HiLGENDORF. — X(//iin// Fcafiires of Arthur's Pass Tunnel. 123 



for the boring of the holes into the rock for the temperature observations — 

 arranoenients that were continued when the work was taken over by the 

 Public Works Department. It was desirable that the temperature bores 

 should be as close to the working face as possible, so as to prevent the 

 cooling of the rock by the air of the tunnel, and so it was arranged that 

 the bores should be put in 4 ft. behind the working face of the bottom 

 heading, that they should be 5 ft. deep and 1 in. in diameter, sloping 

 slightly u])wards to prevent the accumulation of water in them, and lightly 

 I)lugged with tow to prevent the circulation of air. For ease of rediscovery 

 they were for most of the distance put in every 10 chains, at a height of 

 4 ft. from the floor, and on the east side of the tunnel. Different members 

 of the Committee visited the tunnel at various intervals, either to make 

 the observations or to note their progress in the hands of those to whom 

 they were deputed. The tunnel is not yet completed, but, as the bottom 

 headings have met, it is considered that no new phenomena are likely to 

 be disclosed. The results of the observations are almost entirely negative. 



Rock Structure. 



The course of the tunnel is entirely through rocks of the Maitai system. 

 Its direction makes a small angle with the axis of an anticline, and 

 therefore little can be learned of the order of occurrence of the various 

 beds. There are the usual variations from coarse-grained light-coloured 

 to fine-grained dark-coloured beds, and through these run irregular veins 

 of Cjuartz and occasionally of calcite. Some of the rocks, particularly 

 those of the fine-grained type, are distinctly carbonaceous, and are found 

 to contain in places nests and lenticular masses of impure graphite. All 

 the rocks are somewhat calcareous, and contain in one or two places 

 nodular concretions about the size of a hen's egg. A record of the dip 

 and strike of the veins running through the country rock was kept for some 

 miles from the Otira end, and this record is in the hands of the Public 

 Works Department. 



Owing to the rocks ex]>osed being in the axis of an anticline they are 

 frequently faulted, and are broken and shattered to a high degree. This 

 has had an imj)ortant effect on the permeability of the mass to water, as 

 will be noted immediately. 



A complete series of specimens of the rocks obtained throiigh the tunnel 

 has been prepared for preservation in the Canterbury Museum. 



Inflow of Water. 



The shattered nature of the rock allowed the ingress of much water, 

 and every time a blast opened up a wet seam streams of water would pour 

 down on the workmen, greatly retarding the progress of the tunnel. When 

 the bore was in 5 chains from the Otira end the influx of water was 0-1 cubic 

 f'»ot per second. The ]:)laces where the water came in worst were from 10 to 

 40 chains apart, and these usually occurred where the rock was crushed 

 and broken. In certain places the rock, shattered to pieces the size of a 

 walnut, flowed in with the water, opening up great seams that required 

 inuch timbering. The occurrence of the wet seams was most capricious. 

 For instance, on one occasion the bottom heading opened up quite dry, 

 but when the tunnel was enlarged to its full size a bad inflow of water was 

 struck. There was no relation between the amount of rock overhead and 



