Just stumbled across this on the net, researching Welsh roots to the song 'The Seamen's Hymn' found on THE REVELS' 'Blow ye Winds' CD.
Got to say, despite the 17-18th c. British 'West-Gallery' feel to it, the tune sounds distinctly rooted in the Gaelic countries instead. Those deep changes like 'The Ranger's Command' are found rather in Irish and Scottish melodies, Welsh melodies sounding more contained and from a different perspective. Irish and Scottish have a severe pentatonic world that sounds unresolved and hints at eternity. Such big melodic Gaelic changes can be heard most in Scottish ceòl mór music (Scottish Baroque bagpipe music), but I think this melody sounds more softer and Irish of origin.
Obviously it has been around in the mixing pot, thrown back and forward between the Irish, English, Americans, and maybe Welsh vicars too.