68 THE KANSAS CITY BRIDGE.

caisson, while the material under the edge was but slightly disturbed ; the sand
round these holes would then fall in, bringing with it considerable quantities of
sand from the outside ; but the slides seldom extended far enough along the edge
to cause any material settlement in the caisson. A water jet, attached to a long
piece of gas pipe, and handled with lines from above, was passed around the edge
of the caisson on the inside, which helped greatly to clear away any interior sand
bearing, to level off the material, feed the dredges, and let the caisson down ;
the dredges were usually run during the greater part of the day, excavating a
moderate quantity of silt and sand, but causing no perceptible descent ; they
were then stopped, and the pumps started, when an hour or two of jetting would
be accompanied by a few inches settlement. The material excavated was at
first a fine silt; but as the depth increased it changed to a coarse sand, in which
were found occasional masses of clay, and a few stones. In one instance the
caisson reached what appeared to be a thin continuous layer of clay, which the
dredges worked through without producing any general effect, and which had
to be cut in pieces with chisels from above.

On the 27th of April a second section was added to the caisson, which was
loaded with a wall of rubble masonry, between the timbers, like the first section.
On the 5th of May the machinery was stopped, the dredges rearranged by
transferring their support to the top of the second section, and started again on
the 14th. To secure additional weight, a box five feet by four was built around
the caisson, supported by brackets on the outside and filled with sand. On the
dth of July a third section was added, and the sand boxes were raised to prevent
their taking a bearing on the outside sand. About this time the summer flood
covered the sand bar, so that these works could only be reached in boats. The
level of the bar, between this pier and No. 7, was raised by a fresh deposit of
two or three feet of silt, and its general line was extended about twenty yards
towards the south, carrying it beyond the site of No. 5, but no material changes
occurred immediately around the caisson ; the current caused by the obstruc-
tions of the work, and the frequent sand-slides about it, prevented the accumula-
tion of any deposit, leaving the works in a little bay by themselves, and the
operations were not in the least disturbed by the high water.

On the 15th of August the base of the caisson reached an elevation of 80,