His most important contribution to literature is the Annals of Scotland, of which the first volume, “From the accession of Malcolm III., surnamed Canmorβ, to the accession of Robert I.,” appeared in 1776, and the second, “From the accession of Robert I., surnamed Bruce, to the accession of the House of Stewart,” in 1779. It is, as Dr Johnson justly described this work at the time of its appearance, a “Dictionary” of carefully sifted facts, in our language a new mode of history which tells all that is wanted and all that is known, but without any laboured splendour of language or affected subtlety of conjecture. The other works of Lord Hailes include Historical Memoirs concerning the Provincial Councils of the Scottish Clergy (1769); An Examination of some of the arguments for the High Antiquity of Regiam Majestatem (1769); three volumes entitled Remains of Christian Antiquity (“Account of the Martyrs of Smyrna and Lyons in the second century,” 1776; “The Trials of Justin Martyr, Cyprian, &c.,” 1778; “The History of the Martyrs of Palestine, translated from Eusebius,” 1780); Disquisitions concerning the Antiquities of the Christian Church (1783); and editions or translations of portions of Lactantius, Tertullian, and Minucius Felix. In 1786 he published An Inquiry into the Secondary Causes which Mr Gibbon has assignedfor the Rapid Growth of Christianity, a Dutch translation of which was published at Utrecht in 1793. Both by its acuteness in detailed argument and by its freedom from theological rancour this controversial work is entitled to rank as one of the most respectable of the very many replies which were made to the famous 15th and 16th chapters of the Decline and Fall of the Roman Empire ; but it has too much the character of a collection of detached critical remarks. A “Memoir” of Lord Hailes is prefixed to the 1808 reprint of his Inquiry into the Secondary Causes.