“ In the construction of railroads it is frequently necessary to pierce the hills, so as to preserve a line of road as nearly level as practicable. The method of proceeding with tunneling depends mainly upon the kind of material to be excavated. This having been generally ascertained by borings and trial shafts, the work is commenced by sinking the working shafts, which must be sufficiently capacious to admit readily of lowering men and materials, raising the material excavated, fixing pumps, and also for starting the heading of the intended tunnel when the required depth is reached. ”