THE STORY OF A GREAT WORK. 



471 



there will be a tuiinel over twelve thousand feet long and twenty- 

 seven feet in diameter, to accommodate two tracks. The Michi- 

 gan Sonthern has also been making tests at its crossing, a short 





H 



distance below Sarnia, but the strata are not favorable for tunnel 

 construction. 



One of the remarkable features in connection with the St. Clair 

 Tunnel is the rapidity with which it was constructed. The aver- 

 age 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 



