424 Transactions. 



the inflow of water, one of the worst flows being met with where the over- 

 burden was 900 ft. of rock. The course of the tunnel followed very nearh- 

 the courses of the Otira and Bealey Rivers, and several times passed under 

 these or their larger tributaries, but there was no relation between the 

 influx of water and the position of the tunnel in respect to these rivers. 

 As a general rule the entering stream dried up considerably in a few weeks 

 or months, but this was not always the case. The remaining flows, with 

 the smaller drips that are practically continuous throughout the length of 

 the tunnel, now produce a considerable stream, discharging 7 cubic feet 

 per second. As the concrete lining is placed in position the water is 

 confined behind the lining, which is pierced with weep-holes at sufficient 

 intervals. 



The concrete lining consists of a solid mass up the walls, but the arch 

 is formed of concrete blocks. Between these very small drips occur, and 

 the dripping water, having dissolved in it some of the materials of the 

 concrete, has on evaporation formed stalactites, which are very noticeable 

 objects as they hang from the roof. Their composition is essentially 

 CaCOg, with traces of Fe, Al, organic matter, and NHg, the last probably 

 from the organic matter. There is no Mg, PO^, or SO^. The stalactites 

 are about 1 ft. long, and about \ in. in diameter. They look solid as they 

 hang, but when broken from the roof are so fragile that they can hardly 

 be held in the hand without breaking, for they have a large hollow down 

 the centre, the solid matter forming the thinnest possible shell. Their 

 rate of growth has been about 2 in. per annum, which is probably a 

 hundred times as fast as stalactites grow in a limestone cave. The 

 difterence is due to the fact that in the case of the tunnel it is the 

 soluble calcium hydrate that the water has had to work on, instead of 

 the relatively insoluble calcium carbonate. It is probable that the rate 

 of growth may be temporarily increased by the through draught caused 

 by the opening of the bore from end to end, although the draught is 

 neither so considerable nor so constant as might be expected considering 

 that the tunnel is a mathematically straight line and is 860 ft. higher at 

 one end than at the other. The draught is usually upward, but sometimes 

 is qiiite absent and sometimes flows downward toward Otira. 



Rock Temperatures. 



When the tunnel was started it was designed to take at each of many 

 places three simultaneous observations as follows : — (1) The rock temperature 

 in the tunnel ; (2) the rock temperature at the nearest surface above the 

 temperature-hole in the tunnel ; (3) the radio-activity of the rock exposed in 

 the tunnel. By this means it was hoped to contribute to our knowledge of 

 whether, and to what extent, the internal heat of the earth is due to radium 

 emanations as distinct from its residual heat. The conditions were, how- 

 ever, most unfavourable. In the first place, though the tunnel pierces a 

 great mountain-chain, it passes under a low saddle, so that the overburden 

 of rock is at its maximum only 1,100 ft. If the tunnel had been two miles 

 east or west of its actual position the overburden would have been increased 

 to 4,000 ft. or 5,000 ft. In the second place, the great influx of water made 

 it quite clear that the observations would give the temperature not of 

 the rock, but only of the percolating water. Of the temperature-holes 

 bored half were distinctly wet, while the others were so near to wet places 

 that the rock and the thermometer were undoubtedlv affected bv the water. 



