In the erection of the lighthouse itself, the first important operation, and one which occupied the whole of the season of 1839—from the 6th of May to the 30th of September—was the excavation of a suitable foundation. When building the Eddystone, Mr. Smeaton had been compelled to take into consideration the peculiar structure of the rock, and to adapt his lower courses of masonry, as we have seen, to a series of gradually ascending terraces formed by the successive ledges of the rock itself. This difficult and expensive process was rendered unnecessary by the geodesical formation of the Skerryvore. Mr. Stevenson, therefore, began work by hollowing out a base of forty feet diameter—the largest area he could obtain without any change of level. This portion of his enterprise occupied twenty men for two hundred and seventeen days; two hundred and ninety-six charges of gunpowder were made use of; and two thousand tons of débris and refuse were cast into the sea. The mining or blasting operations were not carried on without great difficulty, on account of the absence of any shelter for the miners, who were unable to retire more than ten or twelve paces, at the furthest, from the spot where the charge was fired. The quantities of gunpowder, therefore, were measured with the utmost nicety; a few grains too many, and the whole company of engineers and workmen would have been blown into the air. Mr. Stevenson himself generally fired the train, or it was done under his superintendence and in his presence; and from the precautions suggested by his skill and prudence, happily no accident occurred. During the first month of their residence in the barrack, he informs us[45] that he and his men suffered much inconvenience from the inundation of their apartments. On one occasion, moreover, they were a fortnight without receiving any communication from the mainland, or from the steam-tug attached to the works; and during the greater part of this time they saw nothing but white plains of foam spreading as far as the eye could reach, and the only sounds were the whistling of the wind and the thunderous roar of the billows, which ever and anon swelled into such a tumult that it was almost impossible to hear one another speak. We may well conceive that a scene so awful, with the ruins of their first barrack lying within a few feet of them, was calculated to fill their minds with the most discouraging apprehensions. Mr. Stevenson records, in simple but graphic language, the indefinite sensations of terror with which he was aroused one night when a tremendous wave broke against the timber structure, and all the occupants of the chamber beneath him involuntarily uttered a terrible cry. They sprang from their beds in the conviction that the whole building had been precipitated to the depths of ocean. [45] A. Stevenson, “Account of the Skerryvore Lighthouse,” p. 143.