58 The N.Z. Journal of Science and Technology. [Jan. 
An excellent section of the tuffs is exposed along the Arapuni Gorge. 
In the neighbourhood of the proposed dam-site the lowest rock observed 
contains scattered pebbles of andesite, obsidian, and greywacke. This is 
at least 50 ft. thick, and is overlain (junction obscured by talus) by layers 
of a soft dark-coloured tuff, which grades upward into a light-coloured well- 
consolidated rock at least 90 ft. in thickness. Two or three feet of fine¬ 
grained material containing carbonaceous matter next succeeds, and this 
passes into a rather soft pumiceous sandstone 30 ft. thick. The fine-grained 
dark material is considered to mark an old land-surface, which is here 
150 ft. above the stream, but which, owing to a southerly slope, reaches 
the river about half a mile up-stream. There a pumice conglomerate of 
fine texture occurs beneath the soft pumiceous sandstone, which has greatly 
thickened and forms vertical cliffs 400 ft. to 500 ft. high. This sandstone, 
which weathers to a dull reddish-brown colour, is capped by tuff which forms 
hills on both sides of the river. 
The old land-surface, mentioned above as intervening between the two 
sets of beds, must have been highly irregular. The wide uneven shelf 
which is prominent along the cliffs on both sides of the river up-stream 
from the dam-site is evidently composed of the lower tuffs, which are more 
resistant than the massive pumiceous sandstone that is here the lowest 
portion of the younger tuff beds. A few chains below the dam-site the 
gorge cuts across an old steep-sided valley the bottom of which reaches 
within 30 ft. of the river. So far as can be judged from the cliff-tops, this 
is filled with sandstone and conglomerate belonging to the younger series 
of tuffs. Probably the stratified sandstone at the Aniwhaniwha Rapids was 
also laid down at the same time. 
With the exception of the gravels and sands of the river-bed and low 
terraces the only other deposits in the district are pumice sands that fill 
an old river-valley. These are well seen near the upper end of the Maunga- 
tautari Gorge, where the Pairere Stream exposes along its valley-walls 
incoherent current-bedded sands, with occasional bands of gravel, to a 
depth of 150 ft. These sands have been laid bare at many other points 
in road-cuttings or along stream-channels, and everywhere are seen to have 
been formed by river-action. 
The valley of the Waikato between the Arapuni and Maungatautari 
Gorges is fringed by well-marked terraces. At some points seven or 
eight may be counted, and three of these extend for miles along the 
valley. The lowest important terrace has a general height of 80 ft. above 
the level of the stream below the rapids at Aniwhaniwha and above the 
rapids a height of 50 ft. There are at places two or three terraces at a 
lower level, but there is practically no flood-plain, the river being en¬ 
trenched to the depth stated above. The next important terrace is about 
160 ft. higher than the first, while the third is about 240 ft. This last 
terrace has been somewhat mutilated by denudation, and its surface, in 
addition, slopes more decidedly towards the river than do the surfaces of the 
other terraces. 
The lowest terrace stretches almost continuously on both sides of 
the river from one gorge to the other, while the highest has its chief 
development on the western side of the valley. The middle terrace, 
however, is much the most extensive. From Aniwhaniwha, where it is 
about 390 ft. above sea-level, it extends up-stream on both sides of the 
valley to the Arapuni Gorge. Below this point, to the eastward, it forms 
a high-level flat, 400 ft. to 420 ft. above the sea, one mile wide by two miles 
long, and lying between the Waikato and the lower course of the Waipa. 
