If the bottom is ten feet wide and thirty-five feet long, it will weigh

35 × 10 × 2 × 30 = 21,000 lbs.

one course of masonry weighs

30 × 6 × 2 × 100 = 57,600 lbs.

one course of side timbers, 12 × 12, which are laid upon the sides of the raft,

(2 × 35 + 2 × 8) × 30 = 2,580 lbs.

Now load the bottom with one course of masonry and three courses of side timbers, and we have

Stone57,600lbs.
Bottom of caisson21,000lbs.
Three side courses7,740lbs.
In all:86,340lbs.

which divided by 62, gives 1,392; which divided by the area of the caisson bottom, gives

1392
350 = 3.98