=Excavation.=--The tunnel was excavated by the heading method in only two cuts, viz., the heading and bench as indicated in the Fig. 65. The heading, almost as wide as the upper portion of the tunnel section, was excavated in the manner explained on page 91. After the heading was removed, the enlargement of the entire upper section of the tunnel was accomplished by driving three inclined holes at each side of the heading. They were driven at different depths and inclinations, as shown in the figure and were called trimming holes. At the same time the bench was removed by means of five holes--three vertical and two inclined. The line of subgrade was reached by means of five grading holes driven almost horizontal with a slight inclination downward. The air drills for the heading were mounted on columns, all the others on tripods. The blasting was done in the following order: the grading holes were blasted in the first round, the bench and trimming in the second, the center cut of the heading in the third, the sides in the fourth and the dry holes in the last. Thus each advance of 7 ft. of the whole tunnel section was made by means of forty holes fired in five rounds which consumed 277 lbs. of dynamite with an average additional quantity of 76 lbs., making a total of 353 lbs. With the exception of the center cut, where 60% dynamite was used, all the other holes were discharged with 40% dynamite. [Illustration: ~Cross Section.~ ~Longitudinal Section.~ FIG. 64.--Arrangement of Drill Holes in the Fort George Tunnel. FIG. 65.--Longitudinal Section of the Heading and Bench Excavation at the Fort George Tunnel.]