"A Survey of the Northern Neck of Virginia: Being the Lands Belonging to the Rt. Honourable Thomas Lord Fairfax Baron Cameron, Bounded by & Within the Bay of Chesapoyocke and Between the Rivers Rappahannock and Potowmack : With the Courses of the Rivers Rappahannock and Potowmack, in Virginia, as Surveyed According to Order in the Years 1736 & 1737."
You may read the details of the final survey conducted in 1746 here (link).