EAST RIVER AND HELL GATE IMPROVEMENT. 435 



them and Rhinelander's Reef. The two surveying-officers, while agree- 

 ing as to the desirability of removing or mitigating the obstructions, 

 made different recommendations respecting the manner in which they 

 should be dealt with. 



Lieutenant-Commanding Davis recommended that Pot Rock, the 

 Frying-Pan, and Way's Reef be blasted and scattered, and that the 

 Middle Channel be improved by blasting, so as to make a clear chan- 

 nel of sufficient depth for common vessels and steamboats. As the 

 removal of the larger reefs seemed at that time impracticable, he ad- 

 vised that they be faced with sea-walls or piers rising four feet above 

 high water, and provided with spring fenders such as are used at the 

 ferry-docks, so adjusted as to guide vessels coming in contact with 

 them into the channel-ways. Lieutenant-Commanding David Porter, 

 not regarding the deepening of the Middle Channel as practicable, 

 advised that it be filled in with docks, and recommended the removal 

 of a part of the reef at Ilallet's Point. 



No efficient method was suggested for removing the rocks it was 

 proposed to take away, further than to blast them and leave the frag- 

 ments to lie where they might fall, or to be washed away by the cur- 

 rents. This method would obviously make but a slight impression on 

 the larger reefs. 



A process of surface-blasting was first applied by M. Maillefert in 

 185L His method consisted simply in placing upon the rock a charge 

 of gunpowder, usually of 125 pounds, contained in a tin canister, and 

 exploding it by means of the voltaic current. The weight of the 

 water resting upon the charge served to increase the effects of the 

 explosion. No means were provided for removing the broken rock 

 except by breaking it up by successive explosions till it was fine enough 

 to be carried away by the currents. M. l^Iaillefert's operations result- 

 ed, by the use of 620 charges containing 74,192 pounds of powder, at 

 a cost of $13,861, furnished through Mr. Merriam, in removing from 

 the rocks to which they were applied the projecting prominences of 

 small area, but were of little effect when, after reaching the main rock, 

 a considerable extent of surface had to be dealt with. The depth of 

 water was increased, on Pot Rock, from 8 feet to 18-3 feet; on Frying- 

 Pan, from 9 to 16 feet ; on Way's Reef, from 5 to 14 feet ; and on 

 Shell Drake, from 8 to 16 feet. Bald-Headed Billy and Hoyt's Rocks 

 were blown into deep water. The depth on Diamond Reef was but 

 slightly if at all affected, and no effect was produced on Ilallet's Point 

 Reef. In 1852, Congress having appropriated 820,000 for the removal 

 of obstructions, Major Fraser, by Maillefert's method, increased the 

 depth over Pot Rock to 20*6 feet, adding 2-3 feet of water to the 

 18-3 Maillefert had gained, with the expenditure of $6,837. The de- 

 crease in the ratio of returns for expenditure was occasioned by the 

 increased surface of the rock, due to increase of depth. 



In 1856 an advisory council to a commission on the removal of 



