SUBTERRANEAN RIVER WALKER AND BOND. 719 



of massive construction, built of I-beams, 16 inches deep and spaced 

 apart with oak beams 12 inches square. The door has beveled edges, 

 so that it will seat itself snugly in the doorway. The door is always 

 kept open at an angle of about 45°. In the magazine a thousand 

 pounds of dynamite may be kept at a time. Should this be exploded, 

 the explosion wave would have to travel down the zigzag passage and 

 would lose much of its force at each abrupt turn, finally striking the 

 door with gi'eatly diminished energy. The door would be slammed 

 shut by the blast of air issuing from the drift and would then be held 

 shut by the gases of the exploded dynamite. A magazine of this 

 sort has been constructed near the foot of each shaft — not at the foot, 

 however, for fear that in case of a mishap, it might block the escape 

 of the men. The magazines have been tested by exploding a number 

 of sticks of dynamite around the first bend in the drift, and in every 

 case the door has closed just as expected. 



The work through the rock is being pushed very rapidly; at some 

 of the shafts between 800 and 1,000 pounds of dynamite have been 

 used daily. Within the last year millions of pounds of dynamite 

 have been exploded under the city, while most of New York was 

 totally oblivious to the fact. Already a number of the tunnel sec- 

 tions have been "holed" through. To expedite the work, one con- 

 tractor is using an interesting form of shoveling machine, built 

 especially for this work, so that it may be taken down the compara- 

 tively narrow shaft and be assembled to work within the small 

 diameter of 11 feet, which is the size of the tunnel at the particular 

 point where this machine is now being used. A photograph of this 

 machine is shown herewith, and also a drawing illustrating the mech- 

 anism (pi. 10). The machine is controlled by a single operator and 

 does the work of six laborers. It is provided with a double shovel A and 

 B. The section A digs up the rock and throws it upon the scoop B^ 

 which in turn empties its load upon a traveling chain conveyor C ; 

 the latter delivers the load into muck cars at the back of the shovel- 

 ing machine. The letters B^ 5% 5% and B^ show the successive po- 

 sitions of the scoop. The forward section A is carried upon a crank 

 shaft Z>, which is revolved through the arc indicated by the arrow. 

 Another arrow line shows the course of the front edge of the section 

 A. The forward end of the scoop B rests upon the heel of the sec- 

 tion A, while its rear end is mounted upon a shaft E^ which travels 

 in a guideway F. The forward section A is connected to the shaft E 

 by means of side plates, indicated by dotted lines, so that as the 

 crank shaft D revolves, the slide shaft E is obliged to run up the 

 ways F, as indicated by the letters -fi'^ E^, and E^. The section B 

 is equipped with a small arm G^ which carries a roller that is adapted 

 to engage the cam groove ZT, causing the scoop B to turn over as 

 indicated in the dotted view 5^, and empty its load upon the travel- 



