In his later and more important work the same learned historian discusses this question at great length. He analyses all the doubtful pedigrees and origins claimed by the leading clans. Regarding the Fitzgerald theory he says, "But the most remarkable of these spurious origins is that claimed by the Mackenzies. It appears to have been first put forward by Sir George Mackenzie, first Earl of Cromarty," who, in his first manuscript, made Colin a son of the Earl of Kildare, but in a later edition, written in 1669, "finding that there was no Earl of Kildare until 1290, he corrects it by making him son of John Fitz-Thomas, chief of the Geraldines in Ireland, and father of John, first Earl of Kildare, who was slain in 1261." Dr Skene then summarises the story already known at length to the reader, quotes the Record of Icolmkill and the forged charter, and concludes - "The same mistake is here committed as is usual in manufacturing these pedigree charters, by making it a crown charter erecting the lands into a barony. Kintail could not have been a barony at that time, and the Earl of Ross and not the king was superior, for in 1342 the Earl of Ross grants the ten davochs of the lands of Kintail to Reginald, son of Roderick of the Isles, and we find that the Mackenzies held their lands of the Earls of Ross and afterwards of the Duke of Ross till 1508, when they were all erected into a barony by King James the Fourth, who gave them a crown charter. An examination of the witnesses usually detects these spurious charters, and in this case it is conclusive against the charter. Andrew was bishop of Moray from 1223 to 1242 and there was no bishop of that name in the reign of Alexander the Third. Henry de Baliol was chamberlain in the reign of Alexander the Second, and not of Alexander the Third. Thomas Hostarius belongs to the same reign, and has been succeeded by his son Alan long before the date of this charter." Dr Skene adds that if the Earl of Cromartie was not himself the actual inventor of the whole story, it must have taken its rise not very long before his day, for, he says, "no trace of it is to be found in the Irish MSS., the history of the Geraldine family knows nothing of it, and MacVureach, who must have been acquainted with the popular history of the western clans, was equally unacquainted with it." ['Celtic Scotland,' Vol. III., pp. 351-354.]