An area of low-lying land adjacent to the River Clyde, Float Moss is located a half-mile (1 km) southeast of Carstairs Junction. Regularly flooded in the Spring, the area takes its name from a flat-bottomed boat (or float) which provided a means of crossing. The name does not appear on maps, although the First Edition of the Ordnance Survey 6" (1859-64) shows Float Cottage to the south.
Float Moss is traversed by the West Coast Mainline Railway which passes over a series of low bridges and embankments that were constructed at great expense c.1847, including Float Viaduct - rebuilt in 1999 at a cost of £5 million to permit high-speed running. The line to Edinburgh once diverged at Float Junction, but this closed to through traffic in 1860 with its last use apparently being for the Royal Train conveying Queen Victoria (1819 - 1901), although it continued as a goods siding for a number of years thereafter. The Edinburgh branch now takes a rather sharper turn a half-mile (1 km) closer to Carstairs Junction, but the route of the Queen's Branch, as the old line from Float Junction became known, remains clear on the ground today.