The boundary line between Georgia and Florida shall be the line described from the junction of the Flint and Chattahoochee Rivers to the point 37 links north of Ellicott's Mound, on the St. Marys River; thence down said river to the Atlantic Ocean; thence along the middle of the presently existing St. Marys entrance navigational channel to the point of intersection with a hypothetical line connecting the seawardmost points of the jetties now protecting such channel; thence along said line to a control point of latitude 30 deg. 42' 45.6" north, longitude 81 deg. 24' 15.9" west; thence due east to the seaward limit of Georgia as now or hereafter fixed by the Congress of the United States; such boundary to be extended on the same true 90 deg. bearing so far as a need for further delimitation may arise.