The ramp being used to return to the area around the emerald block has always been my theory as well. Take a look at the water slides at the top of the ramp, the direction of the flow changes one "bump" after the start of the slides. It's possible you would've been dropped out at that point, if you held right you'd go on to the rest of the level, if not you'd be carried back down the ramp and have to get up there again. The way the zone is laid out I'm imagining it would've played like Labyrinth Zone, looping back on itself until you went the correct way. Of course that whole area is the least finished part of the zone and the section most likely to have been cut had the layout been reworked.