This section, running through the townlands of Ardkill More, Largan, and Drumbarry, belongs to the linear earthwork traditionally known as the Black Pig's Race, or the Worm Ditch, a name that appears on Ordnance Survey maps as far back as the 1912 edition. The earthwork commences at a stream at the base of a steep-sided hill and runs roughly northwest to southeast for around 1,150 metres before changing direction and continuing east to west for a further 750 metres, finally terminating at the eastern bank of a stream in Drumbarry townland. In total, this is a substantial piece of ancient engineering, and yet much of it has been quietly absorbed into the ordinary fabric of the countryside.

The Black Pig's Race is a discontinuous series of linear earthworks found across Ulster, generally interpreted as a series of territorial or defensive barriers dating to the Iron Age, though their precise purpose and date remain debated. This Cavan section preserves some of its original profile where an active quarry has inadvertently revealed it: the rock-cut ditch measured roughly 3.5 metres wide and 1.3 metres deep in the quarry's northern face, and approximately 4 metres wide and 1.5 metres deep in its southern face. South of the quarry, the accompanying bank, between 5 and 7 metres wide and around 2 metres high on its western side, continues for approximately 700 metres before veering eastward. In Largan townland, the earthwork survives as a much-reduced earthen rampart, no more than 0.9 metres high and up to 7 metres wide, with the remains of a fosse, a defensive ditch, along its northern foot. Modern field drains have disturbed much of this stretch. Particularly curious is the presence of a rath, a roughly circular enclosed farmstead of early medieval date, built directly against the southern face of the rampart in Largan, suggesting that centuries after the earthwork was constructed, later inhabitants were still treating it as a meaningful feature of the land.