I’m looking for a children’s or YA novel about St. Cuthbert, the Holy Island of Lindisfarne, some children, and possibly a selkie (mythological creature). The story, as I remember, was somewhat mystical and had to do with St. Cuthbert. I would have read it in the late1960s— it’s not The Wind Eye by Robert Westell (1977), which was published too late to have been the book I read. I remember the cover being illustrated in shades of gray and white. It may have shown some birds flying around the island, which has a distinctively shaped profile.