INDUSTRIAL PROGRESS DURING THE YEAR 1875. ccxlv 



tances circular galleries have also been cut across the head- 

 ings, forming a series of columns or # piers at the points of 

 intersection, by which the roof is supported. The work of 

 demolishing the reef will consist in breaking up these piers 

 and shattering the rocky roof. The boring of holes in the 

 roof and the columns has been progressing for some months, 

 a number of Burleigh rock-drills being employed for that 

 purpose. Captain Heuer expects to complete the drilling 

 about the last of January. The work of charging will then 

 be commenced, and will probably occupy two months longer. 

 The nitro-glycerine, which will be used for the explosion, will 

 be placed in iron tubes, each of which will have a direct bat- 

 tery-connection, besides being connected with adjacent holes 

 by means of a series of smaller tubes filled with the same 

 explosive. When all is ready the water will be let into 

 the excavation, and the whole series of charges exploded 

 simultaneously by electricity. It is proposed to fire the 

 mine on the Fourth of July, 1876. 



At Flood Rock, likewise, the work of excavation was com- 

 menced last June. The same system will be pursued as at 

 Hallett's Point, but the excavations will be much greater in 

 extent, as the rock stretches out about 400 feet in two di- 

 rections from the shaft. At the time we write, a shaft ten 

 by forty feet in plan, and sixty feet deep, has been sunk, 

 from the bottom of which tunnels will radiate until the 

 whole reef shall have been undermined. Thus far but two 

 tunnels have been started, which are in about twenty feet 

 and thirty feet respectively. Only a commencement has 

 been made, the survey being as yet incomplete. The reef em- 

 braces over six acres of area, and the time necessary to com- 

 plete the work will depend entirely upon the action of Con- 

 gress in making appropriations. The removal of the reef at 

 Hallett's Point will materially lessen the dangers of the Hell 

 Gate passage, and be a permanent advantage to commerce 

 even before the second and more difficult enterprise is 

 brought to a sucessful conclusion. 



The government w T orks at League Island Naval Station 

 are being rapidly advanced. The buildings already erected, 

 but not yet finished, are the Iron-plating shop, 270 by 85 

 feet, and w T hich will be connected w r ith the Naval Con- 

 structer's Department, and the Yards and Docks Building. 



