In White Mountain, there are two types of bedrock. Slates and schists, types of metamorphic rocks, are found on the eastern slopes, and granites, types of igneous rocks, are found on the western slopes. These geological divides closely align with the county boundary, running along the mountain’s crest with Wexford to the east and Carlow to the west. While there are visible bedrock outcrops on the higher parts of the mountain, the slopes and lower regions are covered by glacial deposits that have been creeping slowly downslope under the influence of gravity.
During the last ice age, ice acted on the mountains polishing the landscape. Even so, White Mountain was less affected by ice than the neighbouring Wicklow Mountains. This caused glacial landforms in this region to be visibly less well developed when compared to Wicklow and other Irish uplands. However, the shorter exposure to destructive glacial forces in the Blackstairs helped the survival of fascinating features like tors, known locally as Brans, in the higher areas. These landforms would have otherwise been worn away by the force of ice, leaving a more polished land surface. Other landscape features found near White Mountain include blockfields, bedrock moulded by ice, and meltwater channels through which water flowed as temperatures rose at the end of the last ice age.
As you walk along White Mountain, you may come across pieces of white quartz, granites, as well as different minerals, notably some shiny, silvery sheets called muscovite or mica, a common rock-forming mineral.