I have long found this poem enchanting but also just a little annoying. I like to understand a poem as thoroughly as I can, and get frustrated when that understanding seems to require some private key that I don’t have. And this one, after its beautiful opening stanzas, appears to tail off into a slightly wilful irresolution. ‘Where have I seen before, against the wind, These bright virgins…?’. I don’t know, mate, where have you seen them before? And what’s with the scream?
I have seen it suggested that the allusion is to the story of Susannah and the Elders in the apocryphal addition to the Book of Daniel, but if that’s really what Ransom had in mind, I can only say that the parallel between two voyeuristic old men hiding in the bushes to watch a woman bathing and the awakening of a young boy to his first romantic perception of womanhood does not seem a particularly happy one. But I’ll forgive all for the willows, clouds, deep meadowgrass and the steep turn of Sweetwater.
Later: one suggestion I have had is that the boy is startled out of his daydreaming by one of the girls, who has ‘been adventuring with delicate paces’, falling into the steep-banked stream, hence the sudden cry.
Vision By Sweetwater
Go and ask Robin to bring the girls over
To Sweetwater, said my Aunt; and that was why
It was like a dream of ladies, sweeping by
The willows, clouds, deep meadowgrass and river.
Robin’s sisters and my Aunt’s lily daughter
Laughed and talked and tinkled light as wrens
If there were a little colony all hens
To go walking by the steep turn of Sweetwater.
Let them alone, dear Aunt, just for one minute
While I go fishing in the dark of my mind:
Where have I seen before, against the wind,
These bright virgins, robed and bare of bonnet,
Flowing with music of their strange quick tongue
And adventuring with delicate paces by the stream,
Myself a child, old suddenly at the scream
From one of the white throats which it hid among?
John Crowe Ransom
David Sutton 
I think the scream is about death. The flowing river of life, him mentally time travelling through his life’s adventures, rudely woken from his dream… the source unknown because it could have been any of them, death comes to us all.
Although I did wonder whether ‘the dark of my mind’ was dark enough for him to have wrung the neck of one of the ‘wrens’ / ‘hens’…
I’m writing a paper on this poem. It’s due in 2.5 hours. I’m pretty sure the scream was from my throat. 😉 I found your page in a web-search. Like all wanderers, I was looking for meaning, but at least I found camaraderie. 😀 Seriously: what is with this poem?!?
Just discovering John Crowe Ransom a short time ago.. I could not have helped you in 2015. But I doubt the dark symbolisms suggested in some of the critiques I’ve read of this poem are worthwhile reads. Instead, I’d rather believe the poem is narrated by a young fellow charged with seeing several young girls along a creek with some rugged terrain. Being young and healthy, he becomes enamored with their beauty, as a boy of the time might. So not paying attention, one of the girls slips on a steep edge, falling into the stream. I believe the ending suggests tragedy: “old suddenly at the scream from one of the white throats which it hid among.” I’d looked at pictures of Sweetwater Creek and there are several places where a person could fall to catastrophe.
Thank you. It’s good to get a ground view of the poem, and I always prefer a practical explanation myself where available.
“Where have I seen before …” – The girls walking beside the river make the boy try to recall a dream? “it” in the last line is the scream? In the dream one of the virgins screams but he can’t immediately tell which one? There’s no note of danger until she screams?