603 Transactions, — Geology, 



64 lava- streams formed of a scoriaceous basaltic and doleritic lava, 

 some of them changing so gradually into agglomeratic beds 

 that the line between them cannot be clearly defined, 

 39 beds of agglomerates, a few of them changing into scoriaceous 

 lava, but most of them consisting of scorise, lapilli, and other 

 ejecta, imbedded in ashes, A few of them have a brecciated 

 appearance. 

 19 beds of laterite, clays, and slope deposits, partly or wholly burnt 



by overlying lava-streams, and 

 1 small layer of bolus — together 174. 

 These beds are intersected by 32 dykes, 18 consisting of trachyte lava 

 (of which five do not reach to the roof of the tunnel), and 14 of a basic 

 nature (five of them being intermediate in character, trachy-dolerites). One 

 of them comes from the top of the tunnel. 



Beginning at the southern or Lyttelton side of the tunnel, w^e observe 

 that a large bed of loam has been deposited upon the volcanic rocks, being 

 thickest on the lowest third of the caldera wall. This peculiar rock, which, 

 when in small pieces, is easily pulverized between the fingers, has a re- 

 markable consistency and solidity when in large masses, and is of sub- 

 aerial 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 scorite, lapilli, and ashes is, as might be ex- 

 pected, 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 at Lyttelton form a notable instance. They were without doubt 

 deposited on the lip of the crater. Near the Lyttelton end they are much 

 disturbed. Two stony lava-streams cross these agglomerate beds, and we 

 have to assume that after No. 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 234a, were formed, a new stony 

 lava-stream, No. 237, ascended, in which case Nos. 231, 234, and 238 to 

 241 were three distinct agglomerate beds, covered and preserved on their 



