As a memorial of a usage almost universal in the earlier ages of the church, the _Diptych_, commonly called the _Livre d'Ivoire_, is a valuable relic. The covers exhibit figures of St. Peter and of some other saint, in a good style of workmanship, perhaps of the lower empire. The book contains the oaths administered to each archbishop of Rouen and his suffragans, upon their entering on their office, all of them severally subscribed by the individuals by whom they were sworn. It begins at a very early period, and finishes with the name of Julius Basilius Ferronde de la Ferronaye, consecrated Bishop of Lisieux, in 1784. In the first page is the formula of the oath of the archbishop.--"Juramentum Archiepiscopi Rothomagensis jucundo adventu receptionis suæ.--Primo dicat et pronuntiet Decanus vel alius de Majoribus verba quæ sequentur in introitu atrii;--Adest, reverende pater, tua sponsa, nostra mater, hæc Rothom. ecclesia, cum maximo gaudio recipere te parata, ut eam regas salubriter, potenter protegas et defendas.--Responsio Archiepiscopalis;--Hæc, Deo donante, me facturum promitto.--Iterum Decanus vel alius;--Firma juramento quæ te facturum promittis.--Ego, Dei patientia, bujus Rothom. ecclesiæ minister, juro ad hæc sancta Dei evangelia quod ipsam ecclesiam contra quoslibet tam in bona quam in personas ipsius invasores et oppressores pro posse protegam viriliter et defendam, atque etiam ipsius ecclesiæ jura, libertates, privilegia, statuta et consuetudines apostolicas servabo fideliter. Bona ejusdem ecclesiæ non alienabo nec alienari permittam, quin pro posse, si quæ alienata fuerint, revocabo. Sic me Deus adjuvet et sancta Dei evangelia." The oath of the bishops and abbots was nothing more than a promise of constant respect and obedience on their parts to the church and archbishop of Rouen. You will find it in the _Voyages Liturgiques_[121]; in which you will also meet with a great deal of curious matter touching the peculiar customs and ceremonies of this cathedral. The different metropolitan churches of France before the revolution, like those of our own country prior to the reformation, varied materially from one another in observances of minor importance; at the same time that their rituals all agreed in what may be termed the doctrinal ceremonies of the church. The last manuscript which I shall mention, is the only one that is commonly shewn to strangers: it is a _Graduel_, a very large folio volume, written in the seventeenth century, and of transcendent beauty. Julio Clovio himself, the Raphael of this department of art, might have been proud to be considered the author of the miniatures in it. The representations of lapis lazuli are even more wonderful than the flowers and insects. The whole was done by a monk, of the name of Daniel D'Eaubonne, and is said to have cost him the labor of his entire life.