Boggy Man wrote:If my memory serves me correctly, wasn't the "quicksand" just leaves on water?

Not that I remember...it looked gray, but a little watery...and it left a nice gray coating on the victims once they were rescued!
It reminds me...the guy that stumbled in there did submerge! The doc reached under the surface to try to reach him, but pulled another previous victim out, who was obviously dead. After a minute, he was able to pull the other guy out:
Guy: What took you so long? I thought I was a goner!
Doc: We got sidetracked by another body that we pulled out from there.
Guy: What? You pulled that dead body out before you got me out?
Doc: Well, its only fair...he was in there longer than you!
I think you might be thinking of an older movie with an amazon in it, where 2 guys are fighting, and wander into the "quickleaves" while fighting. The amazon woman tries to rescue them, and starts sinking as well, but fails to rescue the guys due to their greed. Although it was leaves on water, the slow rate of descent did make it more convincing, and i did like seeing the woman sink before she was rescued.