Limestone Sills and Strap Iron Rails
The limestone sills were quarried to standard sizes of approximately 1 foot by 1½ feet square by 4 to 6 feet in length. Some were reported as long as 10 to 20 feet. Mason chiseled the inside face with a straight notch for the wheel flanges (of about 3 inches by 3 inches) and then another straight indentation for the iron rails (of about 2½ inches by 5/8 inches). Holes were then drilled (with a diameter of ½ inches by 4 inches deep) into the sills at about 18 inch intervals for the rails. These holes are plugged with black locust dowels.
The sills were laid in two rows parallel in a gravel bed, so that the iron rails were spaced exactly 4 feet, 8½ inches apart, with about 6 inches above the surface. Crushed limestone was then filled in between the sill to create a horse path.
The iron rails were imported from England, by ship to New Orleans and steamboat to Louisville (or Frankfort). These iron straps measured 2¼ inches by 5/8 inches by 20 feet long. Holes were drilled to correspond to the holes in the limestone sills. The rails were then attached to the limestone sills by an iron spike driven into the black locust dowels. The drill holes were countersunk to allow the heads of the iron spikes to lay flat on the surface of the iron rail. The rails were laid so that the ends are not across from each other side.
On embankments and bridges, the limestone sills were substituted with parallel 6 inch square wooden rails. These rails are held in place by crossbeams underneath in 2 to 4 foot intervals. Another set of parallel rails were then tacked under the crossbeams. The iron straps would then be spiked to the parallel rails. Red cedar, white oak and pine rails were first used, however, with red cedar lasting the longest.
These limestone sills were assumed to be indestructible but quickly crumbled under the weight of steam locomotives. In 1843, the company replaced the limestone sills with cedar crossbeams. In 1850, the railroad then replaced the cedar crossbeams with cross ties and “T” rails.