> Sorry to do this again, but I've been at this for hours.
>
> I'm in the sandstone caverns with a working map. I know of three exits out of the caverns besides the 3d barrier. I think I'm supposed to get the cart rolling again, but have no clue as to how I catch up with it, or where, or why. It seems from reading relevant posts that I'm on the right track. I've broken the pillar, so that's not a problem. Any tips would be great.
>

If you exit on the black level, you'll see that the rails pass by there. Just as further north in the mines, you can't ride in mine cart through the section of tunnel north of that, because it's too narrow, which necessitates doing the jump and catch the cart trick again. And just like the first time, you'll see that there's a chasm to the south that the railway passes over that you *need* to ride across, because it won't let you cross on foot.

So, just like before, you just need to jump from the right spot and make it down to that exit in as few moves as possible.