Are you sure that's the explanation? It could be (and I think it's more likely) that the rest of the stone was lightened, and the part in the shadow, wasn't.

Are you sure that's the explanation? It could be (and I think it's more likely) that the rest of the stone was lightened, and the part in the shadow, wasn't. No "residue of a person", just literally "shadow". See also: https://en.wikipedia.org/wiki/Human_Shadow_Etched_in_Stone https://en.wikipedia.org/wiki/Human_Shadow_Etched_in_Stone