Cosher (Crawshay) Bailey really did have an engine, and it probably looked something like this. That sort of design was obsolete even when it was new in 1832, but they kept making whole fleets of these in South Wales for years afterwards. Stubbornness, parochialism, building cost... it didn't matter that they were massively inefficient, the coal was effectively free. You might notice that in the drawing the wheels don't seem to sit on the rails. This isn't a mistake, on most of the South Wales lines the rails were flanged and the wheels plain, an engineering error- rails are stronger when you have the load- bearing element vertical- that lasted from the 1780s to the 1830s for new builds and up to the 1920s in service.