No, Catsmom, look in the corners, near the waterfall (not in the waterfall itself). If my memory is correct, the one I had trouble finding was in a corner at the front of the cave (where you came in) on the left side. I got up by the stepping stone, and hugged the wall all the way to the front. I had to go into the corner smack into the wall to engage it. Is that the one you're missing? I remember it took what felt like forever to find it. Just try sticking to the wall as best you can, using the conch to call it.
"How could drops of water know themselves to be a river? Yet the river flows on."
- Antoine de Saint-Exupéry