A Mass of thanksgiving was celebrated July 1 at the diocesan officess at 310 Prospect Park West to mark the retirement from diocesan duties of Sister Angela Gannon, C.S.J., secretary for education and formation. Bishop Nicholas DiMarzio, shown with Sister Angela at a luncheon following the liturgy, was the main celebrant. He was joined on the altar by other priests who work in diocesan administration. Sister Angela will continue to serve her community, the Sisters of St. Joseph, Brentwood, L.I.