熟鐵
The timber track was soon replaced by cast iron fish-bellied rails on stone block sleepers, and in 1808 the track was again relaid, about two-thirds of the extent with rolled wrought iron rails and the remainder with cast iron. The line was famous for its early introduction of the new material. "[Wrought iron in edge rails] was first used by itself, without a wooden rail below it, in a humble way at Tindale Fell near Brampton in 1808 and at Walbottle about the same time."