The area known as "Carbon" or, I believe, Turton names Corbonais later became known as "Montagne" or Mortagne. Mortagne-au-Perche is within spitting distance of both Alencon and Belleme, both of which became seats of power for this family. There was a separate family (also having a Fulk) who were counts of Carbon and Mortagne. I don't believe that they were related.