UNDERGROUND KARST
The Reyfad-Pollnacrom-Polltullybrack cave system is developed mainly in the Knockmore Limestone Member. The regional dip is typically 10-20 degrees, varying in direction between west and south. The cave formation is predominantly aligned on two sets of fractures, trending approximately 340° and 010°. There are only a few E-W controlling joints. The horizontal part of the cave has formed between 230m and 130m amsl.
The Polltullybrack passage is developed in thinly bedded Cherty Facies of the Dartry Limestone, showing the typical features of this lithological unit. After 300m of low wet horizontal passage the stream breaks through into the Main Aven, formed in the massively bedded Knockmore Limestone Member where dramatic vertical development has occurred. The Main Aven is a 53m active underground shaft with a classic elliptical cross section and fluted walls. A vadose canyon leads from the aven and after 100m an inlet enters from Rory's Aven. This water, which is assumed to originate from Bush Sink, has developed a series of short vertical shafts joined by sections of canyon passage.
The Main Stream Passage canyon develops in size to the north attaining heights of 10-15m before suddenly changing direction to the southwest at the Grottoes. The canyon has a number of areas of breakdown and speleothem deposits, including an impressive stalagmite (the Virgin Mary). In the Grottoes area there are some of the finest speleothem deposits in the system with good examples of straw stalactites, helictites, curtains, columns and the stalagmite bosses known as The Fried Eggs. Much of the calcite has mineral staining giving great colour variation but much of the calcite floor deposits are on sands and muds which are now being eroded by water, causing subsidence of some speleothems. The stream follows 200m of canyon with major breakdown to the next inlet which enters via the Reyfad entrance shaft. The passage morphology changes dramatically in this area.
