I think you will find Grant-Stuart are two surnames which the person you are searching for has hypenated. Names were and still are hypenated for many reasons... to join two families together through marriage so as not to loose the identity of both parties, secondly to give the child the father and mothers names if they were not married etc,. Names such as Barclay-James or Llewellyn-Jones etc were hypenated for the above reasons, there are many more.

However, it is best to research BOTH singular names as they are from Gallelic decent, you might find that your ancestor may have hypenated it or his father.

Regards
Portland