Pollnacrom is part of the main Reyfad system and exploration has established the connection along the downstream section of the ‘Heaven and Hell' passage. It is entered by a small, unpromising hole in a field watered by a stream. The top few metres are through the cherty part of the Dartry Limestone but quickly reach the Knockmore Limestone below. As in Mad Pot (see site record ‘Reyfad-Carrickbeg; Mad Pot') and elsewhere, this limestone is characterised by long vertical pitches and here two shafts (the first 50m deep, the second 15m) give access to the main stream passage. This joint-controlled passage has a north-westerly trend for over 100m and then, at a junction, the main downstream passage turns south. It has been explored for 600m to an impassable sump. Attempts to force this route in 1981 resulted in the death of a diver.
Pollnacrom is described as part of the Reyfad system in the general account (see site record ‘Belmore, Ballintempo & Tullybrack Uplands; Reyfad-Carrickbeg'), where its significance in the wider karst development can be appreciated.
