the bold anfractuous rocks
Faced by the snarled and yelping seas.

an, around + frangere, BREAK


I think this may be a witty word-play that goes back to the etymology - the sea breaks around the rocks.

Eliot could have had this in mind as well as the image of the rocks being twisted back upon themselves, and as well as the concept of there being no possible path through the rocks.

Excellent poetry.