He had a large staff of workmen under him, and an assistant surveyor, John Oliver, who directed the workmen, measured the masons' work, bought in materials, and examined the accounts; a clerk of the works, Laurence Spenser, who overlooked the men, saw that they did their work as directed, and made up the accounts; each of these was paid 100_l._ a year, half as much as the salary of the architect himself; a clerk of the cheque, Thomas Russell, who called over the labourers three times a day, and kept them to their business. Besides these, there was the master-mason,[142] Thomas Strong, the master-builder of S. Stephen's, Walbrook, frequently employed by Wren, and the master-carpenter, Richard Jennings; all were carefully chosen, and were devoted to Sir Christopher, whose great genius, gentle disposition, and steady equable mind made him much beloved and respected. On June 21, 1675, the first stone of S. Paul's was laid by Sir Christopher and his master-mason, not by King Charles, as is sometimes said.[143] In the previous year Wren had lost his son Gilbert, who was buried in S. Martin's on March 23. In the February following another son was born and baptized by the name of Christopher. This son survived his father and began the collection of letters, papers, and miscellaneous facts about the Wren family which was afterwards published under the name of 'Parentalia; or, Memoirs of the Wrens.' It is, in truth, little but a heap of materials amongst which each fact has to be sought for and its proper place ascertained. [_EXCAVATIONS._] It has been truly said that the accounts of the building of S. Paul's are meagre in the extreme. A little is, however, known. As Wren had foretold, there was much 'to be done in the dark;' the old foundations were not to be trusted, and immense excavations had to be made. In the course of this work, he discovered 'graves of several ages and fashions, in strata or layers of earth, one above another, from the British and Roman times.' The 'Parentalia' describes 'a row of Saxon graves, the sides lined with chalk stones, below were British graves, where were found ivory and wooden pins of a hard wood, seemingly box, about six inches long; it seems the bodies were only wrapped up and pinned in woollen shrouds, which being consumed the pins remained entire. In the same row and deeper were Roman urns intermixed.'