Hastening then to the Casa Vallejo, Jack found that the sounds of miners at work had been steadily growing more distinct. It was clearly time to prepare his own mine. The gallery extended some six feet beneath the floor of the ruined house adjoining. A heavy charge was laid in it; then the mine was tamped as quickly as possible. All was now in readiness. Through that day Jack scarcely left the place for a moment. It was of the utmost importance that the time for exploding the mine should be well chosen. He dared not run the risk of allowing the French to drive the heads of their tunnels past his own, for indeed they might not pass it, but come clean upon it, in which case they would either explode it themselves, or more probably withdraw the charge. His object was to allow them to approach as near as seemed safe, and then to fire the train. After an anxious day he retired to rest, convinced that a sharp conflict could no longer be much delayed. At ten o’clock next morning, the 8th of February, he judged that the French miners could only be a few feet distant. Withdrawing all his men from the Casa Vallejo to the Casa Hontanon, next door, he waited tensely for a few minutes, then himself fired the train. There was a thunderous explosion, the walls of the room in which he was seemed to rock, then came the crash of falling beams, followed by a death-like silence. The mine had done its terrible work effectually; for the rest of the day there was no further sound of the French. Meanwhile, on the other side of the Ebro the French were gradually preparing for a grand assault. The part of the city along the river bank had been hitherto little damaged, for it was protected by the transpontine suburb of San Lazaro, and to some extent by a few gun-boats moored near the bridge. The key to the position was the Jesus Convent, a building of bricks, with a ditch on the French side of it. The French batteries had made large breaches in its masonry, but in order to carry it by storm it was first necessary for the enemy to trench their way towards it by slow degrees, every step having to be taken under fire from the walls. Their work was delayed for a time by a sudden rise of the river inundating their trenches and driving them back for several hundred yards—a flood hailed with joy by the defenders, who regarded it as another miraculous interposition on the part of Our Lady of the Pillar.