Haasr.—On the Geological Structure of Banks Peninsula. 509 
inner slope by stony lava-streams, consolidated during their ascent. Or, 
to offer another explanation, we might regard these two stony lava-streams, 
233 and 237, as having broken through the huge accumulations of ejecta 
which were heaped up all round the craters mouth—a phenomenon 
frequently observed during violent volcanic eruptions, when a huge cinder 
cone is formed in a short time. A similar occurrence seems to have taken 
place more towards the centre of the tunnel, about 60 chains from the 
Lyttelton side, where a large stony lava-stream, No. 167, is seen to ascend 
through the agglomerate bed or beds, Nos. 166 to 168. The lava-stream, 
163, in close proximity, might be considered to be the continuation of the 
former, which here flows down the steep side of the cinder cone. Gradually, 
as we retreat from the focus of eruption, the agglomerate beds decrease in 
number and size, but they still are occasionally present even close to the 
mouth of the tunnel near to the Heathcote entrance. Some of them con- 
sist in their lower portion of fine ashes, or lava d’aqua, and above of scorie 
and lapilli, so as to suggest that first fine ashes had been thrown out or 
had been brought down the side in the form of a mud stream, on the top 
of which large ejecta were afterwards deposited. Another agglomerate bed 
having an anticlinal or saddle arrangement is 224, 17 to 20 chains from the 
Lyttelton end; it was evidently deposited on the rim of the crater, of 
which the uneven surface is well visible in its lower portion. After its 
formation, two more agglomerate beds were deposited over it, 216 and 227, 
and 211 and 228 in the section, each being separated from the other by a 
bed of laterite. Moreover, it is clear that, whatever may have been its origin, 
the lowest portion of this and several other agglomerate beds must have 
been deposited when in a state of high temperature, as the argillaceous bed 
below it has been burnt red, so as to take all the characteristics of a laterite. 
All round Banks Peninsula agglomerate and ash beds are visible in the 
cliffs, but they are like the lava-streams of small vertical extent only, and 
we have to approach more towards the centre of eruption when we wish 
to see them in their greatest dimensions. 
The largest and most numerous stony lava-streams are met with towards 
the centre of the tunnel, where the basalt of which they are composed 
possesses the greatest hardness and crystalline texture. More towards the 
boundaries of the volcanic system, the lava-streams are much thinner and 
at the same time more porphyritie, amygdaloidal or scoriaceous, and it is 
very instructive to follow some of the lava-streams which form clear sections 
in the deep valleys radiating round the peninsula, from the summit of the 
caldera wall to their termination at its foot, and to note the gradual change 
in their size, and in the texture of the rocks of which they are composed. I 
have already alluded to the lava-stream 237, nine chains from the Lyttelton - 
