52, THE KANSAS CITY BRIDGE.

completed within it, and the intermediate space, about five feet wide, was filled
with stone and sand. An ice-breaker, formed of an inclined sycamore log and
a fender of planked piles, was built above the pier site. In February a large
dredge, with a steam-engine to drive it, was mounted upon the caisson ; it was
set in motion on the 13th of that month, and lowered the caisson a few feet.
The rising water of the 8th of March produced a moderate scour, which aided
the sinking; on the 17th the scour increased very rapidly on the south side,
and the caisson began to tilt over ; the next morning the water was found to
be twenty-two feet deep there, while no corresponding wash had occurred on the
north side. Under the combination of this undermining of the southern cutting
edge, and the pressure of the sand against the north side, the caisson settled —
over till only the north-east corner remained above water. By hard work
through the morning and dinner hour the machinery was removed and placed
on boats. By 2... the whole caisson had disappeared; the weight of the
sand and stone with which the walls were loaded, together with the external
sand pressure, proved too great for so loose a structure ; it broke in settling,
and became a total wreck ; a few of the timbers cleared themselves, and floated
down stream, but the greater part of the wreck, being of green oak and covered
with sand and stone, remained at the bottom of the river.

The loss of this caisson put an end to the work which had thus far been
done on this foundation, making it necessary to start entirely anew. Moreover,
_the circumstances attending the wreck showed the exposure-of this site to be so
great that it was thought unwise to adhere to the plan of a pile foundation.
The situation of this pier, between the edge of the sand bar and the low-water
' channel, exposes it to more frequent washes and deposits than have been
‘observed elsewhere, while it is also liable to be subjected to the thrust of a
heavy bank of sand on the north side, with no counterbalancing pressure on the
south side, a danger from which the other piers are free. For these reasons it
was determined to treat this as a channel foundation in preparing the new plan,
and to extend the full-sized pier down to the rock. To avoid the difficulties of
passing through the old wreck, which would have made it necessary to resort _
to the use of compressed air, and which it was feared would have delayed the
completion of the bridge through another season, the location of the pier was