CHAPTER V

BRIDGES 56

Bridges of timber, then stone, then steel--The Starucca Viaduct--The first iron bridge in the United States--Steel bridges--Engineering triumphs--Different types of railroad bridge--The deck span and the truss span--Suspension bridges--Cantilever bridges--Reaching the solid rock with caissons--The work of "sand-hogs"--The cantilever over the Pend Oreille River--Variety of problems in bridge-building--Points in favor of the stone bridge--Bridges over the Keys of Florida.