The coal car is on tracks that lead directly into one section of the rock wall. A small button labeled Auuuugh! is bolted onto the side of the car.
As if in a dream, you climb into the car. You snap out of it. Clearly, you need to make a decision.
Do you hit the button and trust to fate or do nothing?
Whoops! You come to a dead end in the cavern. The vein clearly continues into the rock, but the passageway has ended for now. Then you realize that there is no distinct way back.