356 Geology of 



Beginning at the southern or Lyttleton side of the tunnel, we 

 observe that a large bed of loam has been deposited upon the volcanic 

 rocks, being thickest on the lower portion of the caldera wall. This 

 peculiar rock, which, when in small pieces, is easily pulverised 

 between the fingers, has a remarkable consistency and solidity 

 when in large masses, and is of suba?rial origin. It may be 

 designated as loess, an expression now extensively used in Europe 

 for similar deposits. It owes its origin to various processes, of 

 which rain, wind and vegetation are the principal factors. This 

 bed of loess, which in some localities, is more than 100 feet 

 thick, changes gradually before we reach the volcanic rock, to a 

 true slope deposit, consisting of fragments of rock more or less 

 rounded, the lines of junction being often impossible to trace, owing 

 to the decomposition of the volcanic rocks immediately below the 

 slope deposits. The greatest amount of agglomerate, consisting of 

 scoria^ lapilli, and ashes is, as might be expected, congregated on the 

 inner side of the caldera wall, not far from the focus of eruption. 

 These more or less incoherent beds, of which each was probably formed 

 during one eruption, have generally an inward as well as an outward 

 dip, of which the beds 232 to 241 close to the entrance of the tunnel in 

 Section Xo. 1, and extending 20 feet still more to the south, than shown 

 in that section, form a notable instance. They were without doubt 

 deposited on the lip of the crater. Xear the Lyttelton end they 

 are much disturbed. Two stony lava-streams cross these agglo- 

 merate beds, and we have to assume that after Xo. 231 was 

 formed, the lava-stream 233, ascending from the mouth of the 

 crater, had consolidated over it, being in its turn covered by a new 

 talus of ejecta sloping inwards to the crater's mouth. After these 

 latter beds, 234 and 231a were formed, a new stony lava stream, Xo. 

 237. ascended, in which case Xos. 231, 231, and 238 to 211 were three 

 distinct agglomerate beds, covered and preserved on their inner slope 

 "bv stonv 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 around the crater's mouth — a 

 phenomenon frequently observed during violent volcanic eruptions, 

 when a hu^e ciuder cone is formed in a short time. A similar occur- 

 rence seems to have taken place more towards the centre of the 

 tunnel (Section Xo 1), about 60 chains from the Lyttelton side, where 

 a large stony lava stream, No. 167, is seen to ascend through the 

 ao-crlomerate bed or beds, Xos. 166 to 16S. Thelava stream, 163, in close 



