718 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



Here it was necessary to go through 215 feet of overlying earth 

 before coming to the rock. The caisson method had to be resorted 

 to, and the caisson was sunk over 100 feet below the water line before 

 rock was reached. Considerable difficulty was here experienced in 

 sinking the shaft to the rock, because it called for the use of pneu- 

 matic pressure that taxed the endurance of the workmen to the limit. 

 From here on the water will be conducted through pipes laid in a 

 trench of a moderate depth below the surface. From the foot of 

 Seventy-ninth Street, Bay Eidge, the conduit will be run across the 

 Narrows to Staten Island, through a pipe 36 inches in diameter, pro- 

 vided with flexible joints, and laid in a submarine trench. The 

 details of this section of the work have not yet been given out. How- 

 ever, tests have been made to discover at what depth the pipe line 

 under the water must be buried. It is evident that it must lie far 

 enough below ground to prevent its being entangled with anchors 

 from large vessels that may have to anchor in the Narrows. The 

 matter has been thoroughly investigated, and practical tests have 

 been made by dragging anchors of large size along the bottom. It 

 has been determined that if the pipe line is buried at least 8 feet 

 under the bed, it will be entirely safe. On the Staten Island side a 

 48-inch pipe will carry the water on up the hill and through a tunnel 

 into Silver Lake Reservoir, 120 miles from the source in the Catslrills. 

 The greatest interest in this city section of the aqueduct attaches 

 naturally to that part which is being excavated through solid rock 

 under the busy city. It is a surprising fact that a work of such 

 magnitude can be carried on directly under our feet without incon- 

 veniencing us in the least. The only surface evidence of the deep 

 rock tunneling is to be found at the various shafts which are located 

 in parks or public squares. The principal difficulty that presented 

 itself at first was the question of storing explosives for a work of 

 such great proportions. To keep the necessary explosives on the sur- 

 face was to harbor constant menaces to the lives of the citizens. The 

 matter was finally solved by placing the dynamite magazines far 

 under the surface in the rock, and setting the doors to these maga- 

 zines so they will automatically close in case of an explosion and trap 

 the hot and poisonous fumes in the rock chamber, where they can do 

 no harm to the workmen. The idea was borrowed from European 

 practice, where mining operations are conducted close to and some- 

 times directly under large cities. Access to the dynamite chamber 

 is had through a zigzag drift. At each turn of the drift a pocket is 

 excavated, and the chamber itself is made of large capacity. In this 

 chamber the dynamite is stored under a protecting roof to keep off 

 any fragments of rocks that might fall when jarred by the " shoot- 

 ing " in the tunnel. At the entrance of the drift a very substantial 

 concrete bulkhead is built, and in this is a low doorway. The door is 



