t pumping was necessary at many points to
enable the works to proceed. For a year and a half the contractor went
on fruitlessly contending with these difficulties, and at length he was
compelled to abandon the adventure. The engineer then took the works in
hand for the Company, and they were vigorously proceeded with.
Steam-engines were set to work to pump out the water; two locomotives
were put on, one at each end of the cutting, to drag away the excavated
rock and clay; and 800 men and boys were employed along the work, in
digging, wheeling, and blasting, besides a large number of horses. Some
idea of the extent of the blasting operations may be formed from the fact
that 25 barrels of gunpowder were used weekly; the total quantity
exploded in forming this one cutting being about 3,000 barrels.
Considerable difficulty was experienced in supporting the bed of rock cut
through, which overlaid the clay and shale along each side of the
cutting. It was found necessary to hold it up by strong retaining walls,
to prevent the clay bed from bulging out, and these walls were further
supported by a strong invert,--that is, an arch placed in an inverted
position under the road,--thus binding together the walls on both sides.
Behind the retaining walls, a drift or horizontal drain was provided to
enable the water to run off, and occasional openings were left in the
walls themselves for the same purpose. The work was at length brought to
a successful completion, but the extraordinary difficulties encountered
in forming the cutting had the effect of greatly increasing the cost of
this portion of the railway.

The Tunnels on the line are eight in number, their total length being
7336 yards. The first high ground encountered was Primrose Hill, where
the stiff London clay was passed through for a distance of about 1164
yards. The clay was close, compact, and dry, more difficult to work than
stone itself. It was entirely free from water; but the absorbing
properties of the clay were such that when exposed to the air it swelled
out rapidly. Hence an unusual thickness of brick lining was found
necessary; and the engineer afterwards informed the author that for some
time he entertained an apprehension lest the pressure should force in the
brickwork altogether. It was so great that it made the face of the
bricks to fly off in minute chips which covered his clothes whilst he was
inspecting the work. The materials used in the buildin