So much for the evidence as to the actual hymns in use from sources available at the period when the _Later Hymnal_ flourished. The origin of the _Later Hymnal_, however, is far from clear. It has been defined as a collection arising about the seventh century which superseded the _Old Hymnal_ and has since prevailed.[22] This opinion advanced by Blume and affirmed by Walpole, depends upon the theory that the later cycle had been in use in the British Isles since the period of Gregory the Great. An Anglo-Irish cycle therefore, was posited which took possession of the continent, usurping the original Benedictine hymnal. As early as 1911, Blume’s theory was questioned by Wilmart, the Benedictine scholar, who asserted that the early cycle constituted a Gallican hymnal only,—a possibility mentioned above. He thought that the _Later Hymnal_ was a new version of the Benedictine cycle representing a normal growth through the centuries. Other critics of note have adopted one or the other viewpoint, Frere following that of Blume; and Raby, that of Wilmart.[23] A final solution is obviously impossible for lack of manuscript evidence. At the accession of Charlemagne, 768, the future of liturgical hymnody was uncertain as the forces of Roman usage and Benedictine practice were in conflict and the possibility of transferring the Benedictine heritage to the church extremely doubtful, as the preceding survey has already made clear. Secondary forces, however, were at work to achieve this very end. First, the early gains made in compiling the Gallican Hymnal and extending it to the secular clergy were never entirely lost. A precedent had been set. Second, the Benedictine cycle was enjoined wherever the Rule was effective and its use was further stimulated by royal capitularies upon the subject of music and singing. Third, the establishment of monastic centers of music in the leading Benedictine abbeys was productive of literary as well as musical effort, attested by the very manuscripts of hymn collections gathered there. The manuscripts of St. Gall, for example, cover every department of contemporary medieval hymnology.