Note 156 — Chapter IV

The difficulties presented by the stubborn nature of the foundation-wall proved well-nigh insuperable, but, as is observed by Father Greenway,[156] one still more grave awaited the diggers had they succeeded in making their way through. The "concavity" to be excavated within, to contain the large number of powder barrels required for their purpose, would have involved engineering work of the most hazardous kind, and heavily laden as the floor above proved to be, it must, according to all rules of calculation, have collapsed, when thus undermined. But at this juncture, when the wall had been half pierced, a circumstance occurred, not less extraordinary than others we have considered, to change the whole plan of operations.