Sob Geology of 



This was one of the principal causes that the firm, being unacquainted 

 with the formation of the crater wall, abandoned the contract so 

 soon. The first stony lava in the tunnel, flowing down the slopes of 

 the crater wall, is a small stream, No. 214, about 22 chains from the 

 Lyttelton end. Several others of similar dimensions follow, till we 

 reach stream 206 (Section No. 2), which might be the coutinuati n of 

 No. 237 (in Section No 1), 11^ chains from the Lyttelton end. 

 This stream throws a great deal of light, by its configuration, on the 

 manner of the flow of liquid lava. After flowing down the slopes, we 

 see it shortly after tvard ascend again (No. 202) over a bed of agglo- 

 merate, and, after haying reached the apex of the latter, descend 

 again (No. 200), diminishing rapidly in size, the rock now becoming 

 highly porphyritic and lighter in colour. The largest stony lava- 

 stream of the whole series, of which Section No. 3 gives a portion, 

 begins about 41 chains from the Lyttelton end, and continues without" 

 interruption to 52i chains. Consequently, taking its angle of dip into 

 account, it is more than 500 feet thick. More or less porphyritic on 

 both sides, the whole central portion consists of a very hard basaltic 

 rock, ringing to the hammer, irregularly joint dd, with here and there 

 a tendency towards spheroidal structure. This huge stream gains an 

 additional interest from the existence of three caves in its centre, 

 which, however, have partly been filled up with thin plates of basalt of 

 the same texture as the lava-stream, and which lie more or less 

 horizontal. They are coated over and often cemented together by 

 sphaerosiderite. Sometimes they lie in such regular order, and so 

 loosely upon each other as if they had been artificially placed in that 

 position. The open space, or cave proper, is always on the southern 

 side of each cavity. The only explanation I can offer as to their 

 formation is that gases have been enclosed in this portion of the lava- 

 stream, which, in course of time, were absorbed, and that liquid 

 matter from the upper portion of the stream found access to the 

 cavities, gradually filling them up, but that the channels of communi- 

 cation were stopped before the whole of the gases still remaining in 

 the southern parts of each had been absorbed. 



Another stream of lar^e dimensions is No. 14, beofinnino- 20 chains 

 from the Heathcote end (Section No. 6). It is over 100 feet thick, 

 lias a jointed structure, the central portion being spheroidal, with 

 concentric layers. All the stony streams in the tunnel above the 

 latter are very thin, but it is possible that the scoriaceous basaltic 

 lava (the violet beds of the section) which overlie them, are only 



