At first the idea was entertained of restoring the ruins, but this was finally abandoned by royal warrant to the Commissioners in 1668, and clearing and excavations began. The workmen with pickaxes stood on the top of the walls some eighty feet high, and others below cleared away the dislodged stones--a dangerous task in which lives were lost. Of the Central Tower some two hundred feet remained, and a more expeditious plan was adopted. A deal box, containing eighteen pounds of gunpowder, was exploded level with the foundations at the centre of the north-west pillar, and the adjacent arches were lifted some nine inches, while these ruins "suddenly jumping down, made a great Heap of Ruin in the Place without scattering." Wren estimated the whole weight lifted at three thousand tons, and the labour saved equal to that of a battalion of a thousand men. When the alarmed inhabitants of the neighbourhood heard and felt the concussion, they naturally took it for an earthquake. In the surveyor's absence a subordinate used too much powder in attempting a second mine, and neither burying it low enough nor building up the mouth, a stone was projected through an open window into a room where some women were sitting at work. Although no one was hit, the neighbours took alarm, and successfully agitated against all further blasting. Delay was caused, and finally a battering-ram some forty feet in length, worked by thirty men, completed the demolition. The stones and rubbish were cleared away, and used in different buildings and in repairing the streets. Afterwards some houses on the north side which encroached on the building, and may have been those that assisted the passage of the Fire, were levelled, and their site included in the churchyard.
When at length the ruins of Old St. Paul's had come down and the huge mass of wreckage been cleared away, working from the west the excavations for the new foundations were begun. The old cathedral had rested on a layer of loam, or "pot earth" or "brick earth," near the surface; and wells being sunk at various points to ascertain the depth of this, it was found that the loam, owing to the ground sloping towards the south, gradually diminished from a depth of six feet to four. Sinking further, they found sand so loose as to run through the fingers; next, freshwater shells and more sand, and continuing through hard beach or gravel, they reached at last the London clay.[58] At one point of the north-east corner, where the loam had been dug out, Wren was compelled to rest the foundations on the clay; and it seems almost a pity that this was not universally adopted, at whatever additional cost of time and labour, in preference to the loam. The building had not long been completed ere the great weight of the dome caused some of the piers to sink from an inch to more than two inches, and Edward Strong the younger had to repair cracks and fissures.[59] Dean Milman tells us that in his time the City authorities once contemplated a sewer on the south side; but the surveyor, Mr. R. Cockerell, remembering that the sand and shells underneath the loam would be in danger of oozing out, went in great haste to him, and on their joint representation the project was abandoned.