I don't see that it is at all obvious.  For one thing, Eliot knew the rocks; he did not name them.  They already carried the powerful image of danger and beacon.  For another, he knew perfectly well that the pronunciation was not the same a "salvage" in the sense of redeem or save, and he took the trouble to give the source and pronunciation.  For another, Eliot has many agendae besides sin and redemption, however significant that is in 4Q.  In "The Dry Salvages," for example, he is also drawing on Indian sources--as you of course know, not just Christian redemption, and he is also moving back across the Atlantic from New England.  It is not a one-for-one allegory.  I think if we want to read these texts together, we have to avoid any notion that we can find a single, constant meaning like a grid to lay over every poem.

 

And as I've noted before, a great irony in Eliot's life is that nothing ever seemed to give him peace, ever, except human love with Valerie.  For all the ideas of discipline and self sacrifice and the disgust at copulation, none of the poems really reaches a sense of joy except that awful one about their love--awful as poetry but touching.

Nancy