Popular Science Montlily

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��while to the air, it can be crumpled in the hand like earth.

^^'hen New York built its first sub- way, the engineers encountered some of this "rotten rock" in Park Avenue near the Grand Central Station. Serious slides resulted ; houses caved in. And the builders of the new subways have not come off anv more fortunatelv than

���Rebuilding and moving sewers to vacate space required for the new subways. The sewers alone mean an ex- penditure of from six to seven million dollars. The illustration shows a large tube making a new outlet for the sewer system emptying into the Hudson River. This outlet will cost the city half a million dollars. To the left of the picture is the magnificent new Pennsylvania Terminal

��their predecessors. Of several cave-ins the most serious recently was one in Seventh Avenue, near Twenty-fourth Street, where seven persons were killed and eighty-five were injured.

Try to conceive, then, how cautiously the engineers must work in building the Lexington Avenue double-decker sub- way and in tunneling the treacherous rock in the vicinity of Grand Central Station where ( as an accompanying illustration tells better than whole pages of description could doj the ground is being honey- combed into five levels — this in the same perilous ground where the engineers first learned how gingerly they must proceed in a local- ity where the "rotten rock literally abounds. And to- day an extra factor of difti- culty must be confronted here from the fact that the operation of the present subway cannot be interfered with while the new tubes are being constructed.

Following a blast, a slide of "rotten rock" knocked out the shoring of the wood- en bridge which forms the temporary street, and en- gulfed a loaded street car, a large motor truck, and scores of pedestrians. Spec- tators said that the structure fell like a house of card.-. The maze of gas pipes and electrical conduits added a grave danger, for a spark from the tangled wires would have exploded the leaking gas, and would have added many more names to the list of killed and injured. On Saturday, of the same week, a section of Broadway fell in, endangering many lives. Fortunately, there were few pedestrians in that section of the street and only one vehicle, a taxicab. so that the casualties were few. lUit New York's confidence was sadly shaken.

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