Haast, — On the Geological Structure of Banh Peninsula. 507 



sliowing some remarkable irregularity, is the one in wliich tlie so-called 

 Ellis Quarry is situated. Tins dyke, wlncli strikes nearly east and west, 

 goes out about 400 feet below the summit, where a saddle intersects the 

 spur. Shortly above its lower termination it sends off a smaller branch in 

 a sonth-west direction, also ceasing after a short course. Whilst the main 

 dyke does not appear any more above the surface, the smaller south-western 

 branch crops up again on the other side of the depression, now gradually 

 changing its direction, so that, in its lower course, about 300 feet above the 

 plains, it crosses the spur in a south-east and north-west direction. The 

 whole system of dykes in the Lyttelton caldera wall is thus very different 

 from the dykes of Mount Somma, of which, in his paper, Mr, E, Mallet 

 gives us such a lucid and suggestive account, and of which many are 

 fractured, displaced, and crushed, and have at the same time a wedge- 

 shaped form. We can, therefore, assume that the fissures and dykes in the 

 Lyttelton caldera were only formed after the latter had been so thoroughly 

 consolidated that, after the formation of the fissures and their filling up by 

 the principal dykes, no more changes of any importance took place in them ; 

 and that, moreover, the forces by which the walls of the volcano were 

 starred from top to bottom, must have been far deeper-seated and more 

 effective than the agencies by which Mount Somma was rent. 



In conclusion, I wish to lay before you a few notes on the geological 

 features of the Lyttelton and Christchurch railway tunnel, of which I made 

 a careful survey during a number of years, as the work of the miner 

 advanced. I watched this interesting and instructive work with great 

 attention, this being the first time that a caldera wall of a large extinct 

 volcano was to be pierced through, I prepared at the time a section on a 

 scale of liu. to 20ft., which I have great pleasure in laying before you, . 



The direction of the tunnel is N, 14° W, The first trial shaft was 

 commenced in January, 1860, and the permanent works under contract 

 with Messrs, Holmes and Co., began in July, 1861, The tunnel was laid 

 out, and its execution solely superintended by Mr. Edward Dobson, C.E., 

 Provincial Engineer. It was brought to a successful termination on May 

 25, 1866, when both adits met near the centre. The opening for railway 

 traffic took place on December 9, 1867. The total length of the tunnel is 

 8,598 feet, and if we deduct from this 365 feet on the northern or outer 

 side, and 105 feet on the southern or inner side, formed by slope deposits 

 and loess, there remains 8,128 feet of rock of volcanic origin, of which the 

 caldera wall has been built up. Classifying the rocks according to their 

 lithological character, we find that the crater above the present waterline 

 consists of — 



61 lava-streams, having the character of a stony compact or por- 

 phyritic basalt. 



