Early reports of large bones from slate mines in the Middle Jurassic rocks at Stonesfield, Oxfordshire are reviewed, along with previously unpublished accounts of the workings. The material that formed the basis for publication of the genus Megalosaurus Buckland and Conybeare, 1824 is documented. The lectotype, a partial right lower jaw, was acquired by Sir Christopher Pegge, Dr Lees Reader in Anatomy at Christ Church, Oxford in 1797. The paralectotype sacrum was acquired by an Oxford undergraduate, Philip Barker Webb, sometime prior to 1814, as revealed by a letter to William Buckland from George Griffin, a Stonesfield well-sinker and mason, in which this specimen is mentioned. Another letter to Buckland from David Oliver, also of Stonesfield, records the discovery of further large bones, and annotations by Buckland indicate their purchase. The reptilian nature of the bones was confirmed during a visit to Oxford by the great French comparative anatomist Georges Cuvier in 1818. The presence of a giant reptile in the Stonesfield Slate became widely known in the English geological community. The six year delay between recognition and publication probably reflects Buckland's other commitments and priorities. Although Buckland largely disappears from the record at the end of 1849, we note one final reference to Megalosaurus in 1854, in the form of a letter to Buckland from Benjamin Waterhouse Hawkins, in which he requests dimensions of Megalosaurus bones to aid construction of the life-sized model of Megalosaurus that can still be seen at Crystal Palace Park in south London.