Example of a stone block used on the Kilmarnock & Troon Railway to support the rails. The stone has a hole 1.5 in diameter and 5 in deep on the top side into which an oak plug had been inserted. A rail chair was positioned over this plug and two plate rail lengths were secured at their ends by a malleable iron nail (see 1997/011) which was hammered to be flush with the rail, passing through a hole in the rail chair to be secured in the oak plug. The figure to the right of the image shows the general layout of the stone, chair and rails.
For an article on the viaduct and its restoration see http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=1243.