1815. In repairing this damage the three piers just west of the draw were surrounded with rubble stone work. To form a foundation "large quantities of stone were dumped in around the piles until they were heaped up to the water line. It is said they worked some time in getting in these stones, and that after everything was fixed to their satisfaction the masons went out one morning to build the piers, and found that their foundation had disappeared. It had sunk down through the soft mud forming the river bed. More stones were thrown in and the piers built up." "During the spring and summer of 1867 a portion of the stone forming one of the piers fell down." When the present bridge was built the three piers unimproved in 1815 were treated with stone, as the others had been. A result of this work since 1793, is that today, while the sectional area just above Washington bridge is 13,620 square feet at high water, and 11,020 square feet at low water, the corresponding water areas on the bridge axis or along the ridge of its foundation, are 3,810 square feet, and 2,370 square feet; 2,370 is 214 per cent. of 11,020. Originally the bottom on the axis was of very soft mud, which a stream running at a velocity of one-half mile per hour would, it is believed, serve to work up and move, so that it is to be presumed that before 1793 the stream had made for itself a channel at this point perhaps equal in area to that which at present exists above. On this basis 783 per cent. of the original area has therefore been lost. The stone persistently added, aided by the material of crumbling piers, has formed an obstruction across the channel, rising, as our sketch shows, twenty feet above the level of the bottom to the north, and having on its southerly side a slope of two to one-a slope frequently given by engineers to dams. In fact the whole effect of these obstructions across the bed of the stream has strikingly the appearance of dams on a mill stream. To remove so much of the obstruction at Washington bridge as to give a depth of fifteen feet at low water would require the excavation of 7,080 cubic yards of material-presumably stones of various sizes. Each decaying pier, as it fell away into the channel, by diminishing the area of flow, increased the force of the current, which its fellows had to resist, and each stone added to the foundation had to oppose a velocity enhanced by itself,

till, at the present time, the embankment has caused, and shows itself capable of withstanding a current at spring tides of five miles per hour.

Previous to the

The present railroad bridge was built in 1867-8. construction of the present bridge, a bridge built in 1835, and succeeding repairs on it, contributed to the formation of an obstruction at this point. The bridge of 1835 had three pile piers as at first built. In 1857 three more were added at the center of the spans. The draw of 1835 was supported on piles and a platform, "the piles and capping of which still remain." In 1858 the old draw was removed and a new one substituted. "The abutments which were continued as a bank wall above the bridge on the west end, and above and below on the east end, were built of rough stone. No piles were driven, but a thick layer of good brush was carefully strewn on top of the mud, and the foundation stone laid directly on this."

Some of the old piles were removed in 1866, in preparing for the present bridge. This bridge has four piers between the abutments, one of stone, three of piles surrounded with iron cylinders under Cushing's patents. "After the completion of the piers rubble stone was thrown in around and between the cylinders, on top of which was placed about a foot of slag from the puddling furnaces of the iron works. Cotton bags were then filled with oyster shells and thrown in, and on top of these another foot of slag." The bottom of the river at this point is covered with a crust of oyster shells four feet thick, through which the cylinders of the Cushing piers extend six inches. into the soft mud. This fact limits the dredging, which may be safely done on the axis of the present bridge, unless we are prepared to allow the full section of channel which the current would scour in soft mud. The fact that soundings taken previously to the present construction on the axis of the bridge agree quite nearly with those made since, indicates that the work of 1867-8 added but little to the obstruction created in 1835. The area on the axis of the railroad bridge at low water is thirty-eight per cent. of the area with which the corresponding area of Washington bridge was compared.