THE STORY OF A GREAT WORK.
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there will be a tunnel over twelve thousand feet long and twenty-seven feet in diameter, to accommodate two tracks. The Michigan Southern has also been making tests at its crossing, a short distance below Sarnia, but the strata are not favorable for tunnel construction.
Fig. 7.—Interior of Tunnel.
One of the remarkable features in connection with the St. Clair Tunnel is the rapidity with which it was constructed. The average advance was 455·4 feet per month. Contrast this with the Thames Tunnel, three thousand six hundred feet long, which was commenced in 1825 and not completed until 1843, though work
