Hallet's Point was $81,092.24; at Flood Rock it was only $106,509.93, though the blast was 5· 6 times as large. These results together indicate that a great advance has been gained in the economy with which the whole work was carried on; and the progress with the dredging gives promise that an 18-foot channel, 400 feet wide, over the worst part of the reef, may be cleared out by spring. If the funds are supplied as needed, the dredging can all be completed in three years.
The accounts of the observations of the shock of the explosion, have been tabulated by General Abbott, as follows:
| STATION. | Distance in miles. |
Interval of transmission. |
Velocity in miles per second. |
| West Point, N.Y. | 42·34 | 10·9 | 3·88 |
| Hamilton College, N.Y. | 45·0 | 3·88 | |
| Pearsall's, L.I. | 16·78 | 6·6 | 2·54 |
| Bay Shore, L.I. | 36·65 | 13·0 | 2·82 |
| Patchogue, L.I. | 48·52 | 15·4 | 3·15 |
| Goat Island, R.I. | 144·89 | 58·8 | 2·46 |
| Harvard Observatory, Cambridge, Mass. | 182·68 | 19·8 | 0·83 |
| Princeton, N.J. | 48 | 251·0 | 0·94 |
It seems that the speed of the oscillation-wave is the greatest through an uninterrupted rock formation.
Fig. 13 is a bird's-eye view of the reefs of Hell Gate, taken from a model constructed from the preceding map and from surveys of the Engineer Department. The white margin around the shores and reefs represents the parts between mean low water and twenty-six feet below it, the level to which all reefs obstructing navigation are to be reduced.
Negro Point (1): on this reef no work has been done. It is to be undermined and cut off on a line with the Sound-entrance wharf. Holmes Rock (2) and Hog-Back (3) are simply to be finished with a sea-wall. Frying-Pan (4) has been reduced to the level of twenty-four feet below mean low water. Way's Reef (6), Shell Drake (7), finished to the full depth of twenty-six feet. Hallet's Point (8), the rock shattered by the explosion has been entirely removed to the depth of twenty-six feet. The projecting point has been cut off, as shown by Fig. 3. Heel-Tap (9), broken to twenty-six feet, dredged to twenty-two feet, to be cleaned to full depth. Great Mill Rock (10), Little Mill Rock (11), connected by a dike; nothing further to be done here. The Gridiron (12), Flood Rock (13), Hen and Chickens (14), Negro Heads (15), broken to thirty feet; 15 is now being removed to open the Middle Channel at once, and the balance afterward to full depth. Rylander's Reef (16) to be embanked. Bread and Cheese (17) has already been embanked. Scaly Rock (18) has been removed.
It will be readily understood from the above description what has been contemplated by these improvements, how far they have already been carried out and what purpose they have served, and how adequate will be the channel after they are completed.
