250 



ENGINEERING. 



far enough out to prevent the bottom from be- 

 ing scoured out below the screen. The total 

 width of the revetting is usually about 100 

 feet. The portion which is carried out into 

 the river is sometimes anchored with pieces of 

 rock ; but usually it is held in place by the ac- 

 tion of the current, and is soon imbedded under 

 a deposit of sediment. The varieties of revet- 

 ment which have given the best satisfaction 

 are the brush-blanket, in which the brush 

 is bound together to form a mat with wire; 

 the woven brush revetment ; and the willow 

 screen, in which the willows are bound close 

 together with wire, instead of at a distance 

 apart, as in the willow curtain. Where the 

 bank is protected with revetting, instead of 

 being worn away by the current, a deposit of 

 sediment forms on the screen which drives the 

 current farther and farther out. The cost of 

 these protective screens is $2.25 to $2.50 a 

 foot, measured along the bank. The brush- 

 dikes cost $1 a running foot. 



The removal of Flood Rock in Hell Gate, 

 the entrance to New York Harbor from Long 

 Island Sound, will widen the channel from 600 

 feet, its present width, to 1,200 feet. About 

 three acres had been undermined and were 

 ready to be blasted in August, and between 

 five and six acres remained to be excavated. 

 The clearing away of this obstruction will en- 

 able the largest ships to enter the East River, 

 giving from 26 to 32 feet of water at low tide 

 through this channel. The velocity of the 

 tide will probably be increased by the de- 

 struction of this reef. There were over two 

 miles of galleries, four or five feet broad and 

 seven feet high, excavated at the beginning 

 of December, and 783,000 feet of rock taken 

 out, more than the whole excavations at Hal- 

 let's Reef. The entire reef is to be blown 

 up with a single blast, in which over 200,000 

 pounds of the highest explosives will be used. 

 There are ten tunnels, already 600 feet long, 

 running parallel with the current. The tunnel- 

 ing progresses at the rate of 500 feet a month. 

 The excavations are approached through a 

 shaft, sunk from the crown of the rock, and 60 

 feet deep. The top of the reef is below the 

 high-water line, and to sink the shaft a coffer- 

 dam had to be used. With the excavated ma- 

 terial an island was built up on the surface of 

 the rock, upon which stand a blacksmith's and 

 repairing shop, a boiler-house, etc. The final 

 explosion will probably take place about the 

 middle of the year 1883. 



The removal of Diamond Reef in New York 

 Harbor, situated midway between the Battery 

 and Governor's Island, a serious obstruction to 

 navigation, which received its name from the 

 wreck of the ship Diamond upon it, was com- 

 pleted on the 9th of July. The excavation of 

 this large and dangerous rock was accom- 

 plished by means of the drilling scow invented 

 by General Newton for submarine mining. 

 (See HELL GATE IMPROVEMENTS in "Annual 

 Cyclopedia" for 1876.) Diamond Reef was 



entirely submerged, and was about four acres 

 in extent. The surface - blasting system for 

 submerged rocks proposed by Mailleftrt was 

 tried upon this reef; and before him other 

 contractors had attempted to clear it away, 

 but abandoned the undertaking. These at- 

 tempts were made under the authority of the 

 city government, which entertained the plan 

 also of building up the reef into a visible 

 island. The average depth of the holes drilled 

 by the rods of the drilling scow was 10 or 12 

 feet below the surface of the rock. As many 

 as 21 holes, charged with 1,140 pounds of ni- 

 tro-glycerine, were sometimes fired in a single 

 blast. A part of the material of the reef con- 

 sisted of deposits of glacial clay, pebbles, and 

 bowlders. General Roy Stone, the superin- 

 tendent of the work under General Newton, 

 employed an hydraulic jet for removing this 

 lighter matter, and the deposits of silt and har- 

 bor rubbish which overlaid it and the surface 

 of the rocky portions of the reef. Where the 

 rock was not homogeneous, but was mixed 

 with the clay and loose pebbles, boring with 

 the scow was impracticable, and some device 

 like this method of hydraulic mining was ne- 

 cessary. Powerful streams of water with a 

 pressure of 150 pounds per square inch were 

 projected upon the surface, when consisting of 

 soft material or mixed hard-pan and detrital 

 matter, which penetrated the mass at the rate 

 of a foot a minute, producing a hollow three to 

 five feet in diameter, in which bowlders of 

 20 pounds' weight would be suspended by the 

 force of the stream. The cost of removing 

 the reef by these methods amounted to only 

 $309,400. 



Appropriations have been voted by Con- 

 gress to survey a route for connecting the 

 Hudson and East Rivers above Manhattan Isl- 

 and by a navigable channel. The projected 

 canal is to be 18 feet in depth, allowing the 

 tide to pass freely from one river to the other, 

 and from 350 to 400 feet wide. The survey 

 has been conducted by General John Newton. 

 The beds of Harlem River and Spuyten Duy vil 

 Creek will be utilized. The canal is to start 

 on the east side at the mouth of Harlem River, 

 which it follows as far as Dyckman's Meadows, 

 where it turns westward to join Spuyten Duy- 

 vil Creek, a cutting having to be made through 

 a ledge of rocks and through dry ground for 

 some distance beyond. The route then fol- 

 lows the creek to its mouth, considerable rocky 

 excavation having to be made in its bed. Such 

 a passage would save vessels going to New Eng- 

 land with freight taken on in the North River, 

 the distance around the Battery, about 24 

 miles, and would relieve the crowded rivers to 

 the extent of this traffic. The cost of the im- 

 provement is estimated at $2,000,000. 



The French Paris-New York Telegraph Com- 

 pany, which has lately laid a cable across the 

 Atlantic, is the fourth transatlantic cable line 

 which has been established. The three others 

 are in operation, but have all been brought 





