This junction was the southern apex of a triangular junction. The other junctions were Cleghorn Junction, to the west, and Silvermuir Junction, to the east.
The east to south curve opened for the opening of the Douglas Branch (Caledonian Railway) in 1864, an extension of the Lanark branch.
The original signal box was on the east side of the junction.
The box was replaced in 1934, as were all three junction boxes, with a single single box called Lanark Junction at Silvermuir Junction.
The Silvermuir South Junction to Silvermuir Junction curve closed in 1968.
The remaining line was reduced to a single track in 1971.
The Lanark Junction box closed in 1973, replaced by the Motherwell Signalling Centre.
| Silvermuir Siding|
Carstairs Sand Pit Signal Box
Caledonian Mineral Oil Works
Smyllum East Junction
Cleghorn Terra-Cotta Works
Smyllum South Junction
Smyllum West Junction
Cleghorn Clay Pit
Lanark Race Course
|Location names in dark blue are on the same original line.|
|/ /1860||Douglas Branch (Caledonian Railway)|
Line authorised: Smyllum Junction (Lanark) to Douglas. Smyllum Curve (Douglas Junction East to Douglas Junction South) and Silvermuir Curve (Silvermuir Junction to Silvermuir South Junction) also authorised.