While preparing for a seminar presentation on early Celtic Use liturgy, I discovered an online facsimile of the late VIII/early IX century Stowe Missal, Royal Irish Academy, Dublin, MS D.II.3. (When you follow the link, the menu appearing to the left on the screen will lead you to the images of the individual folios or pages of the Missal.)
Compared to the prayerbook of Catherine of Cleves (shared here earlier this week by Kimberly Belcher), the Stowe Missal is rather unattractive manuscript, with only a few illuminations, modest in comparison with the more famous Celtic evangeliaries or gospel books.
What makes the Stowe Missal worthy of note today is that the texts for the Ordinary of the Mass show evidence of development in two strata. The first stratum represented an early but rather conservative form of the Roman Liturgy, with certain Celtic features in the preparatory material and introductory rites, between the epistle and gospel lessons, at the offertory, and during the variable parts of the Canon. The redaction of the second stratum edited and developed these features (particularly at the offertory and during the Canon) resulting in a hybrid that betrays and conserves more features of the primitive Celtic use than the first stratum itself presented. In other words, the Stowe Missal gives an example of movement away from the increasingly dominant Roman liturgical forms of the day, perhaps in an attempt to preserve or even revive the older, more localized liturgical practice.