Inheritability of Chestnuts on Icelandic Horse

I am posting this more as interesting trivia than scientific fact. In 1905, Annandale and Marshall published their book "Iceland and the Faroes:Studies in Iceland Life" Available via Hathitrust Library. at
http://babel.hathitrust.org/cgi/pt?id=mdp.39015067063340;page=root;view=image;si\
ze=100;seq=7;num=i

Predating the Watson and Crick discovery of DNA helix by about 50 years, they attempt to determine the origin of various animal breeds in Iceland and the Faroe Islands. They make an interesting comment about the inheritance of chestnut (the callous). Evidently some Shetland ponies are noted for not always having chestnuts on their back legs. So the authors were able to speculate that the Vikings brought some breeding stock from the Northern British Islands based on what they assume is an inherited characteristic.

"...the majority even of the heavily built Icelandic ponies are 'Celtic' in some of their characters, the hock callosities being often either wholly absent or very much reduced, and the tail possessing a more or less obvious caudal fringe."

On pages 180-181, the authors also relay the story of how sheep are herded in Suderoe, part of the Faroes islands. These horses are closely related to the Icelandic, a little lighter and swifter, but are better trained. The horse and rider and dogs chase after the sheep at mad speed. If the rider reaches down to grab the sheep, the horse traps the sheep between his legs to hold it for the rider.

I was always fascinated by that story. I can see Blessi being trained to catch sheep this
way.