Section of a Wilson variant plate rail from the Kilmarnock & Troon Railway. This variant – which was specified for replacement rails was invented by John Wilson (the railway company’s surveyor) – incorporated two feathers on the underside of the rail.
Note the considerable wear on the plate caused by iron-shod wheels.
For description of the railway see Proceedings of the Institution of Civil Engineers, Civil Engineering, 1998, 126, May, 73-85.
For a general description and images of early cast iron plate railways see https://tringlocalhistory.org.uk/Railway/c03_track.htm.
For an article on the viaduct and its restoration see http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=1243.