I do believe the faint line is that which is used to at a crime scene when someone has died to outline the exact position the body lay, so if such a thing exists, maybe Amy should look around for the police, as there has to be some in the abyss if this outline is there.
Am I the only one who thinks Amy should worry a little more about what is happening around her? See what do the walls of the hole look like. I didn't want any kind of chemical composition or anything, just know what are they like. Smooth? Rough? Dinosaur bones sticking out? The entrance to Lost City in eye's height? Cut off underground water flows flooding the street Amy walks? That kind of obvious stuff.
I think it's more important what is not happening around her. Surely there should be people screaming about the fact they've all fallen into the abyss!? Though Amy seems to be quite content with this occurrence.
I agree with the notion of examining the note more carefully. She doesn't need to touch the thorns go get the note from between the petals.