Does anyone know what this tune is?

Music A tune has been rattling around my brain for hours but I can't put my finger on what it is. Here's my attempt at singing it. Does anyone have any ideas?



Press play now ...

UPDATE:

It's from Ennio Morricone's soundtrack to Terrance Malick's film Days of Heaven:



Not bad. I worked it out on my way to work today. I remembered this shot of Richard Gear attop a train:



And though they don't appear together in the actual film, I think, they do during the documentary about cinematogaphy Visions of Light, which draws much of its music from Morricone's themes for Terrance Malick's film.

The melody for this is very much like opening few bars Medieval composer Jacque Arcadelt's Ave Maria [spotify] [youtube] which is what I was listening to last night and set me off.

The stuff I have rattling about in my head...