Repeated investigations have gradually brought me to the conviction that the Finn or Seal stories contain a combination of the mermaid myth with a strong historical element—that the Finns are nothing else than a fabulous transmogrification of those Norse "sea-dogs," who from eld have penetrated into the islands round Scotland, into Scotland itself, as well as into Ireland. "Old sea-dog" is even now a favourite expression for a weather-beaten, storm-tossed skipper—a perfect seal among the wild waves.
The assertion of a "higher" origin of still living persons from Finns
... would thus explain itself as a wildly legendary remembrance of
the descent from the blood of Germanic conquerors. The "skin" wherewith
the Finns change themselves magically into sea-beings I hold to be
their armour, or coat of mail. Perhaps that coat itself was often made
of seal-skin, and then covered with metal rings, or scales, as we see it in
Norman pictures; for instance, on the Bayeux tapestry. The designation
of Norwegian and Danish conquerors, in Old Irish history, as "scaly
monsters," certainly fits in with this hypothesis.