The life of George Stephenson, railway engineer - Lighthouse ...

CHAP, xxvii.] ACCIDENT TO LITTLEBOROUGH TUNNEL. 33I
the excavation passed at that point, was considered so hard and
firm, as to render it unnecessary to build the invert very strong
there. But shale is always a deceptive material. Subjected to
the influence of the atmosphere, it gives but a treacherous sup-
port. In this case, falling away like quickUme, it had left the
lip of the invert alone to support the pressure of the arch above,
and hence its springing inwards and upwards. Mr. Stephenson
directed the attention of the visitors to the completeness of the
arch overhead, where not the slightest fracture or yielding could
be detected. Speaking of the work, in the course of the same
day, he said, " I will stake my character, my head, if that tunnel
ever give way, so as to cause danger to any of the public passing
through it. The fracture that has taken place must, doubtless,
be a disappointment (o the directors, by delaying the opening of
the line ; but the fact is, that the invert is covered with material,
so that we could not find it out till that material was taken away,
so as to make the culvert through to carry the water from end
to end ; but I believe that if the invert were taken away alto-
gether, the tunnel would stand firm. It is a question now with
me, whether we ought to put the invert in again, or to strengthen
the foot of the side walls. However, it being a work of such
magnitude, it is perhaps safer to take a little more time to it,
and make it perfect. "With respect to the tunnel, taking it as a
whole, I don't think there is such another piece of work in the
world. It is the greatest work that has yet been done of this
kind, and there has been less repairing than is usual. Indeed,
no tunnel of such magnitude have I known with so little re-doing
of the work. It is a great work—thpugh one where an engineer
might be beaten in his calculation^, for he cannot beforehand see
into those little fractured parts of the earth he may meet with.
This is a dislocated part of a very high country, where the
debris has come off at a time and in a place where we could
have no chance of examining it, except by excavation. But
this is the only weak part we have met with. It runs diagonally
across the tunnel. It begins at one end of the fractured part and
runs to its other end. It is a part that has chipped off from its
neighbours, and not being so firmly fixed as the adjoining rocks
on each side, when we took off the bottom it eased a little, and
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