Guernsey or Garnsey??????

My ggg Grandmother was Martha Guernsey, born in 1814 in South Mountain Dundas Co. Ont. It is listed that her father was Samual Garnsey.I don't know why the spelling difference. Samual Garnsey married Sarah Bull.Is anyone out there a Guernsey or Garnsey in Dundas Co... Any kind of info would be neat.Thanks....Nadine