104
Fig. 2. BUILDING A TUNNEL ROOF ON THE SURFACE, A SPECIAL METHOD USED ONLY FOR THE
HARLEM RIVER TUNNEL OF THE NEW YORK SUBWAY.
The finished roof was lowered down on sheet pile side walls, and the tunnel excavated and finished inside tho
protecting box thus formed.
ENGINEERING WONDERS OF THE WORLD.
Borough shown in Fig. 1, wherein they appear,
and also the routes of their land pro-
longations. They form an excellent rapid-
transit network; and if we look into the
future a little optimistically, we may see
further tunnels and new land lines connecting
with them, to form an underground rapid-
transit system commensurate with the exten-
sive street - railway network and the four
north-south lines of elevated railway.
But to turn to the story of the con-
struction of the tunnels. The first tunnel
under the Hudson was completed only in
1903, though it had been begun thirty
Fig. 1.—MAP OF LOWER PART OF MANHATTAN
BOROUGH, NEW YORK CITY, SHOWING ROUTES
OF THE PRINCIPAL TUNNELS AND THEIR LAND
EXTENSIONS.