That locomotive sounds like a super inefficient way to use magic to move a train. Of course it's simple, but there has to be many ways to turn magic more directly into mechanical movement. In fact since I doubt magic stones need to burn to produce heat (unless the proofreader is correct and it's just bloody coal), the efficiency of using steam would be greatly enhanced by using internal "combustion", instead of external. But I guess that would also depend on how those magic stones can be controlled to release heat.