The Mauch Chunk Switchback Railway ran down the side of a mountain. The reason it gets lumped in with roller coasters is because it was gravity powered...but in most regards it has more in common with a railroad than with a roller coaster. It was not built for the purpose of providing amusement, but rather for transporting coal. It did become a sightseeing/excursion train, though, once it was no longer needed for hauling the coal.
--Dave Althoff, Jr.
*** This post was edited by RideMan on 1/17/00. ***