The rate of progress given in the foregoing Table is very different from what was expected previous to the commencement of the works. It was then anticipated that the tunnel would be excavated from end to end before the close of 1864, but it was not until the 15th of October, 1866, or 9¼ years after operations had been begun, that exactly one-half was perforated. On the 1st November, 1867, the half had been exceeded by 1,958 metres, still leaving 4,152 metres to be excavated. The amount of perforation accomplished on the two sides of the mountain has always been unequal, for of the 4,152 metres yet to be excavated, 2,905, equal to about 1⅞ mile, have to be accomplished on the French side, whilst on the Italian there are two-thirds of a mile. This will be understood by an explanation of the strata through which the tunnel is to be carried. Commencing at Modane, there are 2,140 metres of schist, then 363 of quartz, followed by 2,706 of compact limestone, and finally 901 of schist. This completes one half; the other, or Italian half, is all schist. The only rock comparatively easy in working is the schist, but from the commencement the schist on the French side was of a more resisting character than that on the Italian. The miners came upon the quartz exactly where they expected to find it, but instead of its being a stratum 400 metres thick, as was anticipated, it turned out to be only 363 metres; nevertheless, it required two years, less two months, to bring it into subjection, that is, from the 15th of June, 1865, until the 20th of April, 1867,—the progress forward during all that time, not much exceeding half a metre (about 20 inches) a-day. The compact limestone nearest to the quartz having been partly decomposed by the action of this latter, was very workable. Hence, during May and part of June 1867, the advance was very considerable, but since June the compact limestone has proved to be harder but not so difficult to work upon as the quartz. For six weeks the engineers were hopeful that they could go on at the rate of three metres a-day. If such progress could have been unflinchingly maintained, the excavation on the French side could have been accomplished by August 1870. With two metres a-day it will require until March 1872; but if, the advance do not exceed a metre and a-half a-day for two-thirds of the whole distance, the tunnel cannot be perforated under six years, which brings the date to July, 1873.