Sharon, after scanning your site late last night I sent you an email about some of my findings.Now this morning after checking again on Abraham b. 1757-d. 1843 and comparing what you have to the letter at the end of John Beverly's Book 'Riggs in Maryland' discover that that the note gives this Abraham a different set of parents and grandparents than the information you have gathered.
Your information gives him Parents Abraham, grandfather Joseph, g. grandfather Abraham.
The letter in John Beverly Riggs' book seems to gives him parents John b about 1622 in England, grandfather John b. 1667 in Va, G. grandfather Robert in Westmorland Co in 1728-d. 1770 in Va, G. G. grandfather Abraham b. westmoreland 1757 died Lousiana 1843.
I am puting the information here in hopes someone will have more to add to this site and yours and unscramble this.
Your site is so interesting and I will be reading it more closely soon.