From Antonia Fraser's'mary Queen of Scots'...
'Once more, however, the repose of the queen of Scots was destined to be disturbed. In 1867 a search was instituted by Dean Stanley within the royal tombs of Westminster Abbey for the body of James I, whose position was unrecorded. It was eventually discovered in the tomb of Henry VII, the first Tudor and the first Stuart monarch of England lying appropriately together with Elizabeth of York, the woman who had made the foundation of both dynasties possible. But in the course of the search, among the places it was thought he might have appropriately chosen for his own sepulchre was the tomb of his mother. An entry was made below the monument to Mary, and at the foot of an ample flight of steps marked WAY was found a large vault of brick, twelve feet long, six feet high and seven feet wide. A startling and harrowing sight greeted the gaze of the Victorian searchers: the queen of Scots was far from lying alone in her tomb. A vast pile of lead coffins rose upwards from the floor, some of them obviously of children, some so small as to be of mere babies, all heaped together in confusion, amid urns of many different shapes, which were scattered all through the vault.
It was discoverd that Mary shared her catacomb with numbers of her descendants, including her grandson Henry, Prince of Wales, who died before his prime, her granddaughter Elizabeth of Bohemia, the Winter Queen, and her great-grandson Prince Rupert of the Rhine, amongst the most romantic of all the offshoots of the Stuart dynasty. Most poignant of all were the endless tiny coffins of the royal children who had died in infancy: here were found the the first ten children of James II, and one James Darnley, described as his natural son, as well as the eighteen pathetic babies born dead to Queen Anne, and her sole child to survive infancy, the young Duke of Gloucester.'