near Kirkby Stephen
Nine arches of 30 feet span, built to a slight curve.
Merrygill Viaduct spans the narrow valley of Hartley Beck. Built of local limestone, Merrygill Viaduct has nine arches each of 30 feet span, with a total length 366 feet, and a height above the beck of 78 feet.
The route was heavily used by trains taking coke to Cumbria's blast furnaces, and between 1889-92 a second line was added to carry westbound trains, which involved building a second viaduct to the south side of the first. The complete structure is 25 ft 7" wide.
The 'Stainmore Railway', as the route was known, was closed in 1962, but a short section serving Hartley Quarry continued in use until 1975, although it split from the main line just west of Merrygill Viaduct.
Merrygill Viaduct and Podgill Viaduct, and Smardale Gill Viaduct, collectively known as the Eden Viaducts, are now owned by the Northern Viaduct Trust. See Northern Viaduct Trust website. Merrygill and Podgill viaducts are close together on a popular walking route.
Further information and map here.
Sources of Information
-  Forgotten Relics website - Merrygill Viaduct