510 Transactions,—Geology. 
end, but in connection with it I may here mention that the first shaft sunk 
by Messrs. Smith and Knight, the English contractors, unfortunately 
reached 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 smail 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, 114 
chains from the Lyttelton end. This stream throws a great deal of light by 
its configuration on the manner of the flow of liquidlava. 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 52} chains. Consequently, taking its angle of 
dip into account, itis more than 500 feet thick. More or less porphyritie 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 spherosiderite. 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 commnnication were stopped before 
the whole of the gases still dues 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 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 basaliie 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 
