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The avenige monthly progress in feet of excavating tunnels 

 through treacherous ground may be quite generally assumed 

 to be for: (1) clay of the first variety from 43.4 ft. to 60 ft ; 

 for clay of the second variety from 33.4 ft. to 43.4 ft. ; for clay 

 of the third variety from 23.3 ft. to 33.4 ft, and for quicksand 

 from 30 ft. to 50 ft The monthly progress in feet made in 

 sinking the shafts of the Hoosac and Musconeteong tunnels in 

 America was as follows : 



The average monthly progress of sinking shafts in treach- 

 erous soils may be assumed to be as follows: clay of first 

 variety, 50 ft. to 75 ft ; clay of second variety, 36.75 to 50 ft ; 

 clay of third variety, 23.4 ft to 36.75 ft ; quicksand, 16.7 ft. 

 to 33.4 ft. 



