Canterbury and Westland. 355 



The Chbistchukch and Lyttelton Railway Tunnel. 



In the Historical Notes on pages 62 and 156, 1 hare alluded to the 

 geological survey undertaken by me during the progress of the 

 interesting and instructive work of passing through the caldera wall 

 of a large extinct volcano. I prepared at the time a section at the 

 scale of 20 feet to 1 inch, and have reduced, for this report, some of 

 Its most interesting portions to half that size. — Vide coloured 

 Plate III. 



The direction of the tunnel is K 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 8598 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 8128 feet of rock of volcanic origin, of which the caldera wall 

 has been built up. Classifying the rocks according to their litho- 

 logical character, we find that the crater above the present water-line 

 consists of — 



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

 porphyritic basalt. 



54 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 scoria- 

 ceous lava, but most of them consisting of scoria?, 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. 



