proves that, when they fail to adopt his advice about it, they are generally sorry therefor by the time the work is finished.

Coffer-dams are liable to give trouble in several ways: first by leakage, second by flooding, and third by collapsing. If a Contractor gets through a large piece of coffer-dam foundation work without accident or trouble of some kind he is in great luck.

For bare bed-rock, movable coffer-dams may be employed; but they are troublesome to construct, and are sometimes very difficult to remove because of a deposit of sand taking place while the piers are being built.

The pneumatic process for sinking piers is in most cases the best one to employ, the only objection to it being the excessive cost of installing the plant, even if one has a complete outfit at his disposal. Its great advantages are that it enables the contractor to overcome, in the cheapest and most expeditions manner possible, all obstacles that may be encountered in sinking; and that it ensures the obtaining of a satisfactory foundation for the piers. It can be used for depths as great as one hundred feet or even more, although there is considerable danger to the workmen when the depth exceeds eighty or ninety feet.

Most of the bridge-piers which the author has put in have been sunk by the pneumatic process; and be has no hesitation in recommending it as the most satisfactory, all-around method in probably nine cases out of ten which occur in a consulting engineer's practice.

The open-dredging process is suitable for very deep foundations, or for putting down caissons that are to rest on the sand, or for bed-rock foundations where there is no liability of great scour. For large piers this process is much cheaper than the pneumatic on account of both the smaller cost of plant and the more rapid progress in sinking. In case, however, that obstacles be encountered, such as trees or large boulders, the expense for sinking is liable to run high, as these obstacles may have to  be  removed  by  a  diver  or  divers,  which  always  involves  great  expense.   The  author  has  put  down  three  large  piers  by   the   open—dredging   process,    two   to   a    depth    of    ninety