The Canticle, if you listen carefully, starting the second verse, there is another melody and lyrics goes like
On the side of a hill in the deep forest green
Tracing a sparrow on snow-crested ground
Blankets and bedclothes the child of the mountain
Sleeps unaware of the clarion call
...
This is the Canticle, which the rhythm and melody counterpoint to the Scarborough Fair melody. For the detail mechanism, we need to go deep into counterpoint.