They had descended into the third compartment; they had arrived at the stone which walled the outlet.

Porthos seized this gigantic stone at its base, applied his robust shoulder, and gave a heave which made the wall crack.

A cloud of dust fell from the vault, with the ashes of ten thousand generations of sea birds, whose nests stuck like cement to the rock.

At the third shock the stone gave way, and oscillated for a minute.

Porthos, placing his back against the neighboring rock, made an arch with his foot, which drove the block out of the calcareous masses which served for hinges and cramps.