Writing in The Musical Quartely, Jan - Oct 1936, George Pullen Jackson says, "The tune of the religious song above, Saw ye my Saviour, is the old Scotch air Saw ye my father or Grey Cock, according to Gilchrist (Publications of the (English) Folk Song Society, vol Vlll) and is found in both Scotch and Enlish versions. In 1834 the same appeared in Foster's own state in the German Kirchen-Harmonie, Chambersburg, Penna., p. 42, under the title Lobet den Shopfer." Jackson was comparing Old Black Joe with the melody of Saw ye my Savior.
He goes on to write ".... other echoes of the same old Scotch folk-tune appear in .....".
I noticed many examples of Scottish melodies used by Foster, too numerous and thread drifting to print here.