TUNNELS

underground pa ages cut through rock or soil to serve as subterranean channels of communication on railway or highway routes, or as arteries for carrying water (aqueducts). When built near the surface by the cutand-cover method in a railway project they are known as subways (g.v.). Cut in deeper levels for local transit, as in London and under the Hudson river, they are called ‘tubes,’ (tubular railways). The most notable rock tunnels are built through the Alps, Switzerland, namely, the Simpton (12.3 miles long), the St. Gothard (9.7 miles) the Loetschberg (9 miles), and the Alberg (6 miles). On the American continent a tunnel cuts through the Andes between Argentina and Chile for four miles, a similar mountain tunnel is the Cascade, 2.6 miles long, in the State of Washington. Among the earliest American tunnels is the Hoosac in Ma achusetts, 4.75 miles long. In rock tunneling the rock is blasted by dynamite charges placed in holes drilled for the purpose, as in quarrying. Metheds of soft-ground tunnelling depend on soil stability. Roof supports are a nece ity, held up by frames and posts as the work proceeds. The cutting shield, used for tunnelling under rivers in conjunction with compre ed air, is a powerful cylinder, 10 to 20 feet long, equipped with hydraulic jacks to drive it forward after enough space has been cleared in front by face work, ‘and as the cutting proceeds cast iron sections of lining in rings are set. Among important soft-earth tunnels are a number cut under the Thames, Seine, and Hudson and East rivers (New York), the St. Clair and Michigan Central tunnels, Detroit, the street tunnels at Glasgow harbor and Black wall (London), and the East Boston trolley tunn els. A Western hydro-electric project in California matured in 1923 for the construction of a tunnel system of 86 miles through mountains for the diversion of water from higher to lower jevels. The longest tunnel, the Florence Lake, is thirteen miles long and taps the great watersheds lying between the Kaiser and Minaret Ranges to convey their flow to generating power plants 11,000 feet below the point of intake. In 1923 a pair of vehicular tunnels were in progre of construction under the Hudson river, 60 feet below mean low tide, connecting New York City and Jersey City. They are 9,250 feet in length. ‘Their purpose is to relieve congested ferry traffic of pa enger bearing and freight vehicles and to afford better transportation of merchandise, foodstuffs and coal from the mainland direct to destination in Manhattan, the Bronx and Long Island.;