A gradual compiled between the late eleventh and twelfth centuries, initially for the cathedral priory of Christ Church, Canterbury. It was taken to the cathedral priory of Durham by the early twelfth century (possibly as part of Bishop William of St Calais' donation of books). Further sections were added in the early thirteenth century by 2 scribes and are stave-ruled.

The added polyphony appears on fol. 125r in a late fifteenth-century hand. The two-voice polyphonic exercise texted ‘Amen’ has been added to the two lowest staves (pre-ruled c.1200 with three red lines each). Using ‘strene’ notation, it appears to be an exercise for the instruction of discant: for realising concords above a largely static tenor (thirds, fifths, sixths, and the octave), while creating sound melodic movement in the upper voice (e.g. the rising minor sixth interval from a to f).

93 folios

Mid-19th century full brown calf over thick wooden boards with 2 clasps (by Charles Tuckett, binder to the British Museum, who rebound most of the Cosin Manuscripts in the 19th century).

Late 11th-early 12th century, with early 13th century additions. Polyphony added late 15th century

3 red lines per stave, c.1200