There was a great programme on BBC a few Years back about this very subject Blissy. It was brilliant and showed the Music trail from Scotland to the Folks that settled here in the US and developed it into their own Sound.
It showed how the Fiddle styles developed and the tuning in Harmonies.
Ill do a bit of investigating and see if I can find more info about it and let you know.
Blessings
Jude