"well" or "whelm"

Hello,

Please tell me if it is "well" or "whelm" in this verse in the song "The Sound Of Silence" (by Paul Simon) (1964):

"Fools," said I, "You do not know
Silence like a cancer grows
Hear my words that I might teach you
Take my arms that I might reach you,"
But my words, like silent raindrops fell
And echoed in the whelms/ in the wells (???) of Silence

THANK YOU!