Page:Popular Science Monthly Volume 88.djvu/357

 Popular Science Monthly

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��through treacherous and rotten rock, and has to be built without disturbing the traffic in the present interborough subway, which is to be seen on the second level in the illustration

��perilotis. New underground routes are being driven through some of the world's most crowded streets, and without mate- rially interfering with the traflic. Though the typical construction is a covered ditch with a roof which is only a foot or two below the floor of the street, there are many places where real tunneling and mining operations are rec|uired. The digging goes on under a variety of con- ditions : through imderground swamps and watercourses, through treacherous

��rock, through sand and even through quicksand. At the south end of Man- hattan Island two new sets of tubes are being driven under East River; at the north end a set of tubes was built on shore and then towed out into place and sunk on the bed of the river. In Lex- ington Avenue a new idea in subway l)uilding is i)resented in the form of an underground double-decker. At Grand Central Station the earth is being honey- combed into five k'\els.

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