I have been looking at my previous correspondence, and came across our notes to one another, and I thought I would follow up with you. How have your searches been? I have had no luck in finding out info on your Robert Moses St. Clair. I have seen through other descendant's info that Moses and Catharine possibly had a son, Elias (unverified), who may be Robert's father, but I can not confirm. During my research, I came across this message on GenForum (see below). Have you seen it? The information in it could be a potential lead in regards to our Moses, and his origins. I have been unable to make contact with the writer of the post, since it is from 2007. Here is the post, in case you have not seen it:
Posted by Edith Tisdale on Sept 25/2007:
Does anyone have any information on RobertSinclair(St Clair) b-1680? He may have been born in New Hampshire.,
his parents were James St Clair and Deborah. He owned sawmills . He married Elizabeth Denmark.
They had one child John b-1713--d-1770
John was a millwright in Wells Maine.In 1739 he married Mary Wakefield. One of their children was Adoniram b-abt-1741 He married Elizabeth Joy-they were early settlers in Lisbon Maine.Here he was a miller. There were 8 children-John,Thomas,Joseph,Nathaniel,Mary,Ebenezer,Adoniram and Moses of this marriage-- Moses b-1787 married Catherine Elizabeth Fowler. Moses and Catherine would be my gg grandparents.
Maybe someone has info on the siblings of Moses I would be happy to hear from you.
The fact that this info lists Moses' father as Adoniram seems to tie into the letter your family line has. I do not have access to any U.S. records on Ancestry.com, but there are some Public Family Trees, which have some sources for this family.
Hope this helps!