[NOTE: Please note that this pertains to the Gallican liturgy, not the Neo-Gallican]
From the letters falsely attributed to St. Germain of Paris, and from several sacramentaries, there can be constructed a description of how a Solemn Mass of the Gallican Liturgy was celebrated in the seventh or eighth century. The bread and wine were prepared before the Mass. An antiphon was sung as the celebrant entered. He read a brief exhortation to the congregation, and, after the deacon had proclaimed silence, he greeted the people with: Dominus sit semper vobiscum. Upon their response, Et cum spiritu tuo, a collect was said.
Three canticles were then sung: the Trisagion, the Kyrie eleison, and the Benedictus. There were three lessons from the Scriptures -- one from the Old Testament, another from the Epistles, and the third from the Gospels. After the Epistle, the canticle Benedicite omnia opera with a responsory was sung. The Gospel was proceded by a procession to the ambo, during which a candelabrum having seven lighted candles was carried and a clerk sang the Trisagion. The same ceremony was observed on the return from the ambo. After the Gospel and a homily, the litany was chanted by the deacon. This ended, the catechumens were dismissed.
The Mass of the Faithful began with the Great Entrance. While the choir sang, the oblata were brought in with great solemnity, the bread in a tower-shaped vessel and the wine already in the chalice. Water was now added to the wine and the oblata were again covered with a veil. The singing of the Laudes ended this ceremony.
After an invitatory addressed to the people, the celebrant recited a prayer. The diptychs (or list of those who were to be remembered at the sacrifice) were now read and concluded with a prayer. Then the kiss of peace was given, and this too was followed by a prayer. The preface and the Sanctus were succeeded by a prayer which served to connect the Sanctus with the account of the institution of the Eucharist.
The text of the Gallican Canon has not come down to us, but there is reason for believing that it was quite short. The Consecration was followed by a prayer called the post-secreta or the post-mysterium. The Breaking of the Host was quite complicated, and the particles, usually nine in number, were arranged in the form of a cross. While this was being done, a clergy sang an antiphon.
The introduction to the Pater noster was variable. The priest and congregation recited the Lord's Prayer. Right after the commixtio a blessing was given, and a short chant called the Trecanum was sung during the distribution of Communion. The Mass ended with a prayer of thanksgiving and a collect.
-- William Bonniwell, A History of the Dominican Liturgy with a Study of the Roman Rite Before the Thirteenth Century, p. 5-6
See also:
Gallican Liturgy in The Catholic Encyclopedia
Msgr. L. Duchesne, Christian Worship: Its Origin and Evolution, ch. 7, "The Gallican Mass"
The Gallican Rite, W.S. Porter
