126 Tl NNKLING 



cliaiMeter to the shaft and to the east portal, and was used for 

 ope rating the hoisting engines as well as the drills at these 

 workings. Inside the tunnel, specially designed derrick cars 

 were employed to handle large stones, they being also operated 

 by compressed air. This car ran on a center track, while the 

 mucking cars ran on side tracks, and it was employed to lift 

 the bodies of the cars from the trucks, place them close to the 

 front, being worked where large stone could be rolled into 

 them, and return them to the trucks for removal. In addition 

 to handling the car bodies the derrick was used to lift heavy 

 stones. The hauling was done at first by horse-power, and 

 later by dummy locomotives. 



Croton Aqueduct Tunnel. In the construction of the Croton 

 Aqueduct for the water supply of New York city, a tunnel 31 

 miles long was built, running from the Croton Dam to the 

 Gate House at 135th St. in New York city. The section of 

 the tunnel varies in form, but is generally either a circular or a 

 horse-shoe section. In all cases the section was designed to 

 have a capacity for the flow of water equal to a cylinder 14 ft. 

 in diameter. To drive the tunnel, 40 shafts were employed. 

 The material penetrated was of almost every character, from 

 quicksand to granitic rock, but the bulk of the work was in 

 rock of some character. The excavation in rock was conducted 

 by the wide heading and bench method, employing the center- 

 cut method of blasting. Four air drills, mounted on two 

 double-arm columns, were employed in the heading. The 

 drills for the bench work were mounted on tripods. Steam- 

 power w r as used exclusively for operating the compressors, 

 hoisting engines, ventilating fans and pumps ; but the size and 

 kind of boilers used, as well as the kind and capacity of the 

 machines which they operated, varied greatly, since a separate 

 power-plant was employed for each shaft with a few exceptions. 

 A description of the plant at one of the shafts will give an 

 indication of the size and character of those at the other shafts, 

 and for this purpose the plant at shaft 10 has been selected. 



