present Waikato, swings gently 
from one side to the other. 
Below the Maungatautari Gorge the Waikato enters its middle basin,, 
a wide alluvial plain, which is here about 300 ft. above sea-level. This 
plain, which as a wedge-shaped flat penetrates between the Maunga- 
kawa Hills and the spurs of Maungatautari, has undoubtedly been 
formed by the smothering of an old land-surface with loose pumice 
sands of fluviatile origin. Near the lower end of the gorge two low 
rounded hills entirely surrounded by alluvium rise above the plain,, 
and similar hills occur at Hamilton. It should be noted that even in 
the narrow portion ot the plain which penetrates the hills, and which 
partakes of the nature of a valley-floor, there is no trace of terraces 
fringing the hill-slopes. On the other hand, along the Hinuwera Valley,, 
which, although it drains to another river-system and is separated from 
the Waikato by the Maungakawa Hills, must still be regarded as an off¬ 
shoot from the same plain, there are remnants of higher river-terraces 
on the flanking hills. These correspond with the denuded highest set of 
terraces occurring along the Waikato Valley in the neighbourhood of 
Aniwhaniwha. 
The evidence shows that the present Waikato follows its old course only 
between the gorges ; northward it once flowed toward Matamata by way 
of the Hinuwera Valley, while southward its old channel lay between the 
Arapuni Gorge and Maungatautari. The valley in which the river then 
flowed had probably been excavated to as great a depth as that now 
existing. For some reason, either from a decrease in the carrying-power 
of the stream or from an increase in its load, the old valley was filled in.. 
The most plausible explanation, is that the land was depressed relatively 
to the sea rather more than 200 ft. This checked the current and caused 
the filling-up of the valley with pumice sand brought from the Taupo 
region. Toward the close of this period the river flowed in a shallow 
channel in a wide flood-plain now represented by the middle terrace.. 
About fifteen miles of this old flood-plain has been examined and found to 
have a regular grade of about 7 ft. per mile. While this flood-plain was 
being built the stream would tend readily to change its course ; in places 
it would flow in braided channels, and shallow lateral lakes, similar to 
those in the neighbourhood of Huntly, might form. As the spurs from 
