Toward a reconstruction of a common ground of the Celtic Church calendar and the so-called "Old Norse" calendar
From the Celtic side, we have while indirect, but very strong evidences of the days of the months as assigned fixed days of the week, and also a direct evidence of the seven-year calendarical cycle.
From the "Norse" side, we have a surviving 364-day calendar and a direct testimony of some "Judaizing" features of the Celtic diaspora monks.
Moreover, we have a synchronism between the persecutions of the Celtic customs in Ireland and beginning of the Celtic monastic colonisation of the northern islands.
There are two conclusions to be drawn:
1. The calendar of the Celtic Church was the 354-day calendar of some kind, and
2. The "Old Norse" calendar is a part of the legacy of the Celtic diaspora monks, the papar.