So melting the iron, once I got a strong enough forge built out of rock, was not really a problem. Takes a lot of wood, throws a lot of probably-caustic fumes, smells horrible, glad it’s not in my cavern, but workable.
The sandy clay not so much. The sand and clay both kind of.. well, not melted, but the clay made sort of a ceramic and the sand didn’t melt, it just sort of… stuck… to stuff, so my iron rails are more like iron-filled-with-air-bubbles-and-impurities.
I think I’m going to need to build a frame and fill it with either clay or sand to make these rails.
I also think clay will be easier to work with.