This study was initiated to solve a stratigraphic problem for the Geological Survey of Northern Ireland prior to the revision in 1997 of the 1:250000 map of the solid geology of Northern Ireland. An exploratory drilling programme carried out by the Survey in 1983/1984 revealed the existence of previously unknown Tertiary sediments north west of the Tow Valley Fault. The boreholes revealed a sequence of clays and lignites that were attributed to the Lough Neagh Group. These lay above an interbedded sequence of litho marge, pyroclastics and lacustrine deposits termed the Dunaghy Formation. The Geological Survey required an age to be assigned to this formation and it was proposed that the use of the preserved pollen and spore assemblages offered the best means for dating the sequence. In order to achieve this four boreholes were analysed. Boreholes 13/611, 13/603, 36/4680 and 27/415 contain the Lough Neagh Group. In addition 13/611 and 13/603 contain the Dunaghy Formation. From the pollen and spore assemblages recovered an Oligocene age IS confirmed for the Lough Neagh Group and proposed for the Dunaghy Formation. This information led to the attribution of an Oligocene age to the Dunaghy Formation in the 1997 revised 1:250000 Geological Map of Northern Ireland. The palaeovegetation deduced from the recovered pollen and spore assemblages is in accordance with an Oligocene cooling. The climax angiosperm vegetation, predominantly consisting of temperate forms with some megatherm taxa, grew in a raised bog forest ecosystem within a fluvial-lacustrine environment. All pollen and spore taxa recovered are described including new forms identified. A correlation of the four sections is proposed.