160 



TUNNELLING THUOUGH VARIOUS STK.VTA. 



used, as it was found choapor to blow it ont in larf!;o masses. 

 A considorablo length of this tunnel was not lined, especi- 

 ally where a rock top was obtained, and very little had side- 

 walls. Whore lining was required, it was in nearly every 

 case only in the form of a flat fly arch springing off the rock 

 or hard sand-sides of the tunnel. In many instances as 

 much as 22 yards of heading per week was driven, by hand 

 labour, through this compact sand. The author considers 

 that there are not many instances of tunnels being com- 

 pleted in so short a time, as it must bo remembered that, 

 as was before stated, the tunnel was over 1,000 yards in 

 length, and constructed entirely without shafts, the only 

 shafts being at the ends of the tunnel, and sunk chiefly for 

 lowering materials into the tunnel without obstructing the 

 cuttings, no spoil being, in either case, wound up the shafts, 

 nor were they used in any way for driving the tunnel. Of 

 course it must also bo borne in mind that the ground through 

 which the tunnel was driven was unusually favourable, and 

 in very few instances would such favourable conditions be 

 likely to arise. If the author remembers correctly, the 

 tunnel was straight from the Bath end, and on a curve of 

 40 chains radius at the Midford end, the Bath end being 

 nearly level, and the Midford end for a considerable distance 

 on a gradient of 1 in 50. 



It was, no doubt, an error to suppose that this tunnel 

 would turn out very wet on account of the large streams 

 of water issuing from the hill not far from its summit; and 

 it was overlooked that between the proposed tunnel and tho 

 water lay the Fullers Earth, which is in itself impervious 

 to water, and a great water-basin, from which, no doubt,, 

 the streams of water issued. Most water was met with in 

 the bottom of the tunnel, and hardly any from above; and 

 tho only water i'ound was in the rocky portions, the hard 



