Haast. — On the Geological Structure of Banks Peninsula. 609 



inner slope by stony lava-streams, consolidated during tlieir 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 crater's 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 doAvn 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 scori® 

 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 22a, 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 Hke 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 porphyritic, 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 



