You're probably describing a "rail train" -- a long series of flat cars with special racks for holding continuous welded rail in 1/2 mile long sections. A flat on the end has a mechanism for loading and unloading the rail.
Here are some pictures of one parked on the BNSF.
http://www.mnnr.org/railroads/welded-rail/
By typing the search phrase welded rail train into Google you can even find some videos of rail trains at work or moving down the track.
http://www.youtube.com/watch?v=LHo-BqKLv8M
My dad sent me a photo of a special flat car he saw near his home, at a port town, Morehead City, North Carolina. We were trying to figure out what they were. Since they were parked near a large container crane, we assumed they were container flat cars. He has since found out that they are actually specialized flat cars that carry loads of railroad rails, that are shipped in. I was just wondering if any one else has seen this type of car, modeled it, or has any additional info?