Complex sentence: Paris revised Roger's work, and that of Abbot John de Cella, adding new material to cover his own tenure, and this "Chronica Majora" is an important historical source document, especially for the period between 1235 and 1259.
Split into simpler sentences: Paris revised Roger's work, and that of Abbot John de Cella, adding new material to cover his own tenure. This "Chronica Majora" is an important historical source document, especially for the period between 1235 and 1259.