re: Could the name Foster be an adaptation of the name Forster?
Yes, Mary, although I have not yet researched if any of this Foster / Forster family traded in America.It may be likely as their cousins, the Molesworths were in London, in the Trade and Plantations Department.
The old file I have at home compiled about 1860s by a Mr. Hartley of Beech Park, Clonsilla, co. Dublin (may have been a sheriff of Dublin) writes :
James Foster daughter of The Hon. Col. Richard Foster of Dublin Esqr. lineally descended from Sir Richard Foster Knt Bannerett who was originally descended from EGERIT Knt. of the Black Forest Germany, who was great grandson of Robert, Earl of Hapsburgh, in Germany.The said Colonel Richard Foster, married Anne, daughter of ...... Ellock, by whom he had issue, three sons and four daughters. 1st. The Right Hon. John Foster, Lord Chief Justice of The Common Pleas. 2nd. Nicholas, Lord Bishop of Raphoe, 3rd. Col. William Foster. 1st. eld. dau, Elizabeth married John Cooke of Cookesborough, in the County Westmeath Esqr. 2nd. Jane (as above) 3rd. Anne unmarried, 4th. Letitia who married Thomas Gay of Redmondstown in Co Westmeath Esq.
It then goes on listing the daughters of Robert Adair by Jane Foster, descendants of whom were The Hartley's of Beech Park.
This Mr. Hartley also enquired at a Gentlemen's Club in Dublin about Robin Adair, husband of Lady Caroline Keppel, and another gentleman of the Club wrote on the enquiry that Robin had been educated at Leyden.I think that if he were "our" Robin, Mr. Hartley would certainly have known.
Robert Adair who m. Jane Forster / Foster was son of Charles and Elinor Adair (nee Cooke of Cookesborough, co Westmeath). Appears that Robert Adair's sister-in-law also m. a Cooke of Cookesborough.