The Maid on the Shore I'm thinking of is in a major key, but with consistently sharp subdominants (4s). That's Lydian, isn't it?

Maybe others don't hear it that way...all depends on what key you think it's in when you hear it, which in the case of an acappella piece could vary with the hearer. But I definitely hear it as Lydian, starting on the 6 of the key it's in and ending on the 2.