ere. But shale is always a deceptive material. Subjected to
the influence of the atmosphere, it gives but a treacherous support. In
this case, falling away like quicklime, 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 and my
head, if that tunnel ever give way, so as to cause danger to any of the
public passing through it. 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,--though an engineer might well be beaten in his calculations, for
he cannot beforehand see into those little fractured parts of the earth
he may meet with." As Stephenson had promised, the invert was put in;
and the tunnel was made perfectly safe.

The construction of this subterranean road employed the labour of above a
thousand men for nearly four years. Besides excavating the arch out of a
solid rock, they used 23,000,000 of bricks, and 8000 tons of Roman cement
in the building of the tunnel. Thirteen stationary engines, and about
100 horses, were also employed in drawing the earth and stone out of the
shafts. Its entire length is 2869 yards, or nearly 1.75 mile--exceeding
the famous Kilsby Tunnel by 471 yards.

The Midland Railway was a favourite line of Mr. Stephenson's for several
reasons. It passed through a rich mining district, in which it opened up
many valuable coalfields, and it formed part of the great main line of
communication between London and Edinburgh. The Act was obtained in
1836, and the first ground was broken in February, 1837.

Although the Midland Railway was only one of the many great works of the
same kind executed at that time, it was almost enough of itself to be the
achievement of a life. Compare it, for example with Napoleon's military
road over the Simplon, and it will at once be seen how greatly it excels
that work, not only in the constructive skill displayed in it, but also
in its cost and magnitude, and the amount of labour employed in its
formation. The road of the Simplon is 45 miles in length; the North
Midland Railway is 72.5 mile