Sea-change or seachange is a poetic or informal term meaning a gradual transformation in which the form is retained but the substance is replaced, in this case with a marvellous petrification. It was originally a song of comfort to the bereaved Ferdinand over his father’s death by drowning. The expression is Shakespeare’s, taken from the song in The Tempest, when Ariel sings,
“Full fathom five thy father lies,
Of his bones are coral made,
Those are pearls that were his eyes,
Nothing of him that doth fade,
But doth suffer a sea-change,
into something rich and strange,
Sea-nymphs hourly ring his knell,
Ding-dong.
Hark! now I hear them, ding-dong, bell.” – Wikipedia