610 Transactions, — Geology, 



end, but in connection witli it I may here mention timt the first shaft sunk 

 by Messrs. Smith and Knight, tlie Englisli contractors, unfortunately 

 readied it soon below the surface of the ground, and continued all the way 

 through it to the roof of the tunnel. 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, which might be the continuation of No. 237, 11^ 

 chains from the Lyttelton end. This stream throws a great deal of light by 

 its COD figuration on the manner of the flow of liquid lava. After flowing 

 down the slopes, we see it shortly afterwards ascend again (No. 202) over a 

 bed of agglomerate, and, after having 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 begins about 41 chains from the Lyttelton end, and con- 

 tinues 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 jointed, 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 sphasrosiderite. 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 communication were stopped before 

 the whole of the gases still remaining in the southern parts of each had 

 been absorbed. 



Another stream of large dimensions is No. 14, beginning 20 chains from 

 the Heathcote end. It is over 100 feet thick, has a jointed structure, the 

 central portion beiug 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 their upper portion, the bottom of the streams, owing to 

 their thinness and to the distance from the centre of eruption, not having 



