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THE POPULAR SCIENCE MONTHLY. 



Hallet's Point was $81,092.24 ; at Flood Rock it was only 8106,509.93, 

 though the blast was 5*6 times as large. These results together indi- 

 cate 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 sup- 

 plied 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 : 



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 re- 

 duced. 



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), fin- 

 ished 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. Rylandcr's Reef (IG) 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. 



