Well done Zak....give the man a coconut. It is the Trevithick Coalbrookdale locomotive from 1803.
To date, the only known information about it comes from a drawing preserved at the Science Museum, London, together with a letter written by Trevithick to his friend, Davies Giddy. The design incorporated a single horizontal cylinder enclosed in a return-flue boiler. A flywheel drove the wheels on one side through spur gears, and the axles were mounted directly on the boiler, with no frame. On the drawing, the piston-rod, guide-bars and cross-head are located directly above the firebox door, thus making the engine extremely dangerous to fire while moving. Furthermore, the drawing indicates that the locomotive ran on a plateway with a track gauge of 3 ft (914 mm).
This is the drawing used as the basis of all images and replicas of the later "Pen-y-darren" locomotive, as no plans for that locomotive have survived.