1882.] on the Mahing and WorMng of a Channel Tunnel. 123 



these holes. These are, popularly speaking, the two great divisions 

 of tunnel-making. 



There is, however, one well-known exceptional case, where a 

 tunnel was driven through an all but fluid material in the bed of the 

 river Thames. I mean Brunei's celebrated tunnel, now used as a 

 portion of the East London Railway. 



In ordinary railway tunnelling, such as we meet with in England, 

 it is commonly possible to sink shafts at frequent intervals, and 

 in this way to multiply the number of faces, or ends, at which men 

 can work ; but in the case of the great tunnels made of late years 

 under high mountains, such as the Mont Cenis tunnel, 7J miles long, 

 and the St. Gothard tunnel, 9J miles long, it is not possible, having 

 regard to the expense of the deep shafts, and the comparatively in- 

 accessible positions of their mouths, to accelerate the rate of progress 

 or to add to the ventilation by their use, and in such cases it 

 becomes necessary to do the whole of the work from the two ends. 



Hitherto I have spoken of railway tunnels. I may, however, be 

 permitted to remind you that the earlier tunnels made in England 

 were those employed for canal purposes ; these, however, must not 

 be further referred to, nor will I delay by calling your attention to 

 the great canal tunnel made in France in the year 1681, or to the 

 still earlier tunnel, the Grotto of Posilipo at Naples. 



Besides tunnels proper, there are subterranean workings, to 

 which the term tunnel is not applied, but which are undoubtedly as 

 strictly tunnels as are those through which trains pass or along which 

 barges are hauled. You are of course aware that I am alluding to our 

 great underground works for mining purposes. Here, at depths below 

 the surface varying from a few hundred yards to half a mile, and in 

 some few instances extending below the bed of the sea, we have 

 tunnels which even in a single colliery have an aggregate length of 

 many miles, excavated by means of only two shafts, and carried 

 through rock of the most varied character, and too frequently sub- 

 jected to the dangers arising from the firing of the gases, and from, as 

 we were so well shown a few weeks ago by Mr. Abel, the dangers 

 arising from the explosion of the dust with which these galleries are 

 in many places covered. 



As regards stratification, obviously, if it were a matter of choice, 

 neither the unstable earth, nor the clay which, although easily cut, 

 cannot be left for a moment without support by timbering, pending the 

 getting in of the permanent lining, would be selected, neither would 

 be chosen the rock which, although capable of standing alone, 

 demands for its excavation the labour and cost incident to 

 drilling and blasting operations, and demands also the great expendi- 

 ture of time needed for working under these circumstances. 



The perfect material, so far as regards its excavation, would be 

 one, which, while it was capable of being easily cut, was also capable 

 of self-support for a long time, if not in perpetuity ; and further, if in 

 addition to these two excellent qualities as regards excavation and 



