Unfortunately, I cannot be much help to you.Your line was probably part of an earlier migration to America than mine was.At some point back in Ireland or Scotland, the lines probably come together, but it's hard to say how far back.
The reason I say it was an earlier migration is that the first "Scotch-Irish" settlers settled in Western Pennsylvania at the invitation of the colonial government.In fact, many of the Scotch-Irish settlers landed in Pennsylavania and then moved south to Virgina and North Carolina.Pennsylvania originally was a good place for settlement due to peaceful relations with the Indians - fostered by the Quaker colonial government.However, as the settlers arrived, Indian attacks began and the settlers were frustrated by the lack of action from the colonial government.
Settlers were lured to the South by offers of cheap - and often free - land.Thus, the later migrations settled heavily in the Shennandoah Valley and western North Carolina.
Your ancestors were in all probability Scottish Presbyterians.Very few native Irish had immigrated to America at this time.The "Scotch-Irish" were often considered Irish (they even considered themselves Irish to a degree) because they came from Northern Ireland.However, they had settled in Northern Ireland from Scotland.See my earlier postings on the history of the Scotch-Irish, the Ulster Plantation and the Adams Sept of the Scottish Clan Gordon.In fact, many people today who consider themselves of Irish descent are in fact of Scottish descent.The Scotch-Irish made up about 10% of the colonial population at the time of the Revolution.
I hope this is of some help.I can also suggest you read "The Scotch-Irish of Colonial Pennsylvania" by Wayland Fuller Dunaway.There are also a number of other books on the subject of the "Scotch-Irish" available at your library.